[Federal Register Volume 89, Number 102 (Friday, May 24, 2024)]
[Rules and Regulations]
[Pages 45944-45977]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-11192]
[[Page 45943]]
Vol. 89
Friday,
No. 102
May 24, 2024
Part II
Department of Transportation
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Federal Aviation Administration
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14 CFR Part 21
Airworthiness Criteria: Special Class Airworthiness Criteria for the
Archer Aviation, Inc. Model M001 Powered-Lift; Final Rule
Federal Register / Vol. 89 , No. 102 / Friday, May 24, 2024 / Rules
and Regulations
[[Page 45944]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 21
[Docket No. FAA-2022-1548]
Airworthiness Criteria: Special Class Airworthiness Criteria for
the Archer Aviation, Inc. Model M001 Powered-Lift
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Issuance of final airworthiness criteria.
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SUMMARY: The FAA announces the special class airworthiness criteria for
the Archer Aviation, Inc. (Archer) Model M001 powered-lift. This
document sets forth the airworthiness criteria the FAA finds to be
appropriate and applicable for the powered-lift design.
DATES: These airworthiness criteria are effective June 24, 2024.
FOR FURTHER INFORMATION CONTACT: James Clary, Emerging Technology
Coordination Section, AIR-611, Policy and Standards Division, Aircraft
Certification Service, Federal Aviation Administration, 10101 Hillwood
Parkway, Fort Worth, TX 76177; telephone 817-222-5138; email
[email protected].
SUPPLEMENTARY INFORMATION:
Background
On March 30, 2022, Archer applied for a type certificate for the
Model M001 powered-lift. The Archer Model M001 powered-lift has a
maximum gross takeoff weight of 6,500 lbs. and is capable of carrying a
pilot and four passengers. The aircraft has a high-wing and V-tail \1\
configuration with fixed tricycle landing gear. The aircraft uses 12
electric engines powered by onboard batteries for propulsion instead of
conventional air and fuel combustion. Six engines with five-bladed
variable-pitch propellers are mounted on the forward edge of the main
wing, three to each side, which are capable of tilting to provide both
vertical and forward thrust. The other six electric engines drive two-
bladed fixed-pitch propellers and are mounted on the aft edge of the
main wing, three to each side; they are fixed in place to provide only
vertical thrust. The aft-mounted engines operate only during thrust-
borne or semi-thrust- borne flight; in wing-borne forward flight, these
engines are switched off and the propellers are faired in line with the
aircraft fuselage. The aircraft structure and propellers are
constructed of composite materials. The Archer Model M001 powered-lift
is intended to be used for Title 14, Code of Federal Regulations (14
CFR) parts 91 and 135 operations, with a single pilot onboard, under
visual flight rules (VFR).
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\1\ A V-Tail aircraft design incorporates two slanted tail
surfaces instead of the horizontal and vertical fins of a
conventional aircraft empennage. The two fixed tail surfaces of a V-
Tail act as both horizontal and vertical stabilizers and each has a
moveable flight-control surface referred to as a ruddervator.
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The FAA issued a notice of proposed airworthiness criteria for the
Model M001 powered-lift, which published in the Federal Register on
December 20, 2022 (87 FR 77749).
Discussion
Because the FAA has not yet established powered-lift airworthiness
standards in 14 CFR, the FAA type certificates powered-lift as special
class aircraft. Under the procedures in Sec. 21.17(b), the
airworthiness requirements for special class aircraft, including the
engines and propellers installed thereon, are the portions of the
requirements in 14 CFR parts 23, 25, 27, 29, 31, 33, and 35 found by
the FAA to be appropriate and applicable to the specific type design
and any other airworthiness criteria found by the FAA to provide an
equivalent level of safety to the existing standards. These final
airworthiness criteria announce the applicable regulations and other
airworthiness criteria developed, under Sec. 21.17(b), for type
certification of the Model M001 powered-lift.
The Model M001 powered-lift has characteristics of both a
rotorcraft and an airplane. It is designed to function as a rotorcraft
for takeoff and landing and as an airplane cruising at speeds higher
than a rotorcraft during the enroute portion of flight operations. The
electric engines on the Model M001 powered-lift will use electrical
power instead of air and fuel combustion to propel the aircraft through
six five-bladed composite variable-pitch propellers for all phases of
flight, and six two-bladed fixed-pitch propellers for vertical and
transitional flight modes only. Accordingly, the Archer Model M001
powered-lift proposed airworthiness criteria contained standards from
parts 23, 33, and 35 as well as other proposed airworthiness criteria
specific for a powered-lift and the electric engines and propellers
installed thereon.
For the existing regulations that were included without
modification, the proposed airworthiness criteria included all
amendments to the existing parts 23, 33, and 35 airworthiness standards
in effect as of the application date of March 30, 2022. These are part
23, amendment 23-64, part 33, amendment 33-34, and part 35, amendment
35-10.
The Archer Model M001 powered-lift proposed airworthiness criteria
also included new performance-based airworthiness criteria. The FAA
developed these criteria because no existing standard captured the
powered-lift's various flight modes and electric engines and some
unique characteristics of their propellers. The new requirements
specific to the Archer Model M001 in the proposed airworthiness
criteria used an ``AM1.xxxx'' section-numbering scheme.
Because many of the proposed airworthiness criteria are
performance-based, like the regulations found in part 23, the FAA has
proposed to adopt Sec. 23.2010 by reference, which would require that
the means of compliance used to comply with the airworthiness criteria
be accepted by the Administrator. Because no powered-lift consensus
standards are currently accepted by the Administrator, the means of
compliance will be accepted through the issue paper process.\2\
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\2\ See Order 8110.112A, Standardized Procedures for Usage of
Issue Papers and Development of Equivalent Levels of Safety
Memorandums.
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Summary of Changes From the Proposed Airworthiness Criteria
These final airworthiness criteria reflect the following changes,
in addition to others as explained in more detail under Discussion of
Comments: The FAA made changes to the aircraft performance section to
incorporate an optional, ``increased performance'' approval, which
requires greater aircraft performance capabilities beyond that of the
baseline ``essential performance'' approval. The expectations for
aircraft performance at both levels are clearly defined at the
requirement level. Requirements to address various scenarios involving
failures that can lead to loss of thrust were clarified and
consolidated into a consistent terminology across all airworthiness
criteria. Expectations were added for the aircraft to be capable of a
controlled emergency landing following any condition where the aircraft
can no longer provide the commanded power or thrust required for
continued safe flight and landing (CSFL). The proposed requirement to
incorporate a bird strike deterrent system was not adopted in these
final airworthiness criteria, nor were other requirements not
applicable to the Model M001, such as requirements for operations on
water, approval for aerobatic flight, and others, as discussed in
further detail under
[[Page 45945]]
Discussion of Comments. The FAA modified and developed revised
aeroelasticity criteria to more directly address concerns expressed by
commenters related to ``whirl flutter'' and aeromechanical stability.
The FAA revised requirements in response to numerous comments
requesting clarification or recommending changes to address safety gaps
in the proposed criteria, particularly in the areas of aircraft
handling and control, structural airframe loads and durability, flight
controls, protection of occupants, and protection of systems from high-
intensity radiated fields (HIRF) and lightning. The FAA updated
requirements for electric engines in response to requests for improved
clarity on applicability and relationship to the airframe requirements.
The FAA also updated definitions for ``controlled emergency landing,''
``CSFL,'' and ``sources of lift'' and added a definition for ``local
events.''
Lastly, the FAA clarified that, should Archer apply to amend the
type certificate to include another model powered-lift, these
airworthiness criteria would apply to that model also, provided the
criteria remain appropriate to the changed aircraft in accordance with
part 21, subpart D. This change was necessary so that each future
change to the aircraft will not necessarily require an application for
a new type certificate.
Discussion of Comments
The FAA received responses from 22 commenters. The majority of
commenters were government agencies, private companies, and
organizations as follows: Ag[ecirc]ncia Nacional de
Avia[ccedil][atilde]o Civil (ANAC); Airbus; Air Line Pilots Association
(ALPA); Alaka[revaps]i Technologies Corporation (Alaka[revaps]i);
Aerospace, Security and Defence Industries Association of Europe (ASD-
Europe); Association for Uncrewed Vehicle Systems International
(AUVSI); United Kingdom Civil Aviation Authority (UKCAA); European
Union Aviation Safety Agency (EASA); General Aviation Manufacturers
Association (GAMA); IPR; Japan Civil Aviation Bureau (JCAB); Leonardo
Helicopters (Leonardo); Lilium eAircraft GmbH (Lilium); Odys Aviation
(Odys); Overair Inc. (Overair); Rolls-Royce Deutschland Ltd & Co KG
(Rolls-Royce); SkyDrive, Inc. (SkyDrive); Transport Canada Civil
Aviation (TCCA); Vertical Aerospace; and Volocopter GmbH (Volocopter).
The FAA received comments from one individual commenter and from one
anonymous commenter as well.
Support
AUVSI and ASD-Europe expressed support for type certification of
the Model M001 as a special class of aircraft and establishing
airworthiness criteria under Sec. 21.17(b). ALPA expressed support for
the use of 14 CFR part 35 propeller airworthiness standards.
Definitions
The FAA proposed criteria that created new or modified definitions
for the Model M001 powered-lift. The FAA received and reviewed comments
from ASD-Europe, ALPA, Alaka[revaps]i, ANAC, EASA, GAMA, Leonardo,
Lilium, Odys, Overair, TCCA, UKCAA, and an individual commenter that
requested the FAA clarify, revise, or adopt as proposed certain
definitions. Specifically, these comments were focused on the topic
areas of ``CSFL,'' ``controlled emergency landing (CEL),'' and ``loss
of power/thrust,'' along with requests for clarification on other uses
of the term ``thrust.'' GAMA and Overair also proposed modifications to
the ``source of lift'' definition. Additionally, comments from Airbus,
ALPA, ASD-Europe, EASA, Odys, TCCA, UKCAA, and an individual commenter
requested the establishment of a higher safety target for powered-lift
like the Model M001. In response, the FAA created an ``increased
performance'' approval that may be granted based on the aircraft's
ability to meet higher performance standards for continued flight under
certain failure conditions. The FAA modified AM1.2000(a) to provide for
the higher safety target of ``increased performance'' as well as to
establish the proposed minimum safety target for CSFL as ``essential
performance.'' The Model M001 must meet either the essential or
increased performance requirements in this certification basis.
Additionally, the Model M001 may be approved for both essential and
increased performance with appropriate and different operating
limitations.
The FAA has modified the definition of ``CSFL'' to establish the
different expected outcomes based on the performance approval sought.
The definition of ``CSFL'' was modified slightly for the essential
performance approval to include pilot alertness; however, the ability
to continue to the planned destination or alternate is a requirement to
meet the increased performance approval. Increased performance is a
higher level of safety that guarantees fly-away capability after any
failure not shown to be extremely improbable. Essential performance
does not require the aircraft to have the capability to land at the
planned or an alternate landing site as is required for increased
performance.
Several commenters suggested the FAA adopt EASA's special condition
for vertical take-off and landing aircraft (SC-VTOL) requirements for
powered-lift. The FAA disagrees and has instead adopted ``essential''
and ``increased'' performance approvals. Although the FAA's
``essential'' and increased'' performance approvals are similar to
EASA's ``Category Basic'' and ``Category Enhanced'' approvals,
differences remain. The FAA is establishing these airworthiness
criteria for the Model M001 to provide a certification basis for
aircraft design approval, while the operational approval is
accomplished outside of the aircraft certification process.
Additionally, both the FAA's and EASA's performance levels include the
aircraft's ability to conduct a controlled emergency landing after a
condition when the aircraft can no longer provide the commanded power
or thrust required for CSFL as specified in AM1.2105(g). To complete
the integration of these defined levels of safety requirements, the FAA
modified AM1.2115 ``Takeoff performance,'' AM1.2120 ``Climb
requirements,'' and AM1.2130 ``Landing'' to incorporate the essential
and increased performance requirements.
The FAA received several comments that the proposed definition of a
``CEL'' was not sufficient to ensure that the relevant instances that
may be encountered in operation are addressed beyond a ``critical loss
of thrust'' as required under the proposed AM1.2105(g). The FAA agrees
with the concerns raised by these commenters. As such, the FAA revised
the proposed CEL definition and the requirements of AM1.2105(g) to
establish the minimum level of safety required when the aircraft can no
longer provide the commanded power or thrust required for CSFL.
One commenter requested the FAA remove the part of the CEL
definition that requires that the pilot be capable of choosing the
direction and area of touchdown and instead require a controlled
descent. As indicated by the term itself, ``controlled emergency
landing'' is a defined airworthiness attribute in which the design
maintains sufficient control to change direction to an area of
touchdown, while reasonably protecting occupants from serious injury.
However, the FAA has updated the definition of CEL by relocating the
pilot reference to focus the requirement on aircraft functionality.
Overall pilot controllability requirements are addressed in AM1.2135,
which requires that the aircraft be controllable and maneuverable
without requiring
[[Page 45946]]
exceptional piloting skill, alertness, or strength. The intent of the
definition of CEL is to provide equivalency to the part 23 airplane
gliding requirements and the part 27 rotorcraft autorotation
requirements. Both minimize the aircraft's speed (forward and
vertically) while still allowing directional control of the aircraft to
an emergency landing.
One commenter requested the FAA clarify the statement ``reasonably
protecting occupants'' in the definition of ``CEL'' and further
commented that non-participants should also be protected since these
aircraft plan to operate in highly-populated urban environments. The
FAA agrees with the need to provide additional clarity and has modified
the definition of CEL to clarify that the expected safety outcome is
protection from serious injury, which inherently provides a level of
protection for non-participants on the ground. This approach is similar
to the level of safety in Sec. Sec. 23.2270, 23.2320, and 23.2510 for
normal category airplanes. The FAA also received comments seeking
clarification of the term ``some damage'' in the definition of CEL. The
allowance for some damage to the aircraft exists in the 14 CFR 23.2000
definition of CSFL. For the Archer Model M001, this allowance was moved
to the definition for CEL. The intent is that, although there may be
aircraft damage, the occupants remain protected to the extent that
egress may still be achieved following the landing.
The FAA received several comments requesting clarity on the meaning
of ``loss of thrust'' and ``critical loss of thrust'' in AM1.2000 and
throughout the airworthiness criteria. These terms were inherited from
the existing airworthiness standards used to create the proposed
airworthiness criteria. The FAA agrees that the ``loss of thrust'' term
is inadequate for the Model M001, which incorporates distributed
propulsion with an integrated flight and propulsion control system.
Historically, this terminology was used to convey an assumed complete
engine failure because of the critical nature that engines, propellers,
and transmissions provided regarding continued flight or CSFL
capability. With the advent of distributed propulsion, the underlying
assumptions of design features, mitigations, and substantiation of
capability under endurance testing established within the legacy
requirements are no longer valid, requiring revision.
Distributed propulsion with an integrated flight and propulsion
control system adjusts the aircraft's flight path using aerodynamic
and/or propulsive forces. In addition to addressing the complete loss
of thrust at any individual location and its effects, the design must
address additional failures from the flight and propulsion control
system that may inadvertently generate more or less thrust than
commanded by a pilot. For powered-lift with tilting nacelle designs
like the Model M001, the design must also address the possibility of
any given nacelle to fail in an orientation that does not match its
commanded position, and account for the subsequent thrust vector that
results. In part, some of these failures are identified through the
system safety process. However, other considerations exist outside of
that process that are necessary for identifying other critical
failures. As such, the FAA has included a definition of ``critical
change of thrust'' to address the thrust's magnitude and orientation.
Critical change of thrust may consist of more than one condition
depending on what flight conditions it adversely affects (performance,
handling qualities, or both). A critical change of thrust will require
a dedicated assessment encompassing all the above elements.
Further, the proposed definition for ``loss of power/thrust'' was
not adopted in these final airworthiness criteria. Since this term was
only used in the proposed AM1.2105(g), the final AM1.2105(g)
requirement was rewritten to directly incorporate the previous ``loss
of power/thrust'' definition language and clarify that the condition
represents any scenario in which commanded thrust is insufficient to
ensure CSFL, regardless of cause.
The FAA also received recommendations to modify the proposed
``source of lift'' definition to use terminology consistent with the
powered-lift definition in 14 CFR part 1. The FAA agrees and has
revised this definition to align with the powered-lift definition more
closely.
One commenter requested the FAA clarify the meaning of
``predominately'' and what was meant by ``combination'' in the
definition of ``source of lift.'' The FAA has changed ``predominantly''
to ``principally'' in AM1.2000(b)(3) of these final criteria, as the
term ``principally'' is used in the part 1 definitions of powered-lift
and rotorcraft. The FAA intended for the definition of ``source of
lift'' in AM1.2000(b)(3) to be aligned with the existing regulatory
definitions of powered-lift and rotorcraft. The FAA intends the term
``combination'' to capture instances where the sources of lift involve
both engine driven lift devices (e.g., rotors) and non-rotating
airfoils (e.g., fixed wings), generally in a manner in which the
balance between the two is varying during transition from wing-borne
flight to thrust-borne flight and vice-versa. The FAA received a
comment asking to replace the term ``hover'' with ``taxi'' in the
listed phases of flight in AM1.2000(b)(2). The FAA disagrees as the
term ``hover'' refers to an airborne flight condition and ``taxi''
refers to movement while on the ground. Another commenter requested
that the FAA add ``taxi'' to the criteria, since the term is also used
in AM1.2225. The FAA disagrees as the term ``ground operations'' in
AM1.2000(b)(2) includes taxi operations. No changes were made as a
result of this comment.
The FAA received comments asking that the terms ``shutdown,''
``start,'' ``restart,'' and ``idle'' be defined for electric engines.
The FAA disagrees. The FAA intends that these terms have the same
meaning as for existing engine technology, but recognizes that there
may be some differences based on the specific design of the Model M001
and its engine operations. The FAA received a comment questioning the
applicability of part 33 requirements that used the term
``rotorcraft.'' Upon further review, the FAA found similar issues with
the references to ``airplane'' within part 33 and part 35. The FAA
agrees with the concern and updated AM1.2000(c) to clarify that part 33
and part 35 requirements that use the terms ``airplane'' and
``rotorcraft'' mean ``aircraft.'' This also prompted the FAA to remove
the inappropriate reference to typical airplane installations in Sec.
35.37(c)(2). The FAA also received a comment questioning the use of the
term ``of this part'' in part 33. The FAA agrees; the revision to
AM1.2000(c) also clarifies that ``this part'' means ``these
airworthiness criteria'' when used in part 33 and part 35 requirements.
Lastly, the FAA added a definition for the term ``local events'' in
response to comments requesting clarification of this term as used in
requirements in subparts H and I.
Applicable Criteria
The FAA proposed applicable criteria by determining the appropriate
airworthiness requirements that apply to the Model M001 powered-lift.
These criteria are tailored to the powered-lift's design, including its
engines and propellers, as well as its construction, intended use, and
suitability for compliance with operational requirements.
EASA, GAMA, Lilium, Overair, TCCA, Vertical Aerospace, Volocopter,
and an anonymous commenter requested the FAA remove sections and terms
from the proposed airworthiness criteria that do not specifically apply
to the Model M001 design. The FAA
[[Page 45947]]
agrees and did not adopt the following in these final airworthiness
criteria as they were not specifically applicable to the Model M001:
AM1.2225(c);
AM1.2240(b) (a new AM1.2240(b) has been added);
Sec. 23.2310;
AM1.2320(d), (e) (the remaining requirements of AM1.2320
have been transitioned to Sec. 23.2320);
AM1.2325(h);
Sec. 23.2420;
Sec. 23.2435;
Sec. 23.2530(e);
AM1.2540; and
Sec. 35.43.
The following phrases were not adopted in these final airworthiness
criteria as they are not specifically applicable to the Model M001
design:
AM1.2400(a): ``or provides auxiliary power to the
aircraft;''
AM1.2405(a), (b), (c): ``reverser system;''
AM1.2430(a)(3): ``and auxiliary power unit;'' and
AM1.2430(c), (c)(1), (c)(3): ``refilling or.''
The FAA received comments that questioned the inclusion of HIRF and
lightning requirements for aircraft approved for Instrument Flight
Rules (IFR) operations. The requirements are conditional for IFR
approved designs. The FAA found it prudent to specify basic design
requirements for HIRF and lightning based on the expectation that
future design modifications could include an IFR approval. However,
additional design and installation requirements beyond those specified
in these airworthiness criteria would be needed for the aircraft to be
approved to operate under IFR.
Lastly, the FAA received numerous comments noting that the airplane
levels prescribed by Sec. 23.2005 should no longer be referenced in
these criteria, as they apply to conventional airplanes and not to a
powered-lift. The FAA agrees and has revised the airworthiness criteria
accordingly.
Technical Areas in General Order of the Airworthiness Criteria Sections
Aircraft Performance, Handling, and Control
The FAA received and reviewed comments from Alaka'i, Airbus, ALPA,
ANAC, ASD-Europe, EASA, GAMA, Leonardo, Lilium, Odys, Overair, Rolls-
Royce, Skydrive, TCCA, Vertical Aerospace, Volocopter, and an anonymous
commenter requesting the FAA revise, remove, or clarify proposed
airworthiness criteria related to aircraft performance, handling, and
control for the Model M001.
The FAA received a comment noting the inconsistent use of terms
when referring to the applicable atmospheric references proposed in
AM1.2105, AM1.2115, and AM1.2130. Under AM1.2105(a), performance
requirements at atmospheric conditions must be applied to all
requirements in Subpart B unless otherwise prescribed, including
AM1.2115 and AM1.2130. The FAA modified AM1.2115 and AM1.2130 to
include fixed performance parameters for takeoff and landing,
respectively; however, this does not negate the requirement to account
for atmospheric conditions as denoted in AM1.2105(a). One commenter
suggested adding ``at sea level'' to AM1.2105(a), consistent with the
language for levels 1 and 2 low-speed airplanes in part 23. The FAA
disagrees. AM1.2105(a) as proposed achieves the intended safety
objectives and aligns the airworthiness criteria with the appropriate
level of safety intended by utilizing appropriate standards from both
parts 23 and part 27, with revisions specific to the Model M001. The
FAA did not modify AM1.2105(a) as a result of this comment.
The FAA received comments that stated a concern that proposed
AM1.2105(b)(1) inadvertently limits airport altitudes to 10,000 ft. The
FAA agrees and has changed the airworthiness requirement to develop
performance data to the maximum altitude for which certification is
being sought.
The FAA also received a comment requesting clarification whether
the 10,000 feet specified in AM1.2105(b)(1) should be expressed in
either mean sea level or above ground level. The language in AM1.2105
is consistent with the existing airworthiness standard Sec. 23.2105
and is referenced to the altitude above sea level. No change was made
as a result of this comment.
One commenter requested revision of AM1.2105(c), stating the rule
is too vague and recommending that a minimum crosswind limit be
established similar to parts 27 and 29. The FAA agrees with the need
for a minimum crosswind limit and revised AM1.2135(a)(6) in response to
similar comments to specify a minimum of 17 knots all azimuth
capability. The FAA did not change AM1.2105(c) as a result of these
comments.
The FAA received comments about AM1.2105(f) expressing confusion
about what the phrase ``critical loss of thrust'' means relative to a
powered-lift design of the Archer M001 type.'' As mentioned previously,
the FAA replaced the phrase ``critical loss of thrust,'' with a new
term ``critical change of thrust'' which is defined in AM1.2000.
Several commenters noted inconsistent utilization of the term
``flight envelope'' and requested clarification. One such instance was
identified in AM1.2135(a), where the criteria referenced an ``operating
envelope.'' The FAA's intent was not to imply this flight envelope was
different from others referenced in these airworthiness criteria. To be
consistent, the FAA has generally replaced ''operating envelope'' with
``approved flight envelope'' where applicable such as AM1.2105(f) and
AM1.2135(a), except for AM1.2425(b) and AM1.2710(d), where the proposed
requirements define operating envelopes specific to the engine.
Additionally, the FAA included AM1.2135(a)(7) to incorporate the
steepest approach gradient within the approved flight envelope.
The FAA received several comments requesting clarification of the
new term ``loss of power or thrust'' defined in proposed AM1.2000(b)(4)
and used in proposed AM1.2105(g) to specify the required level of
safety after a condition when the aircraft can no longer provide
commanded power or thrust required for CSFL. This proposed term
generated confusion with similar terminology referring to loss of
thrust in other sections of the criteria. The FAA agrees that
clarification is necessary and therefore has not adopted the ``loss of
power/thrust'' definition in final AM1.2000. The FAA has also revised
AM1.2105(g) by replacing the term ``loss of power or thrust'' with the
definitional language from proposed AM1.2000(b)(4).
Several commenters asked for clarification on AM1.2105(g) and the
use of system safety or operational mitigations as the compliance
showing. The FAA modified AM1.2105(g) to provide additional clarity.
Revised AM1.2105(g) is intended to assure that in the event of cockpit
mismanagement, energy exhaustion, improper maintenance, or other
failures, a controlled emergency landing can be achieved. AM1.2105(g)
establishes safety objectives and the FAA's acceptance of a specific
means of compliance is beyond the scope of these airworthiness
criteria.
A commenter asked for clarification on AM1.2105(g) as to whether a
conventional forward landing would be an acceptable mitigation for loss
of power or thrust. A conventional forward landing may be acceptable if
the aircraft is capable of a controlled emergency landing in that
configuration. No
[[Page 45948]]
changes were made as a result of this comment.
The FAA received comments requesting that the FAA more explicitly
state that the speed for thrust-borne flight in AM1.2110 and AM1.2150
may include hover. The minimum safe speed determined in AM1.2110 must
cover all phases of flight (including hover) and all sources of lift,
and AM1.2150 uses that minimum safe speed. As such, no change to the
criteria is necessary.
The FAA also received a request to revise AM1.2110 to require
minimum safe speed for ``each flight condition and configuration''
instead of only for each flight condition. The FAA disagrees. The
phrase ``flight condition'' includes the aircraft configuration, phases
of flight, and the sources of lift. No change to the criteria is
necessary.
Several commenters stated that the proposed airworthiness criteria
for takeoff performance in AM1.2115, climb performance in AM1.2120, and
landing performance in AM1.2130 do not establish sufficient minimum
performance requirements to meet the public's expectations and levels
of safety. One commenter recommended rewording paragraph (b) of
AM1.2115, AM1.2120, and AM1.2130 to require the applicant to account
for a range of engine or distributed propulsion system failures instead
of accounting for loss of thrust.
As explained previously, the FAA recognizes the need to clarify the
difference in requirements for ``essential'' and ``increased''
performance levels as defined in AM1.2000(b)(1) for the Model M001 with
respect to the takeoff, climb, and landing performance criteria of
AM1.2115, AM1.2120, and AM1.2130, respectively. The FAA has revised
these performance requirements to include scenarios for all engines
operating and for critical changes of thrust. As revised, AM1.2115,
``Takeoff performance'' addresses all engines operating, as well as
critical change of thrust conditions, for both essential and increased
performance levels. Essential performance level requirements ensure all
engines operating takeoff capability and the capability to perform
either a safe stop or safe landing following a critical change of
thrust. Increased performance, while similar for safe stops, defines
the requirements for continued takeoff following a critical change of
thrust, including the capability to continue the climb and then
subsequently achieve the configuration and airspeed specified for
increased performance in AM1.2120, ``Climb Performance.''
The FAA revised AM1.2120 to establish targets for both essential
and increased climb performance for all engines operating, as well as
after a critical change of thrust, as defined in AM1.2000. The FAA
developed essential and increased climb performance requirements with
all engines operating using part 23 requirements. Essential performance
also requires that the applicant assess critical change of thrust
impacts on takeoff and climb performance capabilities. Increased
performance after a critical change of thrust defines minimum criteria
utilizing part 23 and part 27 Category A climb requirements, dependent
on the takeoff flight path and sources of lift defined in AM1.2000
along that path.
Multiple commenters requested clarity on where glide and
autorotation performance are captured. The FAA added AM1.2120(e), which
requires the applicant determine the performance for gliding or
autorotation.
The FAA received a number of comments noting the lack of
specificity in proposed AM1.2130. The comments noted that AM1.2130 was
overly vague and did not provide enough substantive detail to support
the intent of the criteria. The FAA agrees and has revised AM1.2130 to
ensure the level of safety and capability for essential and increased
performance for takeoff in AM1.2115 is consistent with the level of
safety and capability for essential and increased performance for
landing in AM1.2130. Landing under AM1.2130 now contains requirements
for both essential and increased performance levels, such that the
aircraft must be able to make a landing upon a critical change of
thrust. For increased performance, the FAA has also included a minimum
criterion to safely transition to a balked landing condition following
a critical change of thrust.
The FAA received a comment that determining the performance for all
potential partial loss of power conditions in proposed subpart B may be
impractical. The FAA agrees. As mentioned previously, a new term,
``critical change of thrust'' has been defined in AM1.2000 to identify
the most critical thrust-related failure condition(s) for the Model
M001 powered-lift. This term requires consideration of the most adverse
effect on performance or handling qualities. The FAA modified AM1.2115,
AM1.2120, AM1.2125, and AM1.2130 to use this new definition of critical
loss of thrust.
A commenter requested clarification on the phrase ``applicable
sources of lift'' in AM1.2135(a)(2). During a specific phase of flight,
an aircraft design may only allow for a singular source of lift during
that phase of flight. In other phases of flight, one or more sources of
lift may be possible. Therefore, ``applicable sources of lift'' refers
to only those allowable by the aircraft design. No changes were made as
a result of the comment.
Multiple commenters requested the FAA establish an additional limit
flight envelope which would establish the controllability limits of the
aircraft. The FAA does not agree with this request. The FAA intended
proposed AM1.2135 to establish the regulatory requirement for
controllability that is used to define the approved flight envelope.
The FAA recognizes that excursions outside of the aircraft's approved
flight envelope can occur and must be considered from a safety
perspective. The FAA has replaced the proposed requirement of Sec.
23.2160(a) with new AM1.2160 to address speed excursions beyond the
approved flight envelope.
The FAA received multiple comments requesting the FAA utilize the
multiple flight envelope concept in EASA's SC-VTOL, in lieu of the
proposed minimum safe speed requirement in AM1.2110. The commenters
stated that the FAA's proposed requirement may be appropriate for wing-
borne flight, but it is not appropriate for other aircraft
configurations. The FAA determined that the establishment of a minimum
safe speed and an approved flight envelope establishes a level of
safety for the Model M001 that is consistent with the safety levels as
established in parts 23 and 27.
The FAA also received comments seeking clarification on atmospheric
effects, scoping, and sources of lift in regard to AM1.2110. The intent
of that requirement is to address flight conditions in normal operation
considering the most adverse conditions, which includes adverse
atmospheric effects. Accordingly, no change to this requirement is
necessary. Establishment of minimum safe speeds in regard to specific
sources of lift will be established through the issue paper process.
Regarding controllability, the FAA received comments asking the FAA
to adopt the requirement in Sec. 23.2135(a)(3), to address ``likely
reversible flight control or propulsion system failure,'' instead of
proposed AM1.2135(a)(3), which requires addressing ``likely flight-
control or propulsion-system failure.'' Commenters further clarified
that they believed flight controls are fully addressed by the proposed
requirement that the Model M001 comply with
[[Page 45949]]
Sec. 23.2510. The FAA disagrees and determined that specific
airworthiness criteria for controllability are needed to address the
integration of the advanced flight-control system and the propulsion-
system. In addition, AM1.2135(a)(3) is to ensure that likely failures
not included in the system safety process of Sec. 23.2510 are
addressed and that failures that are included have an adequate handling
quality assessment which is outside the scope of Sec. 23.2510. No
changes were made as a result of these comments.
The FAA also received a comment requesting that the flight control
system be subjected to the same requirements found in AM1.2705,
AM1.2710, AM1.2713, and AM1.2727 for the engine control system due to
the highly integrated nature of these systems. The FAA disagrees as the
engine control system and flight control system are not integrated into
one system. No changes were made as a result of this comment.
One commenter asked the FAA to remove AM1.2135(a)(5) because the
requirements of proposed Subpart F would sufficiently mitigate this
hazard. The FAA disagrees. AM1.2135(a)(5) requires controllability
evaluation using approved flight test methods of compliance. The
requirements in Subpart F, which apply to equipment, do not adequately
address this concern. No changes were made as a result of this comment.
The FAA received a comment to modify AM1.2135(a)(5) to remove the
phrase ``not shown to be extremely improbable.'' The FAA disagrees.
Removing this phrase would require the applicant to address all failure
conditions regardless of their probability. The FAA included this
phrase to limit the cases where handling qualities are evaluated to
those conditions not shown to be extremely improbable to limit the
applicant's burden. No changes were made as a result of this comment.
Several commenters requested that a minimum level of safety be
established with respect to proposed AM1.2135(a)(6), which requires
that the aircraft can land safely in wind conditions. Multiple
commenters questioned whether AM1.2135(a)(6) was only applicable to
thrust-borne flight. The FAA concurs that a minimum level of safety
should be defined and has amended AM1.2135(a)(6) to contain a more
prescriptive all-azimuth minimum wind speed requirement of 17 knots.
This minimum wind limit is applicable to the thrust-borne operations
and is consistent with requirements for parts 27 and 29 rotorcraft.
The FAA received a comment that the term ``loading'' in proposed
AM1.2135(a)(1) needed to be revised to include energy level
considerations (i.e., degraded or low battery). Energy level
considerations are covered under AM1.2135(a)(3), (a)(5), and (b), which
address propulsion system failures, flight control system operating
modes and critical control parameters such as limited-control power
margins, respectively. Propulsion system failures include the
electrical distribution and batteries. The same commenter proposed
adopting a new requirement to address a rolling takeoff in maximum
crosswind. The situation noted by the commenter is already addressed by
AM1.2135(a)(2), which covers all phases of flight (e.g., takeoff for
the approved flight envelope including crosswinds). No changes were
made as a result of these comments.
Multiple commenters asked for clarity on the phrases ``critical
control parameters'' and ``limited control power margins'' in
AM1.2135(b). The phrase ``critical control parameters, such as limited
control power margins'' is intended to capture parameters or limits in
which the aircraft is control or performance limited. The applicant
must define these parameters as they apply to their unique design. No
changes were made as a result of these comments.
The FAA received a comment recommending that ``change from one
flight condition to another'' be replaced with ``transition from one
flight condition to another'' in AM1.2135(c). The FAA agrees and has
updated AM1.2135(c) accordingly.
Several commenters stated that the language utilized from part 23,
pre-amendment 23-64, in the development of proposed AM1.2145 did not
provide appropriate granularity between static and dynamic stability
and sources of lift for a powered-lift. The FAA agrees and has revised
the requirements in AM1.2145 to account for the difference in stability
requirements that arise between wing-borne, semi-thrust-borne, and
thrust-borne flight for the Model M001.
The FAA received comments asking the FAA to provide specific likely
failure cases to be considered in addition to more detailed control
feel requirements in proposed AM1.2145(a). The FAA partially concurs
with these comments. The intent of AM1.2145(a) is for the applicant to
identify likely failures that may be encountered in service that are
not addressed by system safety analysis; those could include mechanical
or other single point failures. The FAA has revised the language in
AM1.2145(a) to improve clarity but did not concur with the commenters'
request to identify specific failure conditions, including detailed
control feel requirements.
The FAA also received a comment seeking clarity on the term
``unstable'' in AM1.2145(b). The FAA revised proposed AM1.2145(b) (now
AM1.2145(c), due to changes discussed previously) to clarify that the
intent is to ensure dynamic stability characteristics. The FAA intends
``unstable'' to mean the same as is stated in the criteria: that the
characteristics do not increase the pilot's workload or otherwise
endanger the aircraft and its occupants.
The FAA also received comments regarding aerobatics and whether
such proposed criteria are applicable to this class of vehicle or if
instead the criteria should be better tailored to Archer's design. The
FAA agreed and revised AM1.2145 and AM1.2150 accordingly with the
recognition that Archer is not seeking approval for aerobatics for the
Model M001.
The FAA received a comment that proposed AM1.2150 may be adequate
for wing-borne operation but not thrust-borne operation. The FAA agrees
and has revised AM1.2150 to address all sources of lift.
The FAA also received a comment questioning the terminology
``critical loss of thrust'' in proposed AM1.2150(b). The FAA agrees
this term was inappropriate for an aircraft capable of vertical takeoff
and landing operations because it requires a hazardous test condition
that would result in an initial adverse environment, which was not the
intent. The FAA has updated AM1.2150(c) (previously proposed
AM1.2150(b)) to replace ``critical loss of thrust'' with ``sudden
change of thrust'' to remove this hazardous condition and to
distinguish it from the term ``critical change of thrust'' defined in
AM1.2000. The FAA intends the term ``sudden change of thrust'' to refer
to short-term commanded thrust changes, whether directly by the pilot
or from the flight control system in normal operation. The FAA received
comments on proposed AM1.2150 that a maximum speed limitation may be
necessary to prevent loss of control on a powered-lift. The FAA agrees
with the commenters, but because AM1.2150 relates to minimum safe speed
requirements, the FAA has revised AM1.2160 to include this safety
requirement in AM1.2160(b).
The FAA received a comment requesting clarification on the
applicability of Sec. 23.2155. The commenter questioned the necessity
for
[[Page 45950]]
this requirement with the assumption that powered-lift do not taxi
under their own power. The FAA disagrees that this requirement should
not be adopted as proposed, as the Model M001 has the ability to taxi.
No changes were made as a result of the comment.
The FAA also received a comment on proposed AM1.2140(c) suggesting
the removal of ``multi-engine.'' The commenter stated that because the
Model M001 is a multi-engine aircraft, including this term adds no
value and may create confusion. The FAA agrees and did not adopt the
reference to ``multi-engine aircraft.''
Finally, the FAA received several comments about AM1.2140(c)'s use
of the language, ``loss of thrust not shown to be extremely
improbable'' in the context of trim system requirements. As mentioned
previously, a new term, ``critical change of thrust'' was defined in
AM1.2000 to provide an equivalent term adapted to the Model M001
design. The FAA modified AM1.2140(c) to use ``critical change of
thrust'' as a result.
One commenter noted that proposed AM1.2140(a) should not be limited
to just cruise flight. The FAA agrees and has removed the reference
limiting the requirement to cruise flight. Additionally, commenters
expressed a concern that normal phases of flight utilized in proposed
AM1.2140(a) and the flight conditions identified in proposed
AM1.2140(b) may create some confusion. The FAA agrees and has revised
the language in AM1.2140(a) to specify ``normal operations'' instead of
``normal phases of flight.''
One commenter requested the FAA change the phrase ``level flight''
to ``cruise'' in AM1.2140(b)(2). AM1.2140(b)(2) references flight
conditions and not phases of flight, and therefore ``level flight'' is
appropriate. The commenter also requested the FAA add ``hover'' to
AM1.2140(b). Hover does not have a longitudinal component, and as such
trim in that axis is not applicable. Adjustments of trim may not apply
any discontinuities as identified in AM1.2140(c). No changes were made
as a result of these comments.
The FAA received comments concerning the use of the term ``trim''
in proposed AM1.2140 and questioning its appropriateness with fly-by-
wire control systems that do not use traditional trimming arrangements.
The FAA finds the requirements in AM1.2140 applicable because the Model
M001 fly-by-wire flight controls may implement a trimming function
rather than conventional trim device tabs or bias springs. Such a
function would be equivalent to a trim or auto-trim device. No changes
were made as a result of these comments.
One commenter requested that the FAA replace the term ``primary
flight controls'' in proposed AM1.2140(a) and (b) with the term
``inceptor.'' The FAA disagrees. Although inceptors and effectors may
fall under the term ``primary flight controls,'' the FAA does not find
this change necessary as it prescribes a specific implementation of
technology. No changes were made as a result of this comment.
Icing
The FAA received and reviewed comments from Airbus, ALPA, EASA,
GAMA, Overair, and TCCA requesting the FAA revise, remove, or clarify
proposed airworthiness criteria related to flight into known icing
(FIKI) conditions as well as inadvertent icing encounters.
Specifically, commenters requested the FAA explain why references to
icing conditions requirements were excluded, revise the level of
prescriptiveness of the criteria, and remove FIKI requirements because
the Model M001 is not seeking FIKI approval at this time. At the same
time, the FAA received comments requesting the FAA include more
specific requirements for FIKI conditions.
Based on numerous comments received noting that Archer does not
seek approval for FIKI on the Model M001 at this time, the FAA did not
adopt proposed AM1.2165(a). Proposed AM1.2165(b) and (c), which address
inadvertent icing encounters, remain applicable to the Model M001, and
have been renumbered to AM1.2165(a) and (b), accordingly. AM1.2415 is
similarly intended to capture any aircraft icing during an inadvertent
encounter that adversely affects powerplant operation.
The FAA received comments requesting the FAA include requirements
for recirculating snow and accumulation of ice and snow, because
smaller rotors and airfoils, such as those on the Model M001, are known
to be susceptible to the effects of snow and icing. The FAA agrees with
concerns regarding the effect of scale on ice accretion, but finds they
are addressed by proposed AM1.2165(b) (AM1.2165(a) in these final
criteria) for an inadvertent icing encounter. Recirculating and
accumulation of snow are foreseeable conditions addressed by Sec.
23.2415(a) for engine operation and by AM1.2600(a) for flightcrew
visibility considering accumulations on the windshield due to
recirculating snow.
The FAA received requests to remove proposed AM1.2165(b) since the
Model M001 powered-lift is not seeking FIKI approval. The FAA does not
agree, as proposed AM1.2165(b) (AM1.2165(a) in these final criteria)
addresses inadvertent icing encounters, not FIKI. The relatively low
revolution speed and resulting low centrifugal acceleration effect on
ice shedding capability, as well as the effect of increased torque on
electric engines, need to be addressed in an inadvertent icing
encounter.
Lastly, the FAA received several comments on proposed AM1.2165(a),
requesting that the FAA explain why the reference to the icing
conditions defined in appendix C of part 25 was excluded from these
airworthiness criteria. Because Archer is not seeking FIKI approval at
this time, the FAA determined in response to comments from EASA, GAMA,
and Overair, that proposed AM1.2165(a) should not be adopted in these
final airworthiness criteria. Should Archer seek icing certification
through an amendment to their type certificate after initial type
certification, appropriate icing standards will be defined as part of
that project. This will allow Archer to seek a standard that reflects
their operating limitations and specifics of their design.
Structural Design Loads
The FAA received comments from Airbus, ALPA, EASA, Rolls-Royce, and
TCCA requesting the FAA revise, remove, or clarify proposed
airworthiness criteria related to structural design loads for the Model
M001, including vibration and buffeting, flight modes, and wing borne
vs. thrust-borne design loads.
The FAA received a comment to modify Sec. 23.2215(a) to cover the
whole operational envelope of the aircraft. The FAA does not agree. The
objective of this criteria covers the structural design envelope, which
may exceed the operational envelope requirement recommended by the
commenter. No changes were made as a result of this comment.
A commenter recommended the FAA include the structural requirement
for vibration and buffeting and harmonize with EASA's SC-VTOL.2215(b)
for powered-lift, by adding ``Vibration and buffeting must not result
in structural damage up to dive speed, within the limit flight
envelope'' to Sec. 23.2215.
The FAA agrees that vibration and buffeting must not result in
structural damage, but the FAA does not agree to use the SC-
VTOL.2215(b) language. The FAA finds that EASA's scope for vibration
and buffeting in SC-VTOL is not sufficient for powered-lift. The FAA
instead moved the proposed requirement to comply with Sec. 23.2215 to
AM1.2215(a) and added a new paragraph (b), which states, ``There
[[Page 45951]]
must be no vibration or buffeting severe enough to result in structural
damage, at any speed up to dive speed, within the structural design
envelope, in any configuration and power-setting.''
Two commenters requested the FAA clarify the transitional flight
mode for engine-driven lifting-device assembly provisions per
AM1.2225(d). The commenters pointed out that the structural loads
requirements for this special class of aircraft include loads resulting
from the transitional flight phase that are not considered under
loading conditions in parts 23 and 27. Specifically, the commenters
were concerned that propellers, when repositioned in-flight relative to
the aircraft primary axis, may introduce unique load cases relative to
conventional propeller loads that would impact the static strength
evaluations. The commenters recommended the FAA capture requirements
for loads in all phases of flight by revising AM1.2225(d). One
commenter requested revising AM1.2225(d) to read ``Engine-driven
lifting-device assemblies, considering loads resulting from flight
(including transitional flight mode) and ground conditions, as well
limit input torque at any lifting-device rotational speed.'' Another
commenter requested revising AM1.2225(d) to read ``Engine-driven
lifting device assemblies, considering loads resulting from flight and
ground conditions, limit input torque at any lifting-device rotational
speed as well as propeller holding or clocking (locking) conditions of
applicable.''
The FAA agrees that all powered-lift flight configurations need
clarification for the calculation of structural design loads for
transitional flight phases. The FAA also recognizes that changes in
propeller ``disk'' orientation during flight will affect aircraft loads
resulting from the aerodynamic influence of the propellers on the
aircraft. Similarly, the FAA considers it likely that aircraft
aerodynamics loads will influence the propeller aerodynamic loads.
Therefore, the FAA concluded that proposed AM1.2200 Structural Design
Envelope should be revised instead of AM1.2225 (as suggested by the
commenters) to include, ``Thrust[hyphen]borne, wing[hyphen]borne, and
semi[hyphen]thrust[hyphen]borne flight configurations, with associated
flight load envelopes.'' The FAA added AM1.2200(g) accordingly.
Multiple commenters asked for clarity on the requirements in
AM1.2225(d) and whether the intent of that criteria could be shown
through means of compliance with AM1.2225(a). The FAA disagrees.
AM1.2225(a) is specific to loads for the engine mount, whereas
AM1.2225(d) is specific to lifting device assemblies.
Multiple commenters requested the FAA provide clarification in
AM1.2200(b) with respect to appropriate design maneuvering load factors
for powered-lift designs. The intent of AM1.2200 is to describe the
various design envelopes that must be considered by the applicant in
the loads analysis. No changes were made as a result of these comments.
One commenter requested that the FAA define the term
``sufficiently'' in AM1.2200(a)(1) and (2). As explained in the notice
of proposed criteria, the FAA based proposed AM1.2200 on Sec. 23.2200,
with revisions to address the powered-lift structural design envelope.
The terms ``be sufficiently greater'' in AM1.2200(a)(1) and ``provide
sufficient margin'' in AM1.2200(a)(2) have the same meaning, and will
be applied to the Model M001 in the same manner, as in Sec.
23.2200(a)(1) and (2). No changes were made as a result of the comment.
EASA stated that AM1.2200(e), which proposed to require that the
applicant account for each critical altitude up to the maximum
altitude, does not consider redistribution of loads if deflections
under load would significantly change the distribution of external or
internal loads. EASA also requested the FAA revise AM1.2200(e) similar
to EASA SC-VTOL.2200(e). The FAA does not concur, as the critical
altitude and redistribution of loads requirement in SC-VTOL.2200(e) is
already captured by AM1.2200(e) and Sec. 23.2210. No changes were made
as a result of this comment.
The FAA received multiple comments questioning the requirement to
use service history in the development of the design load maneuvering
factors in AM1.2200(b), since the Model M001 has no service history.
One commenter requested the FAA add specific language to the
airworthiness criteria that points to using service history from
existing normal category aircraft. The FAA agrees that the service
history utilized in this showing should come from service experience
from both rotorcraft and small airplane service history. However, the
FAA disagrees that a change to the airworthiness criteria is necessary.
One commenter recommended the FAA revise proposed AM1.2225 to be
more generic by specifying source of loads for any relevant structural
components, and not only the components specific to the Model M001. The
FAA disagrees, as these airworthiness criteria are specific to the
applicant's design.
Structures
The FAA received and reviewed comments from ASD-Europe, Airbus,
EASA, GAMA, Leonardo, Lilium, Overair, Odys, TCCA, Volocopter, and an
anonymous commenter requesting the FAA revise, remove, or clarify
proposed airworthiness criteria related to aircraft structure for the
Model M001.
Several commenters suggested adding the level 4 airplane
requirements for damage tolerance in Sec. 23.2240(b) to AM1.2240 to
incorporate damage tolerance principles. The FAA partially concurs with
the recommendations of the commenters and has clarified AM1.2240(b)
consistent with the FAA's long-standing policies regarding use of fail-
safe methodology in conjunction with damage tolerance inspections.
Fail-safe methodologies, also referred to as safety-by-design,
incorporate multi-load-path structure (i.e., redundant load paths) to
act as back-up structure should any one of the original load paths
(i.e., fail-safe structure) fail. Damage tolerance (i.e., safety-by-
inspection) is a property of structure relating to its ability to
sustain defects safely until those defects can be detected.
The FAA does not agree that adoption of Sec. 23.2240(b) is
necessary or appropriate, as this requirement is specific to airplanes
that meet the definition in Sec. 23.2005 for a Level 4 airplane that
can carry 10-19 passengers. The Sec. 23.2240(b) requirement for Level
4 airplanes was derived from Sec. 23.574 at amendment 23-48 and
excluded the option to use fail-safe methodologies for commuter
category airplanes (Level 4). In addition, Sec. 23.574(a) requires the
use of damage tolerance and allows the use of safe-life in Sec.
23.574(b) only when damage tolerance is found to be impractical.
Damage tolerance is one available option to use when complying with
AM1.2240(a), along with the options to use safe-life and fail-safe
methodologies, provided the fail-safe option relies on damage tolerance
or safe life as stipulated in numerous FAA policies including AC 27-1B,
``Certification of Normal Category Rotorcraft''; AC 23-13A, ``Fatigue,
Fail-Safe, and Damage Tolerance Evaluation of Metallic Structure for
Normal, Utility, Acrobatic, and Commuter Category Airplanes''; and AC
91-82A, ``Fatigue Management Programs for In-Service Issues.'' The FAA
notes further that the intent of adding AM1.2240(b) to these final
criteria was to incorporate inspection when the fail-safe method is
used. Incorporating inspections addresses long-standing and known
deficiencies with fail-safe methodologies on all part
[[Page 45952]]
23 airplanes, as clarified in the preamble to the Notice of Proposed
Rulemaking (NPRM) for amendment 23-64, in which the FAA identified
potential shortcomings in the ability to detect all possible failure
scenarios and ensure that all structural failures would be immediately
obvious and corrected before further flight. The intent of structural
durability requirements in both Sec. Sec. 23.2240(a) and 27.571 is to
use the appropriate application of safe-life or damage tolerance
principles to ensure that fail-safe structure maintains the required
safety margins without extended periods of operation with reduced
safety margins.
The FAA agrees with the commenters that further clarification on
the stipulations that govern the use of fail-safe methodologies should
be included in the Model M001 criteria to reiterate the FAA's
requirements in this regard. Consequently, the FAA has added a new
AM1.2240(b) that reflects the intent of Sec. 27.571(d) together with
amendment 23-64 and associated policies to incorporate damage tolerance
principles into powered-lift. The requirements in AM1.2240(b) will
mitigate deficiencies in the fail-safe option and will apply to the
Model M001 structure beyond those elements specifically identified by
Sec. 27.571. This is consistent with Sec. 21.17(b), which directs the
FAA to use the requirements from existing airworthiness standards, as
appropriate, to determine the level of safety for the aircraft.
Multiple commenters requested that the FAA align AM1.2240(c) with
EASA SC-VTOL.2240(d). The FAA notes that AM1.2240(c) is similar to SC-
VTOL.2240(d), although SC-VTOL.2240(d) refers to ``lift/thrust unit''
instead of ``engine.'' The EASA term ``lift/thrust unit'' includes the
engine and propeller or rotor assembly. This topic is an ongoing
discussion with foreign certification authorities. For the Model M001,
other rotating parts within the system, except for propeller blades or
rotors, should be evaluated using typical rotor burst methods,
including shielding where practical.
The FAA received a comment to move AM1.2240(c) to outside of
Subpart C Structures. The FAA disagrees as AM1.2240(c) is a requirement
specific to structural durability and is appropriately included in
AM1.2240, which is consistent with Sec. 23.2240. No changes were made
as a result of this comment.
Several commenters requested the FAA align Sec. 23.2250(c) with
the failure criteria in EASA SC-VTOL.2250(c). SC-VTOL.2250(c) contains
a requirement for Category Enhanced that a single failure must not have
a catastrophic effect upon the aircraft. The FAA's airworthiness
criteria do not contain requirements equivalent to EASA's ``Category
Enhanced'' requirements. However, the changes to AM1.2240(b) in these
final criteria require inspections capable of reliably detecting damage
before it leads to structural failure, thereby mitigating the
occurrence of catastrophic failures. The FAA also changed the proposed
requirement to comply with Sec. 23.2250(c) to new AM1.2250(c) to
require the applicant to prevent single failures from resulting in a
catastrophic effect upon the aircraft.
The FAA received a comment requesting the airworthiness criteria
include a requirement to address corrosion on metallic or semi-metallic
structure components resulting from high voltage difference of electric
potential. The FAA does not concur. AM1.2240(a) provides an appropriate
regulatory framework for addressing corrosion, as it embodies the
safety intent of the prescriptive requirements in pre-amendment 64
regulations Sec. Sec. 23.573 and 23.574, which directly address
corrosion, among other factors, in both composite and metallic
structure. This framework will be applied to the Model M001 in the same
manner as Sec. 23.2240 for normal category airplanes to address
corrosion resulting from any source, including high voltage difference
of electric potential. No changes were made as a result of this
comment.
Multiple commenters requested clarification on the lack of
environmental requirements in Sec. 23.2260(e), which applies to only
thermal effects. Environmental effects are addressed in Sec.
23.2260(a), and as such the FAA made no change as a result of these
comments.
Aeroelasticity & Aeromechanical Stability
The FAA received and reviewed a comment from Volocopter requesting
the FAA revise the proposed requirement to comply with Sec. 23.2245 to
provide further clarity regarding definitions used in the requirement,
specifically whether the probabilities of malfunctions that can affect
aeroelastic stability are aligned with those in EASA's SC-VTOL.2245.
The FAA has revised the proposed requirement as new AM1.2245 to
specifically require that component and rotating surfaces be free of
any aeroelastic instability under each appropriate speed and power
condition. Additionally, the FAA determined that the related issue of
aeromechanical stability should similarly be addressed but does not
consider it to be covered under the subject of aeroelasticity.
Therefore, the FAA created a new section AM1.2241, ``Aeromechanical
stability,'' incorporating requirements from rotorcraft airworthiness
standards, similar to ground resonance requirements in Sec. 27.241, to
address aeromechanical instabilities considered possible for the Model
M001 when operating in thrust-borne and semi-thrust-borne flight.
Flight Controls
The FAA received and reviewed comments from Airbus, ANAC, ASD-
Europe, EASA, GAMA, Leonardo, Lilium, Overair, and TCCA, requesting the
FAA revise, remove, or clarify proposed airworthiness criteria related
to flight controls for the Model M001.
The FAA received a comment stating that 14 CFR part 23 amendment
23-64's requirements for flight controls should be sufficient for the
Model M001 and the FAA should use those requirements. The FAA
disagrees. Part 23 at amendment 23-64 did not envision the type or
complexity of the design of powered-lift flight controls, such as those
on the Model M001. No changes were made as a result of this comment.
The FAA received several comments that raised concerns with the
suitability of proposed AM1.2300(b), which was developed from part 23
requirements for trim systems on normal category airplanes, for fly-by-
wire powered-lift with distributed propulsion. The FAA concurs with the
comments and modified proposed AM1.2300(b)(2) by replacing the specific
trim indications with a requirement that the trim systems and functions
provide information necessary for safe operation. The specific
indications listed in proposed AM1.2300(b)(2)(i)-(b)(2)(iv), which
summarize the prescriptive indications from 23.677(a) and ASTM F3232
section 4.4, may be used as means of compliance with final
AM1.2300(b)(2) if they are applicable, or they may be modified for the
novel implementation of trim functions on the Archer Model M001.
Commenters raised concerns over the flightcrew control margin
awareness for fly-by-wire flight control systems and recommended
including a requirement addressing this issue. The FAA concurs with the
comments and has added AM1.2300(a)(3) requiring the flightcrew to be
made suitably aware whenever the means of primary flight control
approaches the limits of control authority. For the context of this
airworthiness criteria, ``suitably aware'' indicates an appropriate
balance
[[Page 45953]]
between nuisance alerting and necessary operation.
Two commenters asked for clarification of the term ``indirect
flight-control systems'' in AM1.2300(c). The FAA agrees that this term
caused confusion. The FAA did not adopt this term and instead revised
AM1.2300(c) for clarity.
Several commenters stated that proposed AM1.2300 was overly
prescriptive because the requirements could be better addressed in
means of compliance and could conflict with automation in fly-by-wire
flight controls. In contrast, other commenters stated that proposed
AM1.2300 was insufficiently prescriptive and noted that regulations
need to explicitly guide applicants, especially for novel aircraft, and
specific requirements for awareness of reduced flight envelopes should
be provided.
The FAA considered these comments and revised proposed AM1.2300 to
be less prescriptive in instances where other requirements adequately
address the same safety objective. The FAA did not adopt the proposed
requirements in AM1.2300(c)(1), (c)(2)(i), and (c)(2)(iii) because they
were redundant with other requirements and were unnecessarily
prescriptive. The FAA added a more prescriptive requirement
specifically for control margin awareness in response to these
recommendations.
One commenter suggested a revision to the phrase ``the onset
characteristics of each protection feature is appropriate for the phase
of flight and type of maneuver'' in proposed AM1.2300(c)(2)(i). The FAA
notes there should be no discontinuous inputs into the flight control
system from envelope protection systems, but agrees that abrupt inputs
may be necessary in some situations (e.g., preventing stall in response
to an atmospheric disturbance). The FAA determined that this
requirement is adequately addressed by AM1.2300(a)(1) and therefore did
not adopt proposed AM1.2300(c)(2)(i).
The FAA received comments requesting clarification as to why the
term ``catastrophic'' is not used in proposed AM1.2300(c)(2)(iii) while
the term ``hazardous'' is used in proposed AM1.2710(f)(3). The FAA
reviewed the comments and determined that AM1.2300(c)(2)(iii) is
redundant to Sec. 23.2510, and therefore did not adopt proposed
AM1.2300(c)(2)(iii). For clarification, the FAA notes that AM1.2710
applies to the engines and addresses failure effects up to the
hazardous level, whereas Sec. 23.2510 applies to the aircraft and
addresses failure effects up to the catastrophic level. These safety
levels are intentionally different. No engine failure is allowed to
result in a catastrophic aircraft event. In addition, unlike Sec.
23.2510, AM1.2710 does not permit using a probabilistic means to manage
certain single-element parts that can fail and cause hazardous engine
effects.
A commenter recommended defining the term ``simultaneous limiting
event'' in AM1.2000. The FAA notes this term originates from unique
conditions applied to fly-by-wire systems with envelope protection. It
pertains to scenarios where multiple envelope limits could be exceeded.
The FAA does not consider it necessary to define this term in AM1.2000.
The FAA received a comment on Sec. 23.2305 requesting that the FAA
add a requirement for parking brakes. The FAA disagrees. Section
23.2305(b) requires a reliable means of stopping the aircraft. One
means to accomplish this may include a parking brake; however, the
applicant may propose other means. No changes were made as a result of
this comment.
Occupant System Design Protection
The FAA received comments from ALPA, EASA, GAMA, Lilium, Overair,
Rolls-Royce, and TCCA on occupant system design protection
requirements.
The FAA received comments seeking clarification on the proposed
inclusion of the ditching exclusion in Sec. 23.2315(a)(1) and a
comment that this contradicts the proposed requirement to comply with
Sec. 23.2310 for seaplanes and amphibians. The FAA concurs that the
language proposed caused confusion and has revised these proposed
requirements. The FAA did not adopt the proposed requirement to comply
with Sec. 23.2310 as it is not applicable to the Model M001. The FAA
maintained the scope of Sec. 23.2315 (now AM1.2315) specific to the
``cabin configured for takeoff or landing'' but did not adopt the
exclusion for ditching because the Model M001 is not seeking ditching
approval. One commenter requested that the FAA require shrouding on
propellers as these aircraft are planned to operate close to people or
property. The FAA does not concur with the comment. AM1.2315(a)(1),
originally proposed as Sec. 23.2315, requires that passenger doors are
not located where propellers would endanger persons using the door.
Operational requirements are also used to ensure safety of passengers,
ground crews, and property, as required for existing aircraft. No
changes were made as a result of the comment.
The FAA received comments regarding aerobatics and whether such
criteria are applicable to this class of vehicle or if the proposed
criteria for aerobatics should be removed. The FAA removed the proposed
requirement to comply with Sec. 23.2315(b) because the Model M001 does
not seek approval for aerobatics.
The FAA received comments asking the FAA to include the protection
of occupants in proposed AM1.2320(a)(2). Another commenter asked for
clarification of proposed AM1.2320(a)(2). Another commenter asked the
FAA to modify proposed AM1.2320(a)(2) to protect the pilot, flight
controls, and propulsion electrical power and control from propellers.
The intent of proposed AM1.2320(a)(2) (now Sec. 23.2320(a)(2) in these
final criteria) is to protect the pilot and systems so the pilot can
land the aircraft in the event of a propeller failure. Protection of
the occupants embarking and disembarking is required by AM1.2315.
Propulsion control is required by Sec. 23.2320(a)(2) as a part of the
flight controls on the Model M001. No changes were made as a result of
these comments.
Bird Strike
The FAA received and reviewed comments from Airbus, Alaka[revaps]i,
ALPA, ASD-Europe, EASA, GAMA, JCAB, Leonardo, Overair, TCCA, UKCAA,
Vertical Aerospace, and Volocopter, requesting the FAA revise, remove,
or clarify proposed airworthiness criteria related to bird strike
requirements for the Model M001.
Some commenters requested that the FAA increase the bird-impact
size, while other commenters requested that the bird mass should not be
prescribed, or a lower bird mass should be used with considerations for
multiple bird strikes. Some commenters requested complete removal of
the requirement, while other commenters only requested removal of the
requirement for bird deterrence devices. Several commenters questioned
the bird mass differences between the aircraft level requirement in
proposed AM1.2320, the propeller requirement in Sec. 35.36, and the
bird ingestion evaluation in AM1.2718. One commenter requested the FAA
align bird strike requirements with those in EASA SC-VTOL.
The FAA maintains the rationale presented in the notice of proposed
airworthiness criteria for the proposed level of bird strike protection
for the Model M001. The proposed requirements were based on the
increased exposure to birds in the environment in which the Model M001
is expected to operate, the expectation of public safety, and the
recommendations presented in the
[[Page 45954]]
Aviation Rulemaking Advisory Committee (ARAC) Rotorcraft Bird Strike
Working Group (RBSWG) report.\3\
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\3\ ARAC RBSWG Report, Rev. B, May 8, 2019, page 15, Section
``Bird Mass'' (ARAC RBSWG Report), https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/ARAC%20RBSWG%20Final%20Report%20Rev.%20B.pdf.
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The safety level obtained with the 2.2-lb bird strike requirement
for transport category rotorcraft (as established in Sec. 29.631) has
been demonstrated in service to be sufficient. Similarly, the existing
bird strike requirement with a 4.0-lb bird for type certificated
propellers (established in Sec. 35.36) has also been demonstrated in
service to be sufficient. The bird ingestion requirements in AM1.2718
are not driven by either of these bird sizes. Therefore, the proposed
bird impact protection requirement remains unchanged and will retain
the proposed 2.2-lbs at the aircraft level, while maintaining propeller
requirements at 4.0-lbs in Sec. 35.36.
The FAA also considered the comments received on the bird deterrent
system requirement in proposed AM1.2320(b), and the FAA concurs with
not adopting this proposal. Although the FAA is aware of some research
supporting the use of such devices, the FAA agrees the data is
insufficient to mandate such a system at this time. The FAA encourages
applicants such as Archer to consider voluntary implementation of these
systems or similar bird deterrence mitigations, as good design
practice.
The FAA also received comments that questioned whether the bird
strike requirement should be listed under proposed AM1.2320, ``Occupant
Physical Environment,'' since as written, it applies to more than just
the occupant physical environment. The FAA agrees with these comments.
The bird strike requirement placed in proposed AM1.2320 was intended
and described in the notice as an aircraft-level requirement.
Therefore, the FAA did not adopt proposed AM1.2320(b) and instead
placed some of the requirements from proposed AM1.2320(b) into a new
AM1.2311, ``Bird Strike'' in Subpart D, ``Design and Construction,'' to
reinforce its intent as a general, aircraft-level requirement. Lastly,
several commenters expressed concern with flocking bird strikes that
could affect multiple engines at the same time and recommended this be
addressed by the ingestion requirements in AM1.2718(a). The FAA notes
that the airworthiness criteria in Subpart H apply to each single
engine used in the aircraft distributed propulsion system. The
requirements in AM1.2718(a) address ingestion from likely sources such
as foreign objects, birds, ice, and hail, and are intended to capture
engine effects from any ingestion source determined to be applicable to
the Archer electric engine design. Common cause effects across multiple
engines will be addressed under the applicable aircraft-level
requirements, including Sec. 23.2510, so no change to the engine
airworthiness criteria is necessary.
Fire and High Energy Protection
The FAA received and reviewed comments from Airbus, EASA, GAMA,
JCAB, Lilium, Odys, Overair, TCCA, and Volocopter requesting that the
FAA revise, remove, or clarify proposed airworthiness criteria related
to fire and high energy protection on the Model M001.
Several commenters recommended the FAA revise Sec. Sec. 23.2325
and 23.2270 to protect against fires in baggage and cargo compartments
propagating and creating an unsafe condition. The commenters suggested
incorporating requirements similar to those in EASA SC-VTOL.2270, and
further recommended clarifying proposed Sec. 23.2325 by removing the
references to part 23 airplane certification levels.
The FAA agrees with the need to mitigate the risk of fires in
baggage and cargo compartments, commensurate with the intended level of
safety for the Model M001. The FAA reviewed the baggage and cargo
compartment fire protection requirements in parts 23 and 27, the
intended operational uses of the Model M001, and the EASA SC-VTOL
requirements. The proposed airworthiness criteria did not require the
design to alert the pilot of a fire in a baggage or cargo compartment,
or require these compartments be constructed of or lined with fire
resistant materials to protect the aircraft and occupants if the pilot
was unaware of a baggage or cargo compartment fire. However, part 27
contains requirements to protect rotorcraft occupants from the risk of
fire in a baggage compartment through the use of flame and fire
resistant materials in its construction. The FAA revised proposed Sec.
23.2325 (now AM1.2325) by removing the part 23 airplane certification
levels. The FAA also added AM1.2325(e) requiring that the Model M001
baggage and cargo compartments be constructed of or lined with fire
resistant materials, similar to Sec. 27.855(a)(2), or be equipped with
a fire or smoke detection system to allow the pilot to take immediate
action to land, or be located where a fire would be visible to the
pilots and accessible for the manual extinguishing of a fire, which
adopts some elements of SC-VTOL.2270.
A commenter recommended the FAA revise proposed Sec. 23.2325 to be
more generic by specifying performance-based safety objectives. The FAA
does not agree, as the revisions to proposed Sec. 23.2325 (now
AM1.2325) discussed previously are specific to the Model M001.
The FAA received comments recommending retaining the language in
Sec. 23.2330 of ``designated fire zone'' in lieu of the proposed
AM1.2330 ``fire zone.'' The term ``fire zone'' includes designated fire
zones and new fire zones developed to address fire threats from new
technologies. Much of existing guidance is defined for designated fire
zones, which assume a fire involving kerosene or aviation gasoline.
Other terms will be determined by the applicant, including designated
fire zones, to distinguish between different types of fire zones and
the fire threat that exists in those zones. The difference in language
does not impose requirements beyond the intent of part 23, and also
allows new fire zones to be established for aircraft using non-
conventional propulsion and energy supply. No changes were made as a
result of these comments.
The FAA received a comment to align the language in AM1.2330(a) and
AM1.2330(b) (``fire zone'') with the language in SC-VTOL.2330
(``designated fire zone''). As discussed above, the FAA has moved away
from using the term ``designated fire zone.'' EASA SC-VTOL.2330(a) is
broader than AM1.2330(a) and includes additional components by applying
to ``flight critical systems'' instead of only ``flight controls.''
Although AM1.2330 is not as broad as EASA SC-VTOL.2330(a) as far as the
scope of components, it is broader with respect to the types of fire
zones that those components must address, by using the term ``fire
zone'' instead of ``designated fire zone.'' Protection of flight
critical systems other than flight controls and ensuring CSFL after a
fire or release of stored energy are addressed in AM1.2440 and Sec.
23.2510.
The FAA received multiple comments to add survivable emergency
landing fire protection requirements to Sec. 23.2325. The FAA notes
that such conditions are already covered by AM1.2430(a)(6), which
states that each energy system must be ``. . . designed to retain
energy under all likely operating conditions and to minimize hazards to
occupants and first responders following an emergency landing or
otherwise survivable impact (crash landing).'' No changes are necessary
as a result of these comments.
[[Page 45955]]
The FAA received a comment to add a requirement to AM1.2335 to
minimize the risk of electrical shock to the crew, passengers, and
service and maintenance personnel, similar to the requirement in Sec.
27.610(d)(2). This concern is adequately addressed by proposed
AM1.2335(b), which requires the appropriate protection against
hazardous effects caused by accumulation of electrostatic charge. No
changes were made as a result of this comment.
The FAA also received a comment to revise AM1.2335(b) to require
protection against catastrophic and hazardous effects. The proposed
airworthiness criteria state that the aircraft must be protected from
hazardous effects, which represent the minimum hazard level that must
be addressed; by definition, this requires that catastrophic effects
must also be addressed. No changes are necessary as a result of this
comment.
The FAA received comments questioning proposed AM1.2440 in lieu of
requiring compliance with Sec. 23.2440 for powerplant fire protection.
AM1.2440 is more performance-based, allowing for all powerplant related
fire protection concerns to be covered by a singular airworthiness
criteria. No changes are necessary as a result of this comment. The FAA
received comments recommending replacing the term ``powerplant system''
in AM1.2440 with ``powerplant'' or ``powerplant installation.'' The FAA
does not concur as the proposed terminology is consistent with Sec.
23.2410. No changes were made as a result of these comments.
Propulsion Safety and Integration
The FAA received comments from Airbus, ASD-Europe, EASA, GAMA,
Leonardo, Lilium, Odys, Overair, TCCA, Rolls-Royce, and Volocopter
requesting that the FAA revise, remove, or clarify the proposed
airworthiness criteria related to propulsion safety and integration on
the Model M001.
Proposed AM1.2405(d) specifies ``extremely remote'' as an
acceptable probability of failure for power or thrust control systems,
assuming manual backup capability. Several commenters stated that
reliance on manual backup control of power or thrust on distributed
propulsion powered-lift is unlikely to be acceptably achievable to
ensure CSFL, and that failure of the propulsion control system is
potentially catastrophic. Commenters also stated that specifying the
power or thrust control system failure probability as extremely remote
may be inconsistent with the extremely improbable requirement in
AM1.2135.
The FAA agrees the airworthiness criteria should not specify an
acceptable failure probability for power or thrust controls systems on
a distributed propulsion powered-lift. Additionally, the FAA agrees
that control of distributed propulsion powered-lift, using manual
control of individual engines and propellers, should not be assumed.
The FAA revised AM1.2405 by not adopting proposed paragraph (d). The
appropriate hazard classification and failure probability for power or
thrust control systems will be determined using the aircraft-level
system safety process in Sec. 23.2510, as well as AM1.2135, if
controllability is affected.
The FAA received a comment that AM1.2405(b) and Sec. 23.2410(a)
contradict one another, with the suggestion to remove the phrase ``if
continued safe flight and landing cannot be ensured, the hazard has
been minimized'' from Sec. 23.2410(a). The FAA disagrees. AM1.2405
establishes the safety objective for power or thrust control systems,
whereas Sec. 23.2410 is applicable to all powerplant systems and
permits minimization of the hazard in limited cases. No changes were
made as a result of this comment.
Multiple commenters recommended the FAA replace proposed AM1.2405
(power or thrust control systems) and AM1.2425 (powerplant operational
characteristics) with a requirement to comply with Sec. Sec. 23.2405
(automatic power or thrust control systems) and 23.2420 (reversing
systems), or otherwise address those systems under the safety analysis
requirements of Sec. 23.2510. Commenters also recommended the
airworthiness criteria be revised to allow the propulsion-control
system to be evaluated along with the flight control system within the
aircraft-level safety analyses required by Sec. 23.2510. The FAA does
not agree with these recommendations and notes that Sec. Sec. 23.2405
and 23.2420 are not limited to functions defined in former Sec. Sec.
23.904 and 23.933, as discussed in the preamble to part 23 amendment
23-64.\4\ As noted previously, the FAA agrees that for the Model M001,
the engines and propellers should be considered part of the flight
control system, to include at a minimum all equipment and systems used
for control of pitch, roll, yaw, and vertical motion. Furthermore, the
subsystem analysis required by AM1.2405 for the engine power or thrust
control system does not relieve the applicant from aircraft-level
requirements such as AM1.2300, Sec. 23.2500, or Sec. 23.2510 when
incorporated into a system such as the flight control system.
Conversely, specific subsystem requirements, such as AM1.2405, are not
imposed on other subsystems that make up a higher-level system simply
because they become part of a higher-level system. The FAA did not
change the proposed criteria as a result of these comments; however, as
noted previously, references to the ``reverser system'' in proposed
AM1.2405 have not been adopted because that system is not applicable to
the Model M001.
---------------------------------------------------------------------------
\4\ 81 FR 96639 (Dec. 30, 2016).
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Multiple commenters requested the FAA consider modifying
AM1.2425(b), ``Powerplant Operational Characteristics,'' to include
wording from SC-VTOL.2425(b) that would only require inflight engine
shutdown and restart capability if the safety benefits outweigh the
hazards. Another commenter requested clarity on AM1.2425, which
requires a means for shutdown and restart of the powerplant within an
established operational envelope. It does not prohibit procedures or
control logic that would restrict engine restart under certain
conditions. The FAA disagrees with modifying the criteria. The FAA will
address the requirements of appropriate shutdown and restart procedures
through the aircraft flight manual limitations and operating
procedures. No changes were made as a result of these comments.
One commenter suggested the FAA change AM1.2430(a)(1) to include
``control and management systems'' along with energy storage and supply
systems. The FAA agrees that battery control and management systems are
covered by AM1.2430(a)(1) in addition to Sec. 23.2525, but does not
consider a change necessary as the FAA considers the term ``energy
storage and supply systems'' to include battery control and management
systems. The FAA received another comment requesting to remove Sec.
23.2525(b) as it was duplicative to AM1.2340(a)(1). The FAA does not
agree with this request and made no changes from the comment as Sec.
23.2525 addresses required power for intended operations for all
aircraft systems that use the electrical storage system, whereas
AM1.2430(a)(1) contains propulsion criteria that ensures the
independence between multiple electrical storage systems providing
electrical power to the propulsion system.
[[Page 45956]]
Commenters requested the FAA clarify ``where the exposure to
lightning is likely'' in AM1.2430(a)(2), which they believe could be
interpreted in different ways. One interpretation suggested by
commenters is to consider ``likely'' as it applies to areas of the
aircraft where lightning may strike, while another interpretation is in
reference to operating environments where lightning is likely. The FAA
agrees with this concern and has revised the airworthiness criteria by
removing the phrase ``where the exposure to lightning is likely.'' The
FAA notes that AM1.2430(a)(2) and Sec. 35.38 assume the aircraft will
be exposed to lightning regardless of any environmental operating
limitations and require protection of the energy system from
catastrophic events. The applicant will show compliance with
AM1.2430(a)(2) for the Model M001 consistent with other type
certificated products by identifying areas of the powered-lift where
direct attachment of lightning is ``likely,'' and evaluating the
resulting effects.
The FAA received a comment asking the FAA to consider the failure
due to overload of the landing system in AM1.2430(a)(6). The Model M001
is not required to address specific failures due to overload of the
landing system since its landing system is not located near its energy
storage systems. No changes were made as a result of the comment.
The FAA received a comment requesting that airworthiness criteria
be added to protect occupants from possible hazards from the energy
systems. The FAA notes that proposed AM1.2430(a)(6), as written, covers
this and therefore did not make changes as a result of this comment.
The FAA also received a comment recommending that AM1.2430(a)(6) be
expanded to include minimizing hazards to emergency service responders
in addition to occupants. The FAA concurs with this suggestion and adds
first responders to the airworthiness criteria.
Commenters requested the FAA explain the reservation of proposed
AM1.2430(a)(7) and AM1.2430(c)(2). A commenter also recommended the FAA
adopt EASA SC-VTOL.2430(a)(7) and add it as AM1.2430(a)(7) to ensure
appropriate power quality within the energy system. The FAA did not
incorporate the requirements from 23.2430(a)(7), which are similar to
the requirements from EASA SC-VTOL.2430(a)(7), or (c)(2) into the Model
M001 proposed criteria, and instead listed them as ``Reserved,''
because they cover physical contamination of stored energy. Stored
electrical energy is not susceptible to physical contamination in the
way that convention fuel is. Damaged or failed electrical storage and
distribution systems may prevent delivery of stored electrical energy
to an intended load, which is a different condition than contaminated
energy. The FAA notes these concerns are covered by uninterrupted
energy supply and fluctuation requirements under AM1.2430(a)(4). To
avoid confusion, the FAA did not adopt the proposal to ``reserve''
paragraphs AM1.2430(a)(7) and (c)(2) and renumbered (c)(3) accordingly.
The FAA received a comment that likely hazards for energy systems
are not limited to temperature influences as mentioned in
AM1.2430(b)(2). The FAA agrees and did not adopt the qualifier ``due to
unintended temperature influences'' in these final airworthiness
criteria.
Several commenters suggested clarification on the application of
system safety requirements, propulsion requirements, and flight control
system requirements due to the integration of these functions on the
aircraft. The commenters questioned whether power or thrust control
system requirements need to be applied to flight control systems or if
flight control system requirements need to be applied to power or
thrust control systems. The FAA concurs with the commenters' request to
consider the engines and propellers as part of the flight control
system. The flight control system includes, at a minimum, all equipment
and systems used for control of pitch, roll, yaw, and vertical motion.
The FAA notes that the subsystem analysis required by AM1.2405 for the
engine power or thrust control system does not relieve the applicant
from higher-level requirements such as those in AM1.2300, Sec.
23.2500, or Sec. 23.2510, when engine or thrust control systems are
incorporated into a higher-level system such as the flight control
system. Conversely, specific subsystem requirements such as AM1.2405
would not be imposed on other subsystems that make up a higher-level
system simply because they become part of that higher-level system. The
safety requirements in Sec. 23.2510 apply at the aircraft level to the
integrated functions of all systems on the aircraft, in addition to
specific system requirements such as AM1.2300 and AM1.2405.
Several commenters expressed concern regarding the appropriateness
of the system-level safety objectives in proposed AM1.2405 and Sec.
23.2425 for such highly integrated systems. The commenters suggested
AM1.2405 and AM1.2425 are not necessary, since compliance with Sec.
23.2510 can require the applicant to define both system and aircraft
level safety objectives.
The FAA recognizes there may be inconsistencies between safety
objectives required at the powerplant installation level and those at
the aircraft level, but notes this is the case for type certificated
airplanes and rotorcraft. Existing powerplant rules define a minimum
level of safety that permits certification of a broad range of products
for single and multi-engine aircraft. One common requirement for
powerplant installations has been the ``no single failure'' concept,
which is practically applied given the number of engines installed.
This concept remains critical even for highly integrated and
distributed powerplant systems. Aircraft level safety objectives may
not drive the level of safety typically provided in a powerplant
installation, such as isolation between all engines on a multi-engine
aircraft with more than two engines, so the powerplant requirements
establish a minimum safety objective that may not always align with
those at the aircraft level. As powered-lift and distributed propulsion
systems evolve, there may be less need to capture powerplant
installation unique safety requirements. Until then, the FAA will use
AM1.2405 to capture those requirements for the Model M001 and ensure
the powerplant installation level of safety is appropriate regardless
of the aircraft level safety objectives.
Multiple commenters requested clarification regarding the
definition of ``energy'' and the instances in the criteria where liquid
fuel is still relevant, despite the consideration of electric
propulsion systems. The term ``fuel'' is used in part 23 and includes
any form of energy used by an engine or powerplant installation such as
provided by carbon-based fuels or electrical potential.\5\ The FAA
recognizes that using the term ``fuel'' instead of ``energy'' has
implied the criteria are limited to non-fossil-fuel-based propulsion
systems and is inconsistent with language used by other airworthiness
authorities. As such, the FAA has replaced the term ``fuel'' with
``energy'' throughout these Model M001 airworthiness criteria. The FAA
notes that ``energy'' includes any form of energy, including carbon-
based fuels, electrical potential, and other means of energy storage or
power generation for propulsion.
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\5\ 81 FR 96641 (Dec. 30, 2016).
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Several commenters requested that the FAA revise proposed
AM1.2400(b) to clarify that the Model M001 engines
[[Page 45957]]
and propellers will not be individually issued type certificates, but
rather approved under the aircraft's type certificate, and as such, any
requirements mentioning the ``type certificate'' should be excluded.
The FAA agrees and has revised AM1.2400(b) to remove the requirement
that each engine and propeller installed on the Model M001 have a type
certificate.
The FAA received a comment to distinguish between airplane and
engine hazards in AM1.2000(e). The requirement in AM1.2400(e) addresses
powerplant components at the aircraft level. Engines are one of many
powerplant components installed at the aircraft level, each of which
must meet any limitations or installation instruction provided with
that component or be shown to not to create a hazard. Engine specific
hazards for the Model M001 are found in subpart H of the airworthiness
criteria. The FAA disagrees that the distinction requested by the
commenter is necessary, and no changes were made as a result of this
comment.
The FAA received comments requesting the FAA either remove Sec.
23.2525(c) and modify AM1.2430(a)(3) to explicitly include energy
storage systems, or revise Sec. 23.2525(c) to remove the primary
source failure consideration. The FAA disagrees. Section 23.2525
addresses required power considering the failures and malfunctions of
the primary source at the aircraft level, whereas the requirements in
AM1.2430(a)(3) are specific to energy systems used for propulsion. No
changes were made as a result of these comments.
System Safety
The FAA received and reviewed comments from ASD-Europe, Airbus,
ALPA, EASA, Leonardo, Lilium, Odys, Vertical Aerospace, Rolls-Royce,
TCCA, Volocopter, an individual commenter, and an anonymous commenter,
requesting the FAA revise, remove, or clarify proposed airworthiness
criteria related to system safety and cybersecurity requirements for
the Model M001.
Several commenters cited differences between EASA's SC-VTOL and the
proposed FAA airworthiness criteria for the Model M001 with regard to
EASA's creation of a ``Category Enhanced'' set of requirements. EASA
included a structural requirement in SC-VTOL.2250, ``Design and
construction principles,'' that for Category Enhanced a single failure
must not have a catastrophic effect upon the aircraft. The FAA
acknowledges that the airworthiness criteria for the Model M001 as a
special class aircraft differ from the requirements in EASA's SC-VTOL,
which is a set of generalized requirements intended to cover a class of
aircraft. The FAA's long-standing technical practice manages risk due
to structural failures through the use of critical or life-limited
parts, which mitigates any need to address potential catastrophic
structural failure modes under the system safety requirements of Sec.
23.2510. While this practice differs from that of EASA's approach, the
FAA finds both approaches comparable and acceptable for risk
mitigation. As discussed previously, the FAA revised proposed Sec.
23.2250(c) (now AM1.2250(c)) to add a requirement that single failures
must not result in a catastrophic effect upon the aircraft.
Several commenters identified that these criteria do not include
specific failure condition probability targets or required development
assurance level criteria and requested that they be included with
appropriate rationale. The FAA does not agree, as existing aircraft
airworthiness standards (parts 23, 25, 27, and 29) also do not
prescribe specific failure condition probability targets or development
assurance level criteria. This guidance may be found in advisory
circulars or industry consensus standards, which provide one means, but
not the only means, for showing compliance with the regulatory
requirements. These means will likely need to be modified to consider
powered-lift designs such as the Model M001.
One commenter recommended the FAA revise the proposed requirement
to comply with Sec. 23.2510 to include a clarification on the
applicability of the standard, as it pertains to systems and equipment
installed in the aircraft and how it relates to other requirements
contained in other sections of the airworthiness standards. The FAA
disagrees. The FAA proposed that the Model M001 comply with Sec.
23.2510 without modification because the FAA intentionally developed
that rule as a regulation of general requirements that do not supersede
any requirements contained in other part 23 sections. The FAA intends
the same application for the Model M001.
Several commenters expressed concern over the absence of a ``no
single failure'' catastrophic failure condition criteria in these
airworthiness criteria, citing its inclusion in EASA SC-
VTOL.2510(a)(1). The FAA does not agree that a specific requirement
prohibiting catastrophic single failures is necessary in the
airworthiness criteria. Existing parts 23, 25, 27, and 29 airworthiness
standards do not contain a ``no single failure'' requirement for
catastrophic failure conditions, and the FAA considers these
longstanding existing airworthiness standards acceptable. Although
preventing ``single failures'' is addressed in FAA guidance material
(e.g., Advisory Circulars 25.1309-1A and Advisory Circular 27-1B), it
is one means, but not the only means, for showing compliance with the
regulatory requirements. The FAA intends the same application for the
Model M001.
Several commenters recommended the FAA clarify requirements for
addressing cybersecurity. The FAA acknowledges that these aircraft
involve many new technologies which are highly integrated, and any
cybersecurity vulnerabilities must be appropriately assessed and
addressed. The FAA is addressing cybersecurity through AM1.1529 and
Sec. 23.2500, Sec. 23.2505, and Sec. 23.2510. No changes were made
as a result of these comments.
Lightning Protection
The FAA received and reviewed comments from EASA, GAMA, Lilium,
Overair, and TCCA requesting the FAA revise, remove, or clarify
proposed airworthiness criteria intended to address hazards that may
result from a lightning attachment on the Model M001. These
requirements include consideration for lightning common cause effects
due to the potential for simultaneously affecting multiple systems. The
proposed airworthiness criteria considered inadvertent exposure to
lightning producing environments, including flight into clouds, as well
as cold or icy weather conditions. The FAA determined that the highly
integrated systems of the Model M001 aircraft require lightning
protection.
One commenter requested the FAA clarify why the lightning indirect
effects requirements are not applicable to systems with major failure
conditions. The FAA notes that the lightning requirements are intended
to be applicable to systems with major failure conditions for aircraft
approved for IFR operations. For aircraft approved for IFR operations,
proposed AM1.2515(b) is applicable to systems with hazardous or major
failure conditions, similar to Sec. 27.1316(b).
Multiple commenters recommended the FAA revert proposed AM1.2515 to
Sec. 23.2515 to limit the applicability of lightning requirements to
aircraft approved for IFR operations that cannot show exposure to
lightning is unlikely. The Model M001 incorporates systems that are
critical in VFR and IFR operations that require protection
[[Page 45958]]
against indirect effects of a lightning strike. A lightning attachment
may occur during flight, when operating through or in the vicinity of
lightning producing environments. Aircraft operating in instrument
meteorological conditions (IMC) may encounter lightning, and aircraft
operating in day or night visual meteorological conditions may
inadvertently encounter lightning producing environments such as flight
into clouds and freezing or icy weather conditions. Systems that
perform functions essential to CSFL must demonstrate immunity to
lightning for all operations to achieve the intended safety objectives
for catastrophic failure conditions. The FAA finds the requirements in
AM1.2515 to be appropriate for the systems on the Model M001 and made
no changes as a result of these comments.
The FAA received a comment asking for clarification of
AM1.2515(a)(2) stating that it could be incorrectly interpreted as the
system could be allowed to fail when exposed to lightning without
recovery after exposure. The FAA does not agree that AM1.2515(a)(2) may
be misinterpreted. Demonstration of lightning immunity is required for
systems with catastrophic failure conditions. The exception for
recovery conflicts in AM1.2515(a)(2) is based on aircraft operational
or functional requirements independent of lightning exposure. The
expectation is that a system recovers normal operation of a function
without impact to safety of flight by design. No changes were made as a
result of this comment.
Multiple commenters recommended the FAA consider whether systems
with hazardous and major failure conditions meet lightning requirements
for aircraft not approved for IFR operations. The FAA notes that
aircraft not approved for IFR operations are restricted from flight
into IMC and must use outside visual references. An aircraft operating
in IMC may encounter lightning producing environments, a hazard which
requires more stringent requirements than aircraft certified
exclusively for VFR operations. Limiting AM1.2515(b) to IFR operations
therefore maintains the level of safety intended for protection against
lightning threats. Section AM1.2515(b) is applicable to IFR operations
and systems with hazardous (level B) or major (level C) failure
conditions. Section AM1.2515(a) is applicable to all operations and
systems with catastrophic failure conditions. This approach achieves
the intended safety objectives.
Commenters recommended deleting the word ``significantly'' from the
text of AM1.2515(b) so that the requirement is clearly identified as
applicable to electrical and electronic systems with hazardous and
major failure conditions. The FAA concurs since AM1.2515(b) is
applicable to IFR operations and systems with hazardous or major
failure conditions. The FAA did not adopt the term ``significantly''
from proposed AM1.2515(b) to ensure both major and hazardous failure
conditions are appropriately assessed.
HIRF
The FAA received and reviewed comments from EASA, Overair, and TCCA
requesting the FAA revise, remove, and clarify proposed airworthiness
criteria related to HIRF exposure.
Commenters requested consideration for HIRF common cause effects
due to the potential of affecting multiple systems simultaneously,
since radio frequency transmitters are continuously evolving, and
future spectrum expansions are anticipated. The FAA agrees that the
HIRF environment and sources are unpredictable and that the aircraft
and highly integrated systems require robust HIRF protection, but
considers the proposed requirements adequate to address this concern.
One commenter requested the FAA clarify why operation under IFR is
considered to relax the HIRF requirements, but not the lightning
criteria. Another commenter requested the FAA clarify why the HIRF
requirements are not applicable to systems with major failure
conditions. Several commenters also requested the FAA remove the
limitation that Sec. 23.2520(b) be only applicable for aircraft
approved for IFR operations, similar to SC-VTOL.2520(b).
The FAA notes that proposed AM1.2515 and AM1.2420 provide
consistent requirements for the protection of electrical and electronic
systems from the effects of lightning and HIRF, respectively. The FAA
does not concur that the HIRF requirements are relaxed for IFR. The FAA
changed the proposed requirement to comply with Sec. 23.2520(a) and
(b) to new AM1.2520, to remove the qualifier ``significantly'' from
Sec. 23.2520(b). AM1.2520(a) is applicable for all operations and
systems with catastrophic failure conditions, aligned with AM1.2515(a).
Limiting AM1.2520(b) to IFR operations maintains an acceptable level of
safety, as AM1.2520(b) is intended to be applicable to systems with
hazardous or major failure conditions. This also aligns with similar
requirements in AM1.2515(b) for lightning. The FAA did not adopt the
term ``significantly'' from proposed AM1.2420(b), similar to
AM1.2515(b), to ensure that major and hazardous failure conditions are
appropriately assessed for HIRF as well as for lightning. This approach
achieves the intended safety objectives and aligns the airworthiness
criteria with the appropriate level of safety intended by utilizing
appropriate standards from both parts 23 and 27, revised to be
appropriate for the Model M001.
Flightcrew Interface
The FAA received and reviewed comments from ALPA, ANAC, EASA, GAMA,
Lilium, Odys, Overair, TCCA, and an anonymous commenter requesting the
FAA revise, remove, or clarify proposed airworthiness criteria related
to flightcrew interface requirements on the Model M001.
The FAA received comments requesting that the FAA replace the
language in AM1.2600(a) and (b) with the language in Sec. 23.2600(a)
and (b). The Model M001 is capable of using one or more sources of lift
to perform a particular phase of flight. Therefore, using the unchanged
wording from Sec. 23.2600(a) is not sufficient and does not include
hover. AM1.2000 incudes definitions for ``sources of lift'' and
``phases of flight,'' and those defined terms were used in proposed
AM1.2600(a). The FAA included ``without excessive concentration, skill,
alertness, or fatigue'' in proposed AM1.2600(b) to address the human
factors elements used to control the aircraft. The Model M001 includes
increased levels of automation and technology that may impact pilot
concentration, alertness, and fatigue, so the inclusion of ``without
excessive concentration, skill, alertness, or fatigue'' language is
necessary. No changes were made as a result of these comments.
The FAA also received a comment requesting clarification between
human factor differences in AM1.2135(a) and AM1.2600(a). The same
commenter suggested revising AM1.2160(a). AM1.2135(a) describes human
factors requirements as they relate to controllability of the aircraft
while AM1.2160(a) focuses on the human factors in the context of the
flightcrew interface. No changes were made as a result of these
comments.
The FAA received a comment to restructure the header paragraph of
AM1.2620 such that the manufacturer must present pertinent information
for the aircraft for all possible configurations of thrust or flight.
The FAA disagrees as the requirement is applicable to the overall
aircraft and must contain information concerning
[[Page 45959]]
aircraft configurations as necessary for defining the required
information in AM1.2620. No change is necessary as a result of this
comment.
One commenter requested clarification on procedures for the
flightcrew following an abnormal battery anomaly. The FAA notes that
AM1.2620(a)(5) addresses this concern by requiring information
necessary for safe operation because of design, operating, or handling
characteristics to be specified in the Airplane Flight Manual, which
provides procedural guidance for flightcrew. Procedures following an
abnormal battery anomaly are necessary for safe operation. No changes
were made as a result of this comment.
One commenter requested that the FAA include AM1.2620(a)(5) as
information that must be approved by the FAA. The FAA disagrees, as
this requirement is consistent with the existing airworthiness
standards for normal category aircraft. No changes were made as a
result of this comment.
One commenter requested clarification on whether the requirements
in proposed AM1.1529 (ICA) and AM1.2615 (flight, navigation, and
powerplant instruments) would also address EASA SC-VTOL.2445, Lift/
thrust system installation information. Although the Model M001
airworthiness criteria do not contain a requirement that directly
aligns with EASA's SC-VTOL.2445, the commenter is correct that AM1.1529
and AM1.2615 address the lift/thrust installation requirements in EASA
SC VTOL.2445. In addition, the lift/thrust installation requirements in
EASA SC-VTOL.2445 would be addressed for the Model M001 by the
requirements in Sec. Sec. 23.2605 and 23.2610. The FAA received
multiple comments to modify Sec. 23.2605 to add a requirement that
information related to safety equipment must be easily identifiable and
its method of operation must be clearly marked, as specified in SC-
VTOL.2605(d). The language requested by the commenters is already
required by Sec. 23.2535 and therefore no changes are necessary as a
result of these comments.
One commenter requested the FAA revise proposed AM1.2615(b)(2) to
delete criteria for single failure and probability. The FAA does not
agree and notes that this requirement is essential for CSFL after
probable failures, both singular and in combination.
Electric Engines
The FAA received and reviewed comments from Airbus, ANAC, EASA,
GAMA, JCAB, Lilium, Odys, Overair, Rolls-Royce, TCCA, Vertical
Aerospace, and Volocopter requesting the FAA revise, remove, or clarify
proposed airworthiness criteria related to electric engines for the
Model M001.
One commenter recommended replacing the phrase ``intended aircraft
application'' throughout subpart H with language specific to the Model
M001 design. Another commenter recommended replacing ``declared
environmental limits'' with ``aircraft environmental and operating
limitations'' throughout subpart H. The FAA does not agree that more
specific language is necessary, as ``intended aircraft application''
and ``declared environmental limits'' are sufficient to meet the
electric engine certification requirements. No changes were made as a
result of these comments.
The FAA received comments recommending the removal of Sec.
33.5(a), (b), and (c) and Sec. 33.29 from the engine requirements in
Subpart H. One commenter stated these requirements should not be
imposed for an engine that is not being type certificated as an
independent product, as is the case for the Model M001. This commenter
also stated the engines for the Model M001 are being certified under
the umbrella of the aircraft type certificate; as a result, the
installation and operating instructions will already be part of the
type design data package at the aircraft level. Other commenters stated
that no additional burden from individual ``engine-only'' requirements
for data sheet content is necessary, from Sec. 33.5(a), (b), and (c),
AM1.2702, AM1.2706, AM1.2710(j)(2), AM1.2718(c) and (d), AM1.2719(b)
and (e), and AM1.2733(d)(2). The FAA recognizes the engines will be
approved with the Model M001 aircraft, but instructions for installing
and operating the engines are required, as well as other engine
airframe interfaces such as instruments, connections, sensors, etc.,
whether the engines are approved with the aircraft or certificated
under their own type certificate. The FAA made no changes in response
to these recommendations.
The FAA received comments on the applicability of subsystems
equipment installed in an electric hybrid propulsion system (EHPS), as
referenced in EASA Special Condition E-19 EHPS.330. The FAA
acknowledges these comments but notes that they are not applicable to
the Model M001, since the Archer engine architecture does not include
the electric hybrid propulsions systems associated with E-19 EHPS.330.
One commenter questioned whether the requirements of EASA Special
Condition E-19 EHPS.80, which accounts for the complete inability to
isolate components that could cause a hazard to aircraft, should be
added to the airworthiness criteria for the Model M001. The FAA does
not agree, as the requirement to isolate components that could cause a
hazard to the aircraft is in EHPS.350(d), EHPS Control System, not in
EHPS.80. The requirement in EHPS.350 raised by the commenter is
addressed by AM1.2710 Engine Control Systems, AM1.2717 Safety Analysis,
and AM1.2733 Engine Electrical Systems. Since the Archer M001 is a
special class aircraft and the engines will be approved with the
aircraft, the means by which components prevent a hazard from
developing may be implemented either at the engine-level or at the
aircraft-level. No changes were made as a result of these comments.
Another commenter noted the proposed requirement to comply with
Sec. 33.75(e)(1) includes a reference to Sec. 33.4 (ICA), although
the proposed airworthiness criteria do not include a requirement to
comply with Sec. 33.4. The commenter recommended either removing the
reference to Sec. 33.4 or adding a reference to Appendix 1, AAM1.2701,
A33.2, A33.3, and A33.4. The FAA agrees with the comment. The FAA
proposed AM1.2717 to include those safety analysis standards from Sec.
33.75 that could not be required directly for the Model M001 without
modification. Proposed AM1.2717(c) contained requirements for how the
applicant must comply with Sec. 33.75(e). The FAA has modified
proposed AM1.2717(c) to reference the ICA in AM1.1529 for compliance
with Sec. 33.75(e)(1). During the review of this comment, it was
determined that Sec. 33.75(a)(1) should be included in AM1.2717(a) and
the applicability of AM1.2717(b) should be clarified using information
from the existing standard Sec. 33.75(c). The FAA has revised AM1.2717
accordingly.
The FAA received a comment asking for clarification of the term
``duty cycle'' in proposed AM1.2702(b). The FAA also received a comment
to remove the requirement in proposed AM1.2702(b) to list the duty
cycle on the type certificate data sheet. The FAA disagrees. A duty
cycle is intrinsic with engine ratings. Engine ratings are declared to
support aircraft performance objectives, whereas duty cycles are an
electric engine property that limits the usage of the ratings. The duty
cycle, combined with the rating at that duty cycle, establishes the
capability and the limits for engine usage. A commenter also noted that
the takeoff power time limitation is not defined. While traditional
combustion engines adhere to ``takeoff power time limitations,'' the
[[Page 45960]]
operational considerations for electric aircraft engines, such as duty
cycle and rating, are more pertinent due to their distinct propulsion
system characteristics. A duty cycle and rating at each duty cycle must
be declared, which covers this concern. No changes were made as a
result of these comments.
The FAA received a comment to add specific operating limits to
proposed AM1.2702. The FAA also received a comment to add Sec. 33.7(d)
to the airworthiness criteria to address the accuracy of the engine
control system and necessary instrumentation. Section 33.7(d) applies
to engine performance and operating limitations. The FAA did not
propose to require that the Model M001 comply with Sec. 33.7(d),
because Sec. 33.7(d) focuses on engine control system components
(e.g., speed sensors, actuators, feedback mechanisms) that typically
operate using low voltage power and hydraulic systems. Electric
engines, such as those that are part of the Model M001 design, are
controlled differently. In addition, the Model M001 engine electrical
systems are integrated with aircraft systems instruments that are
necessary for control of the engine, which would not be addressed by
Sec. 33.7(d). Instead, for the Model M001, the engine performance and
operating limitations referenced by Sec. 33.7(d) are addressed by the
airworthiness criteria for the engine control system in AM1.2710 and
the engine electrical system in AM1.2733. No changes were made as a
result of these comments.
The FAA also received a comment that proposed AM1.2702 provided a
redundant definition of the engine ratings with that in Sec. 33.8. The
FAA disagrees. These two engine requirements accomplish different
objectives. AM1.2702 establishes the engine's ratings and limits, while
Sec. 33.8 ensures each rating applies to the lowest power that all
engines of the same type may be expected to produce under the
conditions used to determine that rating. No changes were made as a
result of this comment.
A commenter suggested the FAA remove the word ``turbine'' from
Sec. 33.17(a), as it is not applicable to the Archer Model M001. The
FAA notes that proposed AM1.2704, ``Fire Protection,'' was initially
drafted to consider potential arc-fault-initiated fires occurring
anywhere inside or outside the electric engine. However, the commenter
highlighted that the second statement in Sec. 33.17(a) specifically
applies to internal fires in turbine engines and is not relevant to
Archer engines. Consequently, the FAA has modified the airworthiness
criteria to remove the applicability of Sec. 33.17(a) to the Model
M001 and add a new statement to AM1.2704 emphasizing the design and
construction requirements to minimize the occurrence and spread of fire
during normal operation and failure conditions. This modification
results in AM1.2704 having two paragraphs, (a) and (b). This
modification makes a suggestion by another commenter to change the
title of the airworthiness criteria to ``High Voltage Arc Faults and
Fire Protection'' inapplicable.
The FAA received a comment questioning the applicability of Sec.
33.17(b) through (g), which address flammable fluids. The FAA notes
that flammable fluids and flammable fluid storage components could be
used in the Model M001 design. As such, the FAA finds these criteria
applicable and no changes were made. Another commenter suggested that
the requirements of Sec. 33.17 be made more prescriptive, specifically
to require fireproof materials. The FAA notes that this concern is
addressed overall in the Archer design through requirements specified
in AM1.2704, Sec. 33.75(g)(2)(iv), and AM1.2733. Additionally, Sec.
33.17 applies to engine fires resulting from ignition of flammable
fluids. No changes were necessary as a result of this comment.
The FAA received a comment that pass and fail criteria should be
defined for the requirement in proposed AM1.2705 to minimize the
development of an unsafe condition in the engine and recommended using
the criteria in AM1.2717(d)(2). The FAA does not concur. An unsafe
condition is determined by a risk assessment and not solely by the
hazards identified by the hazardous effects in AM1.2717(d)(2). No
changes were made as a result of this comment.
The FAA also received a comment to add ``removal from service'' to
the maintenance actions in proposed AM1.2705. The FAA disagrees. The
statement ``removal from service'' is appropriate to address simple
engine designs that are life limited. However, this statement is not
needed in the Model M001 airworthiness criteria because any maintenance
involving a life limited engine is addressed by AM1.2729(b) and
AM1.2713. No changes were made as a result of this comment.
The FAA received a comment asking why proposed AM1.2720 did not
include ``engine fault conditions.'' The FAA determined it was
necessary to revise AM1.2720(b) to clarify the vibration sources
applicable to this requirement.
The FAA received two comments requesting clarification regarding
whether proposed AM1.2729 (b) allows the applicant the option of not
performing the teardown inspection. The FAA clarifies that the agency
intends AM1.2729(b) to require a teardown inspection except for any
engine parts or components that cannot be torn down. The FAA has
changed proposed AM1.2729(b) to clarify that it only applies to engine
components where a teardown cannot be performed in a non-destructive
manner.
A commenter requested clarification on the difference between the
durability requirements of proposed AM1.2705 and AM1.2726. AM1.2705 is
criteria for durability requirements for design and construction of the
engine, whereas AM1.2726 provides requirements for a durability
demonstration. The FAA modified AM1.2726 to distinguish it from
AM1.2705 by explaining its purpose, which is to establish when the
initial maintenance is required.
A commenter questioned where the requirements in EASA's E-19
EHPS.200 are captured. The FAA notes that Sec. 33.23 establishes the
loads associated with the engine mounting attachments and structure
similar to what would be expected under EHPS.200 for an electric engine
such as in the Model M001. No changes were made as a result of this
comment.
Multiple commenters requested clarification on proposed AM1.2709
concerning failure conditions leading to rotor overspeed. Proposed
AM1.2709 was based on Sec. 33.27 ``Turbine, Compressor, Fan, and
Turbosupercharger Rotor Overspeed.'' The FAA intended the approach used
for establishing the highest possible rotor overspeed in proposed
AM1.2709 to be consistent with the approach in Sec. 33.27(b), except
for the prescriptive overspeed margins. The margins in Sec. 33.27(b)
are based on the physics of what drives the rotors in turbine engines
and turbosupercharger rotors. The mechanisms that can drive electric
engines to an overspeed condition are different from those that govern
combustion engines. No changes were made as a result of these comments.
One commenter recommended that the pertinent characteristics and
capabilities of the Model M001 the applicant must analyze should be
prescriptively included in proposed AM1.2710(g) and AM1.2717(e). The
FAA does not agree that all the pertinent aircraft details that must be
analyzed under AM1.2710(g) and AM1.2717(e) should be prescribed within
the airworthiness criteria as existing aircraft airworthiness standards
[[Page 45961]]
also do not prescribe these pertinent aircraft details. This guidance
may be found in advisory circulars or industry consensus standards,
which provide one means, but not the only means, for showing compliance
with the existing regulatory requirements. These means will likely need
to be modified to consider powered-lift designs such as the Model M001.
During review of the requirements of AM1.2710(j), the FAA also
identified an error in AM1.2710(j)(2), which was originally intended to
cover all engine electrical systems, leading to confusion regarding the
applicability in paragraph (a). The FAA clarifies that the engine
control requirements in AM1.2710 apply to any aspects of the engine
control that interface with aircraft control systems that are necessary
for safe flight and landing. The FAA has corrected this error in the
final criteria by removing the reference to electrical power supplied
to the aircraft by energy regeneration from paragraph (j)(2).
The FAA received a comment to update proposed AM1.2710(e) to
declare the engine control system and the engine electrical
environmental limits, similar to proposed AM1.2823(a)(2). This concern
is already addressed by the airworthiness criteria. Since the engines
are approved with the aircraft, environmental conditions and limits
that were used to substantiate the Model M001 aircraft and its engines
will be used to develop compliance with AM1.2620, ``Aircraft Flight
Manual.'' No changes were made to AM1.2710(e) as a result of this
comment. However, this comment revealed a need to clarify the
requirement in proposed AM1.2727. The purpose of AM1.2727 is to
supplement engine testing with additional component-level and systems-
level tests that expose engine components and systems to operational
conditions that cannot not be achieved in the engine test environment
or with the specified test duration. Also, demonstration shortfalls for
certain electrical properties might occur with other engine tests, such
as the durability demonstration, because the test duration required to
show deterioration in electrical hardware may be impracticable.
One commenter requested the FAA remove proposed AM1.2711(b)(2),
which specifies that the aircraft design is not required to enable the
flight crew to monitor the engine cooling system for a cooling system
failure that would not result in a hazardous engine effect. The FAA
disagrees. Not adopting proposed AM1.2711(b)(2) would result in a
requirement for instrumentation enabling the flightcrew to monitor the
engine cooling system regardless of the hazard level resulting from a
cooling system failure. Although monitoring the engine cooling system
would enable the crew to respond to leading indicators of an overheated
engine and prevent the aircraft from the subsequent effects, the
severity of the effects from an overheated engine, and the appropriate
engine-level protection and mitigation standards, are addressed by the
engine safety analysis. No changes were made as a result of the
comment.
One commenter suggested changing the word ``electromagnetic'' to
``electrical'' in proposed AM1.2712(a). The FAA does not concur with
this change, as electrical system hazards are covered in AM1.2733.
However, the FAA acknowledges that the requirement in proposed
AM1.2712(a) could be clarified and made changes to that effect.
Multiple commenters recommended adding the demonstration to operate
above temperature limits on turbine engines for short-duration ratings
in proposed AM1.2724, and to consider updating proposed AM1.2709 and
AM1.2730 to add the requirements in E-19 EHPS.250(a), ``the failure of
any rotating component or part of an equipment, electric engine or
generator must not lead to the release of high energy debris.'' The FAA
has revised AM1.2724 to remove its applicability to all engine ratings
and also revised the introductory text of AM1.2730 to be more aligned
with part 33 subpart B. The FAA did not find the recommended language
appropriate for AM1.2709 and did not make any changes to AM1.2709.
The FAA received a comment asking for clarification on whether
proposed AM1.2715(c) only applies to engines having torque operating
limitations. AM1.2715(c) applies to an electric engine regardless of
whether the engine is torque limited. Archer can propose ratings and
limits in accordance with AM1.2702 using relevant engine parameters
such as horsepower, torque, rotational speed, and temperature. AM1.2715
and AM1.2725 require tests that range from ground idle and flight idle,
to the rated power or thrust prescribed by these rules. Electric
engines can create torque much faster than combustion engines, and
sudden changes in torque could present a hazard to the aircraft
installation. Therefore, the power response characteristics must
account for the intended aircraft application to ensure the torque
characteristics of the engine and intended aircraft are compatible.
These requirements correspond to Sec. Sec. 33.73 and 33.89
respectively, so the minimum torque or power settings are established
in the procedures that assess the operational capabilities of the
electric engines. The FAA modified proposed AM1.2715(c) to clarify that
this is an engine-level requirement.
One commenter requested the FAA consider EASA's Special Condition
E-19 EHPS.260. The commenter states that proposed AM1.2716 only
addresses hazardous engine effects and applicants should evaluate, as
required by EHPS.260, the effects of any continued rotation on the
system, such as windmilling propellers. The concerns raised by the
commenter are addressed by AM1.2733, ``Engine Electrical Systems.''
AM1.2733(b) (both proposed and final) ensures that the generation and
transmission of electrical power, and electrical load shedding, do not
result in any unacceptable engine operating characteristics or cause
the engine to exceed its operating limits. New AM1.2733 (e)(2) requires
the characteristics of any electrical power supplied from the engine to
the aircraft via energy regeneration to be identified and declared in
the engine installation manual.
The FAA received multiple comments to change the proposed
definition of a minor engine effect in proposed AM1.2717(d)(1). The
commenters recommended using the criteria in Sec. 33.75(g)(1) to
classify the effects of a partial or total loss of engine power in the
Model M001. The Model M001 engine airworthiness criteria do not
classify the engine effect from a complete loss of engine power because
the aircraft level assumptions are different than those used in Sec.
33.75(g)(1). The Model M001 engine airworthiness criteria allow a
complete loss of power in one engine to be classified based on the
effects on the aircraft. No changes were made as a result of these
comments.
Multiple commenters stated that due to the integrated nature of the
Model M001, the system safety analyses required in support of Sec.
23.2510 are adequate and sufficient, and that Sec. 33.75, AM1.2717,
and AM1.2733(f) and (g) should be removed from these airworthiness
criteria. The FAA does not agree with this recommendation, and notes
that Sec. 23.2510 establishes the safety objective for aircraft
systems and equipment ``whose failure or abnormal operation has not
been specifically addressed by another requirement.'' The proposed
subpart H and I requirements include specific engine and propeller
design and testing requirements not covered under aircraft-level
airworthiness criteria and establish a minimum level of safety
equivalent to the existing part 33 and part 35
[[Page 45962]]
airworthiness standards as required under Sec. 21.17(b). Additionally,
these airworthiness criteria prescribe the same requirements for
installed engines and propellers on the Model M001 that would apply to
these engines and propellers if they received separate type
certificates under parts 33 and 35, respectively. The aircraft-level
requirements of Sec. 23.2510 are not sufficient on their own to ensure
engines and propellers will meet the intended level of safety required
by Sec. 21.17(b) for parts 33 and 35. Since the engines will be
approved with the Archer aircraft, these compliance details may be
documented in the appropriate aircraft-level documents with references
to the engine-level requirements in Subpart H.
One commenter recommended removing the prescriptive airworthiness
criteria of subparts H and I and to defer their development to the
means of compliance. Another commenter proposed to use performance-
based aircraft requirements that consign the engines and propellers to
aircraft equipment or systems and relegate engine and propeller
certification requirements to a means of compliance to an aircraft
requirement. The FAA does not agree with these comments and considers
the requirements in subparts H and I to provide an equivalent level of
safety for the Model M001. No changes were made as a result of these
comments.
A commenter requested the FAA reword proposed AM1.2717(d)(1) to
remove an extraneous phrase ``does not prohibit the engine from meeting
its type-design requirements.'' The FAA concurs that the phrase was
unclear and updated AM1.2717(d)(1) for clarity.
A commenter requested clarification regarding why blockage of a
cooling system as described in proposed AM1.2717(d)(2)(ii) is
considered a hazardous engine effect. The FAA notes that the blockage
of a cooling system is not by itself a hazardous engine condition, but
it could contribute to the development of one. Accordingly, the FAA
modified AM1.2717(d)(2)(ii).
A commenter requested the FAA align proposed AM1.2713 with the
safety expectations in EASA's SC-VTOL. The commenter recommended
changing proposed AM1.2713 to specify that no single failure may lead
to a catastrophic event and to exclude the criteria for critical parts.
The FAA does not find the level of safety outlined in SC-VTOL for
``Category Enhanced'' to be applicable to the Model M001 engine failure
classifications, which could be minor, major, or hazardous, but not
catastrophic. The FAA will apply failure classifications that are
consistent with those established in part 33 to provide the equivalent
level of safety required by Sec. 21.17(b). No changes were made as a
result of this comment.
A commenter requested clarification as to whether proposed AM1.2713
would require the same activity for both critical parts and life-
limited parts. An engineering plan, manufacturing plan, and service
management plan will be needed for critical parts and for life-limited
parts as stated in AM1.2713(b).
Commenters requested the FAA clarify what is meant by the
definition of a ``life limited part'' in proposed AM1.2713(a)(2), as it
includes phrases that make it open-ended and indistinguishable from the
definition of a critical part in proposed AM1.2713(a)(1). The FAA
agrees regarding the need for clarification in the definition of life-
limited parts. While retaining the examples in the definition, the FAA
has revised the definition of life-limited part in AM1.2713(a)(2) to be
distinguished by the failure mode related to low-cycle fatigue (LCF)
mechanisms. The revised definition specifies that life-limited parts
may involve rotors or major structural static parts, among other parts
with failure potentially leading to hazardous engine effects due to LCF
mechanisms.
A commenter noted that the FAA made a reference to Sec. 33.70 in
proposed AM1.2713(b) when Sec. 33.70 was not included as a part of the
Model M001 airworthiness criteria and recommended adding Sec. 33.70.
The FAA agrees and Sec. 33.70(a), (b), and (c) have been added to the
airworthiness criteria. The introductory paragraph of Sec. 33.70,
however, is not part of the airworthiness criteria.
A commenter also requested that the FAA specifically address high-
cycle fatigue (HCF) effects in proposed AM1.2713. The FAA notes that
HCF effects are included in the life limit calculation under Sec.
33.70. The influence of HCF on life limits is addressed as part of the
vibration requirement in AM1.2720, which characterizes and quantifies
all vibration stresses in a part. It also requires the vibration
stresses to be less than the material endurance limits, when combined
with steady stresses. No changes were made as a result of this comment.
A commenter noted that the FAA has historically not applied the
classification of ``critical part'' in FAA airworthiness standards and
asked for clarification. The use of critical parts is consistent with
the FAA's certification approach for electric engines and is necessary
for an acceptable level of safety. No changes were made as a result of
this comment.
One commenter questioned why the FAA included transient maximum
overtemperature and transient maximum overspeed as part of the
endurance demonstration in proposed AM1.2721. The FAA notes that
electric engines typically establish power or thrust ratings using
shaft torque. Therefore, torque is managed directly, or by another
governing parameter, such as electrical current. The airworthiness
criteria in AM1.2721 are performance-based, but the applicant may use
the procedures in Sec. 33.84(a) as a means of compliance with the
overtorque requirement. Transient rotor speed in electric and
combustion engines is controlled by different technologies. Transient
overspeed in a combustion engine is typically a design feature that
allows an engine to exceed a maximum steady state rotor speed
temporarily in order to meet certain performance requirements. Electric
engines use electrical current and have fast response times, so
transient rotor overspeed is not typically needed to meet performance
requirements and would most likely occur from a failure or design flaw,
which are occurrences within the scope of AM1.2721. No changes were
made as a result of this comment.
The FAA received a comment requesting clarity on the endurance
demonstration requirement in proposed AM1.2723(b). The FAA notes that
the endurance demonstration is an accelerated severity test intended to
demonstrate the engine has acceptable performance characteristics
throughout the operating range, up to and including engine ratings and
operating limits without the need for maintenance after being exposed
to these extreme conditions. Therefore, the engine cycles that are used
for the endurance demonstration do not correlate well with the engine
cycles that are used during in-service operation. The FAA concurs with
the commenter that additional clarification is needed and modified
AM1.2723(b) to require that the endurance demonstration must be for a
duration sufficient to verify the limit capabilities of the engine.
One commenter identified a need for clarification regarding
electromagnetic stresses in proposed AM1.2712, ``Stress Analysis,''
which also corresponds to Sec. 33.62. The FAA has updated AM1.2712(a)
to address the interaction between electrical systems and magnetic
components, specifically considering electromagnetic forces, which are
not covered in existing airworthiness standards for aircraft engines.
The revised paragraph (a) requires a
[[Page 45963]]
comprehensive stress analysis, including mechanical, thermal, and
electromagnetic forces, to ensure an adequate design margin that
prevents hazardous engine effects and unacceptable operating
characteristics.
Another commenter requested that the FAA add ``at the declared
operating limits'' to proposed AM1.2712(a). The FAA does not concur.
AM1.2712 includes mechanical, thermal, and electromagnetic stress.
These criteria were created to account for design limits specific to
electric engines that, if exceeded, could develop into hazardous engine
conditions. The airworthiness criteria ensure design margins account
for any relevant declared operating limits. No changes were made as a
result of this comment.
A commenter asked for clarification of the term ``minimum material
properties'' in proposed AM1.2712(b). AM1.2712(b) requires determining
maximum stresses in the engine without exceeding minimum material
properties. The Model M001 must comply with Sec. 33.15, which
establishes the requirements for engine materials. Compliance with
Sec. 33.15 will determine ``minimum material properties.'' No changes
were made as a result of this comment.
One commenter proposed that the FAA consider that the single fault
tolerance criteria in proposed AM1.2710(f)(2) be understood at the
aircraft ``propulsion system level'' rather than at the engine level
when addressing Loss of Power Control (LOPC). Commenters requested
similar clarification regarding the single fault criteria in proposed
AM1.2733(f)(2). The FAA disagrees that the requested change would be
appropriate. The airworthiness criteria in Subpart H apply to a single
engine, not to the entire distributed propulsion system. No changes
were made to the airworthiness criteria in response to these comments.
Multiple commenters requested that the FAA qualitatively and
quantitively define LOPC in the airworthiness criteria. The FAA does
not agree. The LOPC airworthiness criteria for the Model M001 are
contained in portions of Sec. 33.28 and AM1.2710. Existing engine
airworthiness standards in part 33 do not prescribe the level of detail
requested by the commenters. LOPC will depend on the performance data
and system analysis for the Model M001 and its intended aircraft
application. No changes were made as a result of these comments.
One commenter noted that Sec. 33.28(d)(4) effectively requires
that the engine control system be resilient to local events, while the
proposed airworthiness criteria in AM1.2710(f)(4) does not allow local
events to occur. The commenter requested the FAA revise AM1.2710(f)(4)
to maintain the safety intent of Sec. 33.28(d)(4). The FAA agrees with
the suggested change. AM1.2710(f)(4) has been changed to require the
engine control system to ``ensure failures or malfunctions that lead to
local events in the aircraft do not result in hazardous engine effects
as defined in AM1.2717(d)(2) due to engine control system failures or
malfunctions.''
One commenter proposed that the FAA differentiate between the
ingestions that must not lead to a hazardous event (such as a large
bird impact) and the ones that cannot lead to a loss of power that
would become incompatible with the aircraft performances and CSFL
capabilities. Another commenter questioned the use of the broad term
``foreign objects'' in proposed AM1.2718. The FAA modified AM1.2718 to
incorporate ingestion sources identified in Sec. Sec. 33.68, 33.76,
33.77, and 33.78. Revised AM1.2718 uses general terminology when
distinguishing abnormal operation, hazardous engine effects, and
unacceptable power loss which accounts for aircraft level effects and
clarifies the term ``foreign objects'' by specifying the ingestion
source.
Multiple commenters requested clarification regarding applicability
differences between Sec. 33.28 and proposed AM1.2710. The FAA notes
that the applicability of both requirements is covered by AM1.2710(a).
The FAA intends the applicant to employ the elements of Sec. 33.28
specified as applicable to the Model M001 in combination with the
additional requirements of AM1.2710.
Another commenter requested the FAA clarify whether Sec. 33.29(f)
applies to the Model M001. Section 33.29(f) requires a safety
assessment of incorrect fit of instruments, sensors, or connectors, and
references a Sec. 33.75 turbine engine safety analysis that is not
applicable to the Archer M001 electric engines. The airworthiness
criteria have been revised to exclude paragraph (f) from the
requirement to comply with certain paragraphs of Sec. 33.29.
One commenter asked if compliance with Sec. 33.64 is necessary to
satisfy the proposed pressurized cooling requirements in Sec. 33.21
and AM1.2706, as stated in ASTM Standard F3338-21 section 5.7.4. The
ASTM Standard applies to liquid engine cooling systems, but the
requirements in Sec. 33.21 and AM1.2706 apply to air and liquid engine
cooling systems. The FAA notes that although Sec. 33.64, which
contains requirements for pressurized engine static parts, is not part
of the Archer airworthiness criteria, pressurized engine static parts
are addressed by AM1.2719. Paragraph (a) specifies requirements for
systems used for lubrication or cooling engine components. Paragraph
(c) includes airworthiness criteria for static parts subjected to
pressurized systems. The FAA also revised the heading of AM1.2719 from
``Liquid Systems'' to ``Liquid and Gas Systems'' to clarify the
applicability of the requirement and to differentiate it from ASTM
Standard F3338-21.
Another commenter requested the FAA generalize the terminology in
proposed AM1.2728 to recognize electro-mechanical implementations in
addition to traditional mechanisms and functions. The commenter
proposed replacing ``locking'' with ``holding'' and ``unlocking'' with
``release.'' AM1.2728 does not prescribe specific implementation of the
rotor lock, other than the prevention of the rotor from turning. A
rotor locking (or holding) function in an electric engine could have
both mechanical and electro-mechanical purposes. The FAA determined the
criteria in AM1.2728 will achieve the intended objectives for the Model
M001. No changes are necessary as a result of the comment.
A commenter questioned the use of service limits in determining
acceptability during the teardown evaluation in proposed
AM1.2729(a)(1), as the service limits can be lower than those
demonstrated as a part of the certification process. The FAA agrees
that the intent is that each engine part must conform to the type
design and be eligible for incorporation into an engine for continued
operation and updated AM1.2729(a)(1) to remove the reference to service
limits.
The FAA received multiple comments asking to define or qualify what
would be an acceptable margin for purposes of proposed AM1.2730(a) and
whether a rotor burst analysis is required at the aircraft level. The
FAA disagrees. The FAA will determine an acceptable margin similar to
the way the agency determines acceptable margins for engines under part
33. No changes were made as a result of these comments.
In regard to compliance with the functional demonstrations required
by proposed AM1.2731, a commenter asked whether there will be a basic
standard test-run program, or whether the demonstration will depend on
the individual case. The FAA notes that AM1.2731 uses performance-based
language to describe the functional demonstrations if they are not
[[Page 45964]]
accomplished concurrent with other required engine tests. Currently,
there are no industry-wide accepted standards for conducting electric
engine tests with variable pitch propellers, so the demonstration will
depend on the individual case.
A commenter requested the FAA merge proposed AM1.2733(c)(1), which
addresses the electrical-power distribution system, and proposed
AM1.2733(d)(1), which addresses protection systems. Paragraph (c)
addresses the safe transfer of power throughout the power plant whereas
paragraph (d) addresses a protection system's response to power
conditions that exceed design limits. These systems perform different
functions, and therefore they are treated by separate airworthiness
criteria. No changes were made as a result of the comment.
The same commenter noted that the type of electrical fault
isolation required in proposed AM1.2733(c)(3) should be linked to the
possible effects of the fault on the safety of flight and the aircraft.
AM1.2733(c) protects engine electrical systems from faulted electrical
energy generation or storage devices. The means of compliance should be
tied to the safety assessment, which includes aircraft-level effects
from faulted electrical-energy generation or storage device. The FAA
updated AM1.2733(c)(3) to recognize this link.
A commenter questioned the numbering scheme of the airworthiness
criteria in proposed AM1.2733(d). The FAA agrees that the numbering
scheme needed better clarity. AM1.2733(d)(1) was merged with the
introductory text of AM1.2733(d). Proposed AM1.2733(d)(2) does not fit
under Protection Systems and was moved to AM1.2733(e). Proposed
AM1.2733(e) through (g) have been renumbered as AM1.2733(f) through
(h).
The same commenter noted that proposed AM1.2733(d) was too
prescriptive in specifically requiring transmission interruption. The
FAA agrees and changed the language to reflect that the Model M001 must
be designed such that certain conditions would not result in a
hazardous engine effect.
Lastly, the commenter requested that the FAA revise proposed
AM1.2733(e), which addresses environmental limits, to make it less
prescriptive. The commenter suggested that proposed AM1.2733(e) contain
similar language as that in the equivalent requirement for the
propeller control system in AM1.2823(a)(2). The FAA disagrees.
AM1.2733(e) and AM1.2823(a)(2) are not equivalent requirements as
stated by the commenter. Proposed AM1.2733(e) (AM1.2733(f) in these
final criteria) requires demonstrating environmental limits through
system and component tests when substantiation methods are
insufficient, while AM1.2823(a)(2) requires ensuring propeller control
system functionality remains unaffected by declared environmental
conditions and documenting validated environmental limits in propeller
manuals. No changes were made as a result of this comment.
Propellers
The FAA received and reviewed comments from ALPA, Airbus, ASD-
Europe, EASA, GAMA, Leonardo, Overair, TCCA, and Volocopter requesting
the FAA revise, remove, or clarify proposed airworthiness criteria
related to propellers for the Model M001.
Multiple commenters requested changes to proposed AM1.2823
regarding the causal direction of hazardous propeller effects and local
events. The FAA concurs and has revised AM1.2823(b)(2) to require that
local events not cause hazardous propeller effects. One commenter
suggested that ``local event'' needs to be defined. Due to the comments
received on ``local events,'' the FAA concurs that the definition of
``local events,'' in the context of AM1.2823, should be as defined as
it is in AC 33.28-3, ``Guidance Material for 14 CFR 33.28, Engine
Control Systems,'' with minor wording changes that are appropriate for
the Model M001. The FAA has added this definition to AM1.2000(b)(6).
The FAA noted during review of AM1.2823 that two requirements from
Sec. 35.23 were missing in the proposed airworthiness criteria and
should be added. The FAA added Sec. Sec. 35.23(b)(3) and 35.23(b)(4)
to the airworthiness criteria as paragraphs AM1.2823(b)(3) and
AM1.2823(b)(4).
One commenter asked why the functional test in proposed AM1.2840 is
limited to forward pitch and not to the entire pitch range. The FAA
notes that the test is limited because the Model M001 does not have
reversible pitch capability. Additionally, commenters suggested that
the number of propeller pitch cycles should be increased from thirteen
hundred to fifteen hundred in proposed AM1.2840(a) to align it with
Sec. 35.40(b). The FAA agrees and has revised AM1.2840(a) accordingly.
Several commenters requested the FAA elaborate on how the FAA
differentiated between requirements for lift generating rotors compared
to propellers, and whether icing ingestion requirements are needed for
propellers. The FAA does not concur with suggestions to add additional
requirements for lift generating rotors or ice ingestion requirements
for the AM1.2800 series criteria. The design and the expected failure
modes of Archer's propellers are expected to be similar to conventional
propellers type certificated under part 35 despite being used in the
vertical thrust mode. Ice ingestion requirements for the engines
already exist in other parts of the Model M001 airworthiness criteria.
Commenters suggested that proposed AM1.2815, which requires a
safety analysis of the propeller system, is inadequate because the rate
of hazardous propeller effects was not conservative enough and
propeller release and unbalance should be treated as catastrophic
events and not as hazardous propeller effects. Further, commenters
suggested that determining the rate of hazardous propeller effects
should be less ambiguous. The FAA does not concur with the suggestion
that the acceptable hazardous propeller failure rate is too high. The
criteria are derived from part 35 requirements, which provide an
acceptable level of safety for both part 23 and 25 airplanes. The FAA
does not concur with the suggestion that propeller release and
unbalance should be treated as catastrophic and not hazardous effects.
Catastrophic effects are treated at the aircraft level and the criteria
for single propellers provide an acceptable level of safety. The FAA
does not concur with the request to make the quantitative prediction of
a hazardous propeller effect less ambiguous due to inherent limitations
on the availability of reliable data.
One commenter questioned the need for a propeller critical part
designation. The FAA does not concur with the suggestion to not make
the propellers critical parts. The critical part requirements are
integral for creating a propeller with an equivalent level of safety
and are retained for the Model M001.
Commenters suggested that the current Sec. 35.35 centrifugal load
requirements are inappropriately prescriptive and that overspeed
requirements derived from parts 27 or 29 rotorcraft rules are more
appropriate. The FAA does not concur with the suggestion to substitute
rotorcraft overspeed requirements for the propeller centrifugal load
tests in Sec. 35.35(a) and (b) because the design and failure modes of
Archer's propellers are expected to be similar to conventional
propellers type certificated under part 35. The consequential propeller
loads are expected to primarily be centrifugal loads, and therefore the
prescriptive centrifugal
[[Page 45965]]
test requirement of Sec. 35.35, with its requirement for a large
margin of safety, is needed to ensure an equivalent level of safety.
A commenter stated that the propeller-specific lightning strike
requirements of Sec. 35.38, which prevent major or hazardous effects,
are inconsistent with aircraft-level lightning requirements in
AM1.2335, which prevents catastrophic effects. The commenter proposed
modifying the airworthiness criteria to remove the inconsistency. The
FAA disagrees. The propeller requirements prescribe a particular safety
level for an uninstalled propeller only; an uninstalled propeller does
not need the same safety requirements as the aircraft. The aircraft
safety analysis uses the propeller failure rate data to show that the
aircraft will not experience any catastrophic effects. No changes were
made as a result of this comment.
One commenter requested a definition for maximum propeller
overspeed and overtorque as used in Sec. 35.41. The FAA does not
concur with the request to define propeller overspeed or overtorque
because the applicant defines these ratings, if applicable, to show
compliance with AM1.2805 and Sec. 35.41. No changes were made as a
result of this comment.
Another commenter requested a definition of acceptable ``propellers
of similar design'' for purposes of compliance with AM1.2840(c). By a
propeller of ``similar design'' in AM1.2840(c), the FAA means that
expected failure modes, materials, construction, normal operating
characteristics, and features of the propeller are unchanged or have
only insignificant differences compared to another propeller. No
changes were made as a result of this comment.
Requests To Include Additional Criteria
The FAA received comments from Airbus, ALPA, ASD-Europe, EASA,
GAMA, IPR, Lilium, and TCCA, that additional criteria should be added
for the Model M001 powered-lift.
One commenter requested the FAA provide reasoning on the omission
of Sec. 23.2005, which defines certification levels for normal
category airplanes based on maximum seating configuration and speed, or
an equivalent airworthiness criterion. The commenter requested the FAA
discuss how the agency is establishing the minimum safety requirements
for various special class powered-lift products to provide an
equivalent level of safety. The FAA did not include Sec. 23.2005 in
these airworthiness criteria as that regulation was developed
specifically for part 23 airplanes, and the Model M001 is a powered-
lift with novel flight phases that are not representative of airplanes;
instead, the FAA is establishing a level of safety for the Model M001
that is equivalent with the level of safety in both part 23 and part 27
for airplanes and rotorcraft performing similar operations.
Additionally, the criteria in this notice are specific for the Model
M001 and are not generally applicable to powered-lift of various sizes.
An individual requested more criteria for HIRF environment applied
to urban air mobility operations and vertiports. The FAA notes
AM1.2520(a), HIRF protection, requires compliance for systems
associated with catastrophic failure conditions. No changes were made
as a result of this comment.
Several commenters requested the FAA require provisions for in-
service monitoring such as a Health and Usage Monitoring System (HUMS)
system to validate assumptions pertaining to airframe structure
designs. The FAA is charged under Sec. 21.17(b) to provide an
equivalent level of safety to the existing airworthiness standards. The
FAA does not currently require in-service monitoring for critical parts
on other aircraft types, and the FAA does not plan to require any
provisions for in-service monitoring of critical parts for powered-
lift. No changes were made as a result of these comments.
Several commenters noted that no specific requirement is mentioned
for aircraft batteries and recommended the FAA create new, specific
criteria to address topics such as fire protection, fire propagation,
crashworthiness, high-voltage current disconnection, protection from
lightning transients, punctures and leakage of toxic gas or liquid, and
effects of temperature and battery health on battery performance. The
FAA acknowledges the risk posed by these hazards but does not agree
that additional specific requirements are necessary. All risks
identified are adequately addressed by the requirements of Subparts E
and F, AM1.1529, and the Appendix A ICA requirements for airframe,
engines, and propellers, with specific safety objectives and means of
compliance to address these risks that will be developed and tailored
to the specific aspects of the Model M001 powered-lift.
Out of Scope Comments
The FAA received and reviewed numerous comments that were general,
stated the commenter's viewpoint or opposition without a suggestion
specific to the proposed criteria, did not make a request the FAA can
act on, requested clarification on existing airworthiness standards,
requested changes or clarification to means of compliance, requested
changes to type certification procedures defined in 14 CFR part 21,
requested requirements for features not included on the Model M001,
improperly assumed the Model M001 was an Unmanned Aircraft System,
addressed issues covered by operational requirements including IFR
under which the Model M001 will not be operating or other 14 CFR parts
not related to airworthiness, or asked generalized questions about the
Model M001 powered-lift. These comments are beyond the scope of this
document. The FAA also reviewed several comments relating to the
pursuit of future rulemaking for powered-lift, which is beyond the
scope of these airworthiness criteria.
Additional Changes Made to the Proposed Criteria
From October 31, 2023, through November 2, 2023, the FAA met with
representatives from EASA regarding the proposed airworthiness
criteria. This discussion did not pertain specifically to the Model
M001, but instead concerned harmonization activities between EASA and
the FAA on the requirements and means of compliance for type
certification of powered-lift/VTOL aircraft generally. As a result of
this meeting, and for consistency with the harmonized general criteria,
the FAA changed the proposed requirement to comply with Sec.
23.2250(c). The FAA added the sentence ``The applicant must prevent
single failures from resulting in a catastrophic effect upon the
aircraft'' to Sec. 23.2250(c) (now AM1.2250(c)) to clarify that while
single point failures are allowed in the design, they must be prevented
from resulting in a catastrophic effect on the aircraft.
Applicability
These airworthiness criteria, established under the provisions of
Sec. 21.17(b), are applicable to the Archer Model M001 powered-lift.
Should Archer apply at a later date for a change to the type
certificate to include another model, these airworthiness criteria
would apply to that model as well, provided the FAA finds them
appropriate in accordance with the requirements of subpart D to part
21.
Conclusion
This action affects only certain airworthiness criteria for the
Model M001 powered-lift. It is not a standard of general applicability.
[[Page 45966]]
Authority Citation
The authority citation for these airworthiness criteria is as
follows:
Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.
Airworthiness Criteria
Pursuant to the authority delegated to me by the Administrator, the
following airworthiness criteria are issued as part of the type
certification basis for the Model M001 powered-lift. The FAA finds
these criteria to be appropriate for the aircraft and applicable to the
specific type design and provide an equivalent level of safety to
existing airworthiness standards.
Aircraft-Level Requirements
Sec. 23.1457 Cockpit Voice Recorders
(a) through (g) [Applicable to Model M001]
Sec. 23.1459 Flight Data Recorders
(a) through (e) [Applicable to Model M001]
AM1.1529 Instructions for Continued Airworthiness
The applicant must prepare Instructions for Continued Airworthiness
(ICA), in accordance with Appendices A, A1, and A2, that are acceptable
to the Administrator. ICA for the aircraft, engines, and propellers may
be shown in a single aircraft ICA manual if the engine and propeller
approvals are sought through the aircraft certification program.
Alternatively, the applicant may provide individual ICA for the
aircraft, engines, and propellers. The instructions may be incomplete
at the time of type certification if a program exists to ensure their
completion prior to delivery of the first aircraft, or issuance of a
standard certificate of airworthiness, whichever occurs later.
Subpart A--General
AM1.2000 Applicability and Definitions
(a) These airworthiness criteria prescribe airworthiness standards
for the issuance of a type certificate, and changes to that type
certificate, for the Archer Aviation, Inc. Model M001 powered-lift.
This aircraft must be certificated in accordance with either the
``essential performance'' or ``increased performance'' requirements of
these airworthiness criteria. This aircraft may also be type
certificated as both ``essential performance'' and ``increased
performance'' with appropriate and different operating limitations for
each approval.
(b) For purposes of these airworthiness criteria, the following
definitions apply:
(1) Continued safe flight and landing--
(i) for powered-lift approved for ``essential performance'' means
the aircraft is capable of continued controlled flight and landing,
possibly using emergency procedures, without requiring exceptional
pilot skill, strength, or alertness.
(ii) for powered-lift approved for ``increased performance'' means
the aircraft is capable of climbing to a safe altitude, on a flightpath
clear of obstacles, and maintaining level flight to a planned
destination or alternate landing, possibly using emergency procedures,
without requiring exceptional pilot skill, strength, or alertness.
(2) Phases of flight means ground operations, takeoff, climb,
cruise, descent, approach, hover, and landing.
(3) Source of lift means one of three sources of lift:
thrust[hyphen]borne, wing[hyphen]borne, and semi-thrust[hyphen]borne.
Thrust[hyphen]borne is defined as when the weight of the aircraft is
principally supported by lift generated by engine-driven lift devices.
Wing[hyphen]borne is defined as when the weight of the aircraft is
principally supported by aerodynamic lift from fixed airfoil surfaces.
Semi[hyphen]thrust[hyphen]borne is the combination of
thrust[hyphen]borne and wing[hyphen]borne, where both forms of lift are
used to support the weight of the aircraft.
(4) Controlled emergency landing means the aircraft design retains
the capability to allow the pilot to choose the direction and area of
touchdown while reasonably protecting occupants from serious injury.
Upon landing, some damage to the aircraft may be acceptable.
(5) Critical change of thrust means the most adverse effect on
performance or handling qualities resulting from failures of the flight
control or propulsive system, either singular or in combination, not
shown to be extremely improbable.
(6) Local events are failures of aircraft systems and components,
other than the engine and propeller control system, that may affect the
installed environment of the engine and propeller control system.
(c) Terms used in the part 23, part 33, and part 35 provisions that
are adopted in these airworthiness criteria will have the following
meaning:
``Airplane'' means ``aircraft.''
``This part'' means ``these airworthiness criteria.''
``Rotorcraft'' means ``aircraft.''
Sec. 23.2010 Accepted Means of Compliance
(a) through (b) [Applicable to Model M001]
Subpart B--Flight
Performance
Sec. 23.2100 Weight and Center of Gravity
(a) through (c) [Applicable to Model M001]
AM1.2105 Performance Data
(a) Unless otherwise prescribed, the aircraft must meet the
performance requirements of this subpart in still air and standard
atmospheric conditions.
(b) Unless otherwise prescribed, the applicant must develop the
performance data required by this subpart for the following conditions:
(1) Altitudes from sea level to the maximum altitude for which
certification is being sought.; and
(2) Temperatures above and below standard day temperature that are
within the range of operating limitations, if those temperatures could
have a negative effect on performance.
(c) The procedures used for determining takeoff and landing
performance must be executable consistently by pilots of average skill
in atmospheric conditions expected to be encountered in service.
(d) Performance data determined in accordance with paragraph (b) of
this section must account for losses due to atmospheric conditions,
cooling needs, installation losses, downwash considerations, and other
demands on power sources.
(e) The hovering ceiling, in and out of ground effect, must be
determined over the ranges of weight, altitude, and temperature, if
applicable.
(f) Continued safe flight and landing must be possible from any
point within the approved flight envelope following a critical change
of thrust.
(g) The aircraft must be capable of a controlled emergency landing,
following a condition when the aircraft can no longer provide the
commanded power or thrust required for continued safe flight and
landing, by gliding or autorotation, or an equivalent means to mitigate
the risk of loss of power or thrust.
AM1.2110 Minimum Safe Speed
The applicant must determine the aircraft minimum safe speed for
each flight condition encountered in normal operations, including
applicable sources of lift and phases of flight, to maintain controlled
safe flight. The minimum safe speed determination must account
[[Page 45967]]
for the most adverse conditions for each flight configuration.
AM1.2115 Takeoff Performance
(a) The applicant must determine takeoff performance accounting
for:
(1) All sources of lift for each takeoff flight path for which
certification is sought,
(2) Minimum safe speed safety margins,
(3) Minimum control speeds, and
(4) Climb requirements.
(b) For aircraft approved for essential performance, the applicant
must determine the takeoff performance to 50 feet above the takeoff
surface such that a rejected takeoff resulting in safe stop or landing
can be made at any point along the takeoff flight path following a
critical change of thrust.
(c) For aircraft approved for increased performance, the applicant
must determine the takeoff performance so that--
(1) Following a critical change of thrust prior to reaching the
takeoff decision point, a rejected takeoff resulting in a safe stop or
landing can be made. The takeoff decision point may be a speed, an
altitude, or both.
(2) Following a critical change of thrust after passing the takeoff
decision point, the aircraft can--
(i) Continue the takeoff and climb to 50 feet above the takeoff
surface; and
(ii) Subsequently achieve the configuration and airspeed used in
compliance with AM1.2120.
AM1.2120 Climb Requirements
(a) The applicant must demonstrate minimum climb performance at
each weight, altitude, and ambient temperature within the operating
limitations using the procedures published in the flight manual.
(b) For aircraft approved for essential and increased performance,
the applicant must determine the following all engines operating (AEO)
climb performance requirements:
(1) A steady climb gradient at sea level of at least 8.3 percent in
the initial takeoff configuration(s) and a climb speed selected by the
applicant or Vy, and
(2) For a balked landing, a climb gradient of 3 percent without
creating undue pilot workload with the landing gear extended and flaps
in the landing configuration(s).
(c) For aircraft approved for essential performance, the climb
performance after a critical change of thrust must be determined--
(1) Using applicable sources of lift along the takeoff flight path
for which certification is being sought at the speeds and
configurations selected by the applicant; and
(2) For the transition from the takeoff to the enroute
configuration. The total altitude loss must be determined for the
weight, altitude, and ambient temperature where level flight cannot be
maintained.
(d) For aircraft approved for increased performance, the climb
performance after a critical change of thrust must be such that--
(1) In thrust-borne and semi-thrust-borne flight:
(i) The steady rate of climb without ground effect, 200 feet above
the takeoff surface, is at least 100 feet per minute,
(ii) The steady rate of climb without ground effect, 1000 feet
above the takeoff surface, is at least 150 feet per minute,
(iii) The steady rate of climb (or descent) enroute is determined
in feet per minute, at each weight, altitude, and temperature at which
the aircraft is expected to operate for which certification is
requested.
(2) In wing-borne flight, the steady gradient of climb:
(i) During takeoff at the takeoff surface, is at least 0.5 percent
with the aircraft in its takeoff configuration(s),
(ii) During takeoff at 400 feet above the takeoff surface, is at
least 2.6 percent with the aircraft in its second segment
configuration,
(iii) Enroute at 1,500 feet above the takeoff or landing surface,
as appropriate, is at least 1.7 percent with the aircraft in a cruise
configuration, and
(iv) During a discontinued approach at 400 feet above the landing
surface, is not less than 2.7 percent in an approach configuration.
(e) The applicant must determine the performance accordingly for
the appropriate sources of lift for gliding, autorotation, or the
equivalent means established under AM1.2105(g).
AM1.2125 Climb Information
(a) The applicant must determine climb performance at each weight,
altitude, and ambient temperature within the operating limitations
using the procedures published in the flight manual.
(b) The applicant must determine climb performance accounting for
any critical change of thrust.
AM1.2130 Landing
The applicant must determine the following, for standard
temperatures at critical combinations of weight and altitude within the
operational limits:
(a) The approach and landing speeds and procedures, which allow a
pilot of average skill to land within the published landing distance
consistently and without causing damage or injury, and which allow for
a safe transition to the balked landing conditions of these
airworthiness criteria accounting for:
(1) All sources of lift for each approach and landing flight path
for which certification is sought,
(2) Any minimum or maximum speed safety margins, and
(3) Minimum control speeds.
(b) For aircraft approved for essential performance, the applicant
must determine the landing performance from a height of 50 feet above
the landing surface. Additionally, the aircraft must be capable of
performing a safe landing at any point along the approach flight path
following a critical change of thrust.
(c) For aircraft approved for increased performance, the applicant
must determine the landing performance from a height of 50 feet above
the landing surface so that, following a critical change of thrust that
occurs prior to the landing decision point, the aircraft can-
(1) Land and stop safely on the landing surface; or
(2) Transition to the balked landing condition and performance
established in AM1.2120.
Flight Characteristics
AM1.2135 Controllability
(a) The aircraft must be controllable and maneuverable, without
requiring exceptional piloting skill, alertness, or strength, within
the approved flight envelope--
(1) At all loading conditions for which certification is requested;
(2) During all phases of flight while using applicable sources of
lift;
(3) With likely flight control or propulsion system failure;
(4) During configuration changes;
(5) In all degraded flight control system operating modes not shown
to be extremely improbable;
(6) In thrust-borne operation, and must be controllable in wind
velocities from zero to at least 17 knots from any azimuth angle; and
(7) The aircraft must be able to safely complete a landing using
the steepest approach gradient procedures.
(b) The applicant must determine critical control parameters, such
as limited control power margins, and if applicable, account for those
parameters in appropriate operating limitations.
(c) It must be possible to make a smooth transition from one flight
condition to another (changes in configuration and in source of lift
and phase of flight) without exceeding the approved flight envelope.
[[Page 45968]]
AM1.2140 Trim
(a) The aircraft must maintain lateral and directional trim without
further force upon, or movement of, the primary flight controls or
corresponding trim controls by the pilot, or the flight control system,
under all normal operations while using applicable sources of lift.
(b) The aircraft must maintain longitudinal trim without further
force upon, or movement of, the primary flight controls or
corresponding trim controls by the pilot, or the flight control system,
under the following conditions:
(1) Climb.
(2) Level flight.
(3) Descent.
(4) Approach.
(c) Residual control forces must not fatigue or distract the pilot
during normal operations of the aircraft and likely abnormal or
emergency operations, including a critical change of thrust.
AM1.2145 Stability
(a) The aircraft must exhibit static stability characteristics
inclusive of likely failures.
(b) The aircraft must exhibit suitable short period dynamic
stability inclusive of likely failures.
(c) For wing borne and semi-thrust-borne operations:
(1) No aircraft may exhibit any divergent longitudinal dynamic
stability characteristics so unstable as to increase the pilot's
workload or otherwise endanger the aircraft and its occupants, and
(2) The aircraft must exhibit lateral-directional dynamic stability
inclusive of likely failures.
(d) For thrust borne operations, no aircraft may exhibit any
divergent dynamic stability characteristics so unstable as to increase
the pilot's workload or otherwise endanger the aircraft and its
occupants.
AM1.2150 Minimum Safe Speed Characteristics and Warning
(a) When part of the lift is generated from a fixed wing, the
aircraft must have controllable stall characteristics in straight
flight, turning flight, and accelerated turning flight with a clear and
distinctive stall warning that provides sufficient margin to prevent
inadvertent stalling and not have a tendency to inadvertently depart
controlled safe flight.
(b) For other sources of lift, the aircraft must have controllable
characteristics in straight flight, turning flight, and accelerated
turning flight with a clear and distinctive warning that provides
sufficient margin to prevent inadvertent departures from controlled
safe flight.
(c) For all sources of lift, the aircraft must not have the
tendency to inadvertently depart controlled safe flight after a sudden
change of thrust.
Sec. 23.2155 Ground and Water Handling Characteristics
[Applicable to Model M001]
AM1.2160 Vibration, Buffeting, and High-Speed Characteristics
(a) Each part of the aircraft must be free from excessive vibration
and buffeting under each appropriate speed and power condition.
Vibration and buffeting, for operations up to VD/
MD, must not interfere with the control of the aircraft or
cause excessive fatigue to the flightcrew. Stall warning buffet within
these limits is allowable.
(b) For inadvertent excursions beyond the maximum approved speed,
the aircraft must be able to safely recover back to its approved flight
envelope without requiring exceptional piloting skill, strength, or
alertness. This recovery may not result in structural damage or loss of
control.
AM1.2165 Performance and Flight Characteristics Requirements for Flight
in Atmospheric Icing Conditions
(a) The applicant must provide a means to detect icing conditions
for which certification is not requested and show the aircraft's
ability to avoid or exit those icing conditions.
(b) The applicant must develop an operating limitation to prohibit
intentional flight, including takeoff and landing, into icing
conditions for which the aircraft is not certified to operate.
Subpart C--Structures
AM1.2200 Structural Design Envelope
The applicant must determine the structural design envelope, which
describes the range and limits of aircraft design and operational
parameters for which the applicant will show compliance with the
requirements of this subpart. The applicant must account for all
aircraft design and operational parameters that affect structural
loads, strength, durability, and aeroelasticity, including:
(a) Structural design airspeeds, landing descent speeds, and any
other airspeed limitation at which the applicant must show compliance
to the requirements of this subpart. The structural design airspeeds
must--
(1) Be sufficiently greater than the minimum safe speed of the
aircraft to safeguard against loss of control in turbulent air; and
(2) Provide sufficient margin for the establishment of practical
operational limiting airspeeds.
(b) Design maneuvering load factors not less than those, which
service history shows, may occur within the structural design envelope.
(c) Inertial properties including weight, center of gravity, and
mass moments of inertia, accounting for--
(1) Each critical weight from the aircraft empty weight to the
maximum weight; and
(2) The weight and distribution of occupants, payload, and energy-
storage systems.
(d) Characteristics of aircraft control systems, including range of
motion and tolerances for control surfaces, high lift devices, or other
moveable surfaces.
(e) Each critical altitude up to the maximum altitude.
(f) Engine-driven lifting-device rotational speed and ranges, and
the maximum rearward and sideward flight speeds.
(g) Thrust[hyphen]borne, wing[hyphen]borne, and
semi[hyphen]thrust[hyphen]borne flight configurations, with associated
flight load envelopes.
Sec. 23.2205 Interaction of Systems and Structures
[Applicable to Model M001]
Structural Loads
Sec. 23.2210 Structural Design Loads
(a) through (b) [Applicable to Model M001]
AM1.2215 Flight Load Conditions
(a) The applicant must determine the structural design loads
resulting from the following flight conditions:
(1) Atmospheric gusts where the magnitude and gradient of these
gusts are based on measured gust statistics.
(2) Symmetric and asymmetric maneuvers.
(3) Asymmetric thrust resulting from the failure of a powerplant
unit.
(b) There must be no vibration or buffeting severe enough to result
in structural damage, at any speed up to dive speed, within the
structural design envelope, in any configuration and power setting.
Sec. 23.2220 Ground and Water Load Conditions
[Applicable to Model M001]
AM1.2225 Component Loading Conditions
The applicant must determine the structural design loads acting on:
(a) Each engine mount and its supporting structure such that both
are
[[Page 45969]]
designed to withstand loads resulting from--
(1) Powerplant operation combined with flight gust and maneuver
loads; and
(2) For non-reciprocating powerplants, sudden powerplant stoppage.
(b) Each flight control and high-lift surface, their associated
system and supporting structure resulting from--
(1) The inertia of each surface and mass balance attachment;
(2) Flight gusts and maneuvers;
(3) Pilot or automated system inputs;
(4) System induced conditions, including jamming and friction; and
(5) Taxi, takeoff, and landing operations on the applicable
surface, including downwind taxi and gusts occurring on the applicable
surface.
(c) [Reserved]
(d) Engine-driven lifting-device assemblies, considering loads
resulting from flight and ground conditions, as well limit input torque
at any lifting-device rotational speed.
Sec. 23.2230 Limit and Ultimate Loads
(a) through (b) [Applicable to Model M001]
Structural Performance
Sec. 23.2235 Structural Strength
(a) through (b) [Applicable to Model M001]
AM1.2240 Structural Durability
(a) The applicant must develop and implement inspections or other
procedures to prevent structural failures due to foreseeable causes of
strength degradation, which could result in serious or fatal injuries,
or extended periods of operation with reduced safety margins. Each of
the inspections or other procedures developed under this section must
be included in the Airworthiness Limitations Section of the ICA,
required by AM1.1529.
(b) If safety-by-design (fail-safe) is used to comply with
paragraph (a) of this section, safety-by-inspection (damage tolerance)
must also be incorporated to reliably detect structural damage before
the damage could result in structural failure.
(c) The aircraft must be designed to minimize hazards to the
aircraft due to structural damage caused by high-energy fragments from
an uncontained engine or rotating machinery failure.
AM1.2241 Aeromechanical Stability
The aircraft must be free from dangerous oscillations and
aeromechanical instabilities for all configurations and conditions of
operation on the ground and in flight.
AM1.2245 Aeroelasticity
(a) The aircraft must be free from flutter, control reversal, and
divergence--
(1) At all speeds within and sufficiently beyond the structural
design envelope;
(2) For any configuration and condition of operation;
(3) Accounting for critical structural modes, and
(4) Accounting for any critical failures or malfunctions.
(b) The applicant must establish tolerances for all quantities that
affect aeroelastic stability.
(c) Each component and rotating aerodynamic surface of the aircraft
must be free from any aeroelastic instability under each appropriate
speed and power condition.
Design
AM1.2250 Design and Construction Principles
(a) The applicant must design each part, article, and assembly for
the expected operating conditions of the aircraft.
(b) Design data must adequately define the part, article, or
assembly configuration, its design features, and any materials and
processes used.
(c) The applicant must determine the suitability of each design
detail and part having an important bearing on safety in operations.
The applicant must prevent single failures from resulting in a
catastrophic effect upon the aircraft.
(d) The control system must be free from jamming, excessive
friction, and excessive deflection when the aircraft is subjected to
expected limit airloads.
(e) Doors, canopies, and exits must be protected against
inadvertent opening in flight, unless shown to create no hazard when
opened in flight.
Sec. 23.2255 Protection of Structure
(a) through (c) [Applicable to Model M001]
Sec. 23.2260 Materials and Processes
(a) through (g) [Applicable to Model M001]
Sec. 23.2265 Special Factors of Safety
(a) through (c) [Applicable to Model M001]
Structural Occupant Protection
Sec. 23.2270 Emergency Conditions
(a) through (e) [Applicable to Model M001]
Subpart D--Design and Construction
AM1.2300 Flight Control Systems
(a) The applicant must design flight control systems to:
(1) Operate easily, smoothly, and positively enough to allow proper
performance of their functions;
(2) Protect against likely hazards; and
(3) Ensure that the flightcrew is made suitably aware whenever the
means of primary flight control approaches the limits of control
authority.
(b) The applicant must design trim systems or trim functions, if
installed, to:
(1) Protect against inadvertent, incorrect, or abrupt trim
operation; and
(2) Provide information that is required for safe operation.
(c) Features that protect the aircraft against loss of control or
exceeding critical limits must be designed such that there are no
adverse flight characteristics in aircraft response to flight-control
inputs, unsteady atmospheric conditions, and other likely conditions,
including simultaneous limiting events.
Sec. 23.2305 Landing Gear Systems
(a) through (c) [Applicable to Model M001]
AM1.2311 Bird Strike
The aircraft must be capable of continued safe flight and landing
after impact with a 2.2-lb (1.0 kg) bird.
Occupant System Design Protection
AM1.2315 Means of Egress and Emergency Exits
(a) With the cabin configured for takeoff or landing, the aircraft
is designed to:
(1) Facilitate rapid and safe evacuation of the aircraft in
conditions likely to occur following an emergency landing.
(2) Have means of egress (openings, exits, or emergency exits),
that can be readily located and opened from the inside and outside. The
means of opening must be simple and obvious and marked inside and
outside the aircraft.
(3) Have easy access to emergency exits when present.
(b) [Reserved]
Sec. 23.2320 Occupant Physical Environment
(a) and (c) [Applicable to Model M001]
(b), (d), and (e) [Not applicable to Model M001]
Fire and High Energy Protection
AM1.2325 Fire Protection
(a) The following materials must be self-extinguishing--
(1) Insulation on electrical wire and electrical cable; and
[[Page 45970]]
(2) Materials in the baggage and cargo compartments inaccessible in
flight.
(b) The following materials must be flame resistant--
(1) Materials in each compartment accessible in flight; and
(2) Any equipment associated with any electrical cable installation
and that would overheat in the event of circuit overload or fault.
(c) Thermal/acoustic materials in the fuselage, if installed, must
not be a flame propagation hazard.
(d) Sources of heat within each baggage and cargo compartment that
are capable of igniting adjacent objects must be shielded and insulated
to prevent such ignition.
(e) Each baggage and cargo compartment must--
(1) Be located where a fire would be visible to the pilots and be
accessible for the manual extinguishing of a fire,
(2) Be equipped with a smoke or fire detection system that warns
the pilot, or
(3) Be constructed of, or lined with, fire resistant materials.
(f) There must be a means to extinguish any fire in the cabin such
that the pilot, while seated, can easily access the fire extinguishing
means.
(g) Each area where flammable fluids or vapors might escape by
leakage of a fluid system must--
(1) Be defined; and
(2) Have a means to minimize the probability of fluid and vapor
ignition, and the resultant hazard, if ignition occurs.
AM1.2330 Fire Protection in Fire Zones and Adjacent Areas
(a) Flight controls, engine mounts, and other flight structures
within or adjacent to fire zones must be capable of withstanding the
effects of a fire.
(b) Engines in a fire zone must remain attached to the aircraft in
the event of a fire.
(c) In fire zones, terminals, equipment, and electrical cables used
during emergency procedures must perform their intended function in the
event of a fire.
AM1.2335 Lightning and Static Electricity Protection
(a) The aircraft must be protected against catastrophic effects
from lightning.
(b) The aircraft must be protected against hazardous effects caused
by an accumulation of electrostatic charge.
Subpart E--Powerplant
AM1.2400 Powerplant Installation
(a) For the purpose of this subpart, the aircraft powerplant
installation must include each component necessary for propulsion,
which affects propulsion safety.
(b) Each aircraft engine and propeller must be approved under the
aircraft type certificate using standards found in subparts H and I.
(c) The applicant must construct and arrange each powerplant
installation to account for--
(1) Likely operating conditions, including foreign-object threats;
(2) Sufficient clearance of moving parts to other aircraft parts
and their surroundings;
(3) Likely hazards in operation including hazards to ground
personnel; and
(4) Vibration and fatigue.
(d) Hazardous accumulations of fluids, vapors, or gases must be
isolated from the aircraft and personnel compartments and be safely
contained or discharged.
(e) Powerplant components must comply with their component
limitations and installation instructions or be shown not to create a
hazard.
AM1.2405 Power or Thrust Control Systems
(a) Any power or thrust control system or powerplant control system
must be designed so no unsafe condition results during normal operation
of the system.
(b) Any single failure or likely combination of failures or
malfunctions of a power or thrust control system or powerplant control
system must not prevent continued safe flight and landing of the
aircraft.
(c) Inadvertent flightcrew operation of a power or thrust control
system or powerplant control system must be prevented, or if not
prevented, must not prevent continued safe flight and landing of the
aircraft.
Sec. 23.2410 Powerplant Installation Hazard Assessment
(a) through (c) [Applicable to Model M001]
Sec. 23.2415 Powerplant Ice Protection
(a) through (b) [Applicable to Model M001]
AM1.2425 Powerplant Operational Characteristics
(a) Each installed powerplant must operate without any hazardous
characteristics during normal and emergency operation within the range
of operating limitations for the aircraft and the engine.
(b) The design must provide for the shutdown and restart of the
powerplant in flight within an established operational envelope.
AM1.2430 Energy Systems
(a) Each energy system must--
(1) Be designed and arranged to provide independence between
multiple energy-storage and supply systems, so that failure of any one
component in one system will not result in loss of energy storage or
supply of another system;
(2) Be designed to prevent catastrophic events due to lightning
strikes, taking into account direct and indirect effects on the
aircraft;
(3) Provide the energy necessary to ensure each powerplant
functions properly in all likely operating conditions;
(4) Provide the flightcrew with a means to determine the total
useable energy available and provide uninterrupted supply of that
energy when the system is correctly operated, accounting for likely
energy fluctuations;
(5) Provide a means to safely remove or isolate the energy stored
in the system from the aircraft; and
(6) Be designed to retain energy under all likely operating
conditions and to minimize hazards to occupants and first responders
following an emergency landing or otherwise survivable impact (crash
landing).
(b) Each energy-storage system must--
(1) Withstand the loads under likely operating conditions without
failure; and
(2) Be isolated from personnel compartments and protected from
likely hazards.
(c) Each energy-storage recharging system must be designed to--
(1) Prevent improper recharging; and
(2) Prevent the occurrence of hazard to the aircraft or to persons
during recharging.
AM1.2440 Powerplant Fire Protection
There must be means to isolate and mitigate hazards to the aircraft
in the event of a powerplant system fire or overheat in operation.
Subpart F--Equipment
Sec. 23.2500 Airplane Level Systems Requirements
(a) through (b) [Applicable to Model M001]
Sec. 23.2505 Function and Installation
[Applicable to Model M001]
Sec. 23.2510 Equipment, Systems, and Installations
(a) through (c) [Applicable to Model M001]
[[Page 45971]]
AM1.2515 Electrical- and Electronic-System Lightning Protection
(a) Each electrical or electronic system that performs a function,
the failure of which would prevent the continued safe flight and
landing of the aircraft, must be designed and installed such that--
(1) The function at the aircraft level is not adversely affected
during and after the time the aircraft is exposed to lightning; and
(2) The system recovers normal operation of that function in a
timely manner after the aircraft is exposed to lightning unless the
system's recovery conflicts with other operational or functional
requirements of the system.
(b) For an aircraft approved for operation under instrument flight
rules (IFR), each electrical and electronic system that performs a
function, the failure of which would reduce the capability of the
aircraft or the ability of the flightcrew to respond to an adverse
operating condition, must be designed and installed such that the
system recovers normal operation of that function in a timely manner
after the aircraft is exposed to lightning.
AM1.2520 High-Intensity Radiated Fields (HIRF) Protection
(a) Each electrical or electronic system that performs a function,
the failure of which would prevent the continued safe flight and
landing of the aircraft, must be designed and installed such that--
(1) The function at the aircraft level is not adversely affected
during and after the time the aircraft is exposed to the HIRF
environment; and
(2) The system recovers normal operation of that function in a
timely manner after the aircraft is exposed to the HIRF environment,
unless the system's recovery conflicts with other operational or
functional requirements of the system.
(b) For aircraft approved for IFR operations, each electrical and
electronic system that performs a function, the failure of which would
reduce the capability of the aircraft or the ability of the flightcrew
to respond to an adverse operating condition, must be designed and
installed such that the system recovers normal operation of that
function in a timely manner after the aircraft is exposed to the HIRF
environment.
Sec. 23.2525 System Power Generation, Storage, and Distribution
(a) through (c) [Applicable to Model M001]
Sec. 23.2530 External and Cockpit Lighting
(a) through (d) [Applicable to Model M001]
(e) [Not applicable to Model M001]
Sec. 23.2535 Safety Equipment
[Applicable to Model M001]
Sec. 23.2545 Pressurized Systems Elements
[Applicable to Model M001]
Sec. 23.2550 Equipment Containing High-Energy Rotors
[Applicable to Model M001]
Subpart G--Flightcrew Interface and Other Information
AM1.2600 Flightcrew Interface
(a) The pilot compartment, its equipment, and its arrangement to
include pilot view, must allow each pilot to perform their duties for
all sources of lift and phases of flight and perform any maneuvers
within the approved flight envelope of the aircraft, without excessive
concentration, skill, alertness, or fatigue.
(b) The applicant must install flight, navigation, surveillance,
and powerplant controls and displays, as needed, so qualified
flightcrew can monitor and perform defined tasks associated with the
intended functions of systems and equipment, without excessive
concentration, skill, alertness, or fatigue. The system and equipment
design must minimize flightcrew errors, which could result in
additional hazards.
Sec. 23.2605 Installation and Operation
(a) through (c) [Applicable to Model M001]
Sec. 23.2610 Instrument Markings, Control Markings, and Placards
(a) through (c) [Applicable to Model M001]
AM1.2615 Flight, Navigation, and Powerplant Instruments
(a) Installed systems must provide the flightcrew member who sets
or monitors parameters for the flight, navigation, and powerplant, the
information necessary to do so during each source of lift and phase of
flight. This information must--
(1) Be presented in a manner that the crewmember can monitor the
parameter and determine trends, as needed, to operate the aircraft; and
(2) Include limitations, unless the limitations cannot be exceeded
in all intended operations.
(b) Indication systems that integrate the display of flight or
powerplant parameters to operate the aircraft, or are required by the
operating rules of title 14, chapter I, must--
(1) Not inhibit the primary display of flight or powerplant
parameters needed by any flightcrew member in any normal mode of
operation; and
(2) In combination with other systems, be designed and installed so
information essential for continued safe flight and landing will be
available to the flightcrew in a timely manner after any single failure
or probable combination of failures.
AM1.2620 Aircraft Flight Manual
The applicant must provide an Aircraft Flight Manual that must be
delivered with each aircraft.
(a) The Aircraft Flight Manual must contain the following
information--
(1) Aircraft operating limitations;
(2) Aircraft operating procedures;
(3) Performance information;
(4) Loading information; and
(5) Other information that is necessary for safe operation because
of design, operating, or handling characteristics.
(b) The portions of the Aircraft Flight Manual containing the
information specified in paragraphs (a)(1) through (a)(4) of this
section must be approved by the FAA in a manner specified by the
Administrator.
Subpart H--Electric Engine Requirements
Sec. 33.5 Instruction Manual for Installing and Operating the Engine
(a) through (c) [Applicable to Model M001]
Sec. 33.7 Engine Ratings and Operating Limitations
(a) [Applicable to Model M001]
(b) through (d) [Not applicable to Model M001]
AM1.2702 Engine Ratings and Operating Limits
Ratings and operating limits must be established and included in
the type certificate data sheet based on:
(a) Shaft power, torque, rotational speed, and temperature for:
(1) Rated takeoff power;
(2) Rated maximum continuous power; and
(3) Rated maximum temporary power and associated time limit.
(b) Duty cycle and the rating at that duty cycle. The duty cycle
must be declared in the type certificate data sheet.
(c) Cooling fluid grade or specification.
(d) Power-supply requirements.
(e) Any other ratings or limitations that are necessary for the
safe operation of the engine.
[[Page 45972]]
Sec. 33.8 Selection of Engine Power and Thrust Ratings
(a) through (b) [Applicable to Model M001]
Sec. 33.15 Materials
(a) through (b) [Applicable to Model M001]
Sec. 33.17 Fire Protection
(a) [Not applicable to Model M001]
(b) through (g) [Applicable to Model M001]
AM1.2704 Fire Protection
(a) The design and construction of the engine and the materials
used must minimize the probability of the occurrence and spread of fire
during normal operation and failure conditions and must minimize the
effect of such a fire.
(b) High-voltage electrical wiring interconnect systems must be
protected against arc faults that can lead to hazardous engine effects
as defined in AM1.2717(d)(2). Non-protected electrical wiring
interconnects must be analyzed to show that arc faults do not cause a
hazardous engine effect.
AM1.2705 Durability
The engine design and construction must minimize the development of
an unsafe condition of the engine between maintenance intervals,
overhaul periods, or mandatory actions described in the applicable ICA.
Sec. 33.21 Engine Cooling
[Applicable to Model M001]
AM1.2706 Engine Cooling
If cooling is required to satisfy the safety analysis as described
in AM1.2717, the cooling-system monitoring features and usage must be
documented in the engine installation manual.
Sec. 33.23 Engine Mounting Attachments and Structure
(a) through (b) [Applicable to Model M001]
Sec. 33.25 Accessory Attachments
[Applicable to Model M001]
AM1.2709 Overspeed
(a) A rotor overspeed must not result in a burst, rotor growth, or
damage that results in a hazardous engine effect, as defined in
AM1.2717(d)(2). Compliance with this paragraph must be shown by test,
validated analysis, or a combination of both. Applicable assumed rotor
speeds must be declared and justified.
(b) Rotors must possess sufficient strength with a margin to burst
above approved operating conditions and above failure conditions
leading to rotor overspeed. The margin to burst must be shown by test,
validated analysis, or a combination thereof.
(c) The engine must not exceed the rotor-speed operational
limitations that could affect rotor structural integrity.
Sec. 33.28 Engine Control Systems
(b)(1)(i), (b)(1)(iii), and (b)(1)(iv) [Applicable to Model M001]
(a), (b)(1)(ii), and (b)(2) through (m) [Not applicable to Model
M001]
AM1.2710 Engine Control Systems
(a) Applicability.
These requirements apply to any system or device that is part of
the engine type design that controls, limits, monitors, or protects
engine operation and is necessary for the continued airworthiness of
the engine.
(b) Engine control.
The engine control system must ensure the engine does not
experience any unacceptable operating characteristics or exceed its
operating limits, including in failure conditions where the fault or
failure results in a change from one control mode to another, from one
channel to another, or from the primary system to the back-up system,
if applicable.
(c) Design assurance.
The software and complex electronic hardware, including
programmable logic devices, must be--
(1) Designed and developed using a structured and systematic
approach that provides a level of assurance for the logic commensurate
with the hazard associated with the failure or malfunction of the
systems in which the devices are located; and
(2) Substantiated by a verification methodology acceptable to the
Administrator.
(d) Validation.
All functional aspects of the control system must be substantiated
by test, analysis, or a combination thereof, to show that the engine
control system performs the intended functions throughout the declared
operational envelope.
(e) Environmental limits.
Environmental limits that cannot be adequately substantiated by
endurance demonstration, validated analysis, or a combination thereof
must be demonstrated by the system and component tests in AM1.2727.
(f) Engine control system failures.
The engine control system must--
(1) Have a maximum rate of Loss of Power Control (LOPC) that is
suitable for the intended aircraft application. The estimated LOPC rate
must be specified in the engine installation manual;
(2) When in the full-up configuration, be single fault tolerant, as
determined by the Administrator, for electrical, electrically
detectable, and electronic failures involving LOPC events;
(3) Not have any single failure that results in hazardous engine
effects as defined in AM1.2717(d)(2); and
(4) Ensure failures or malfunctions that lead to local events in
the aircraft do not result in hazardous engine effects as defined in
AM1.2717(d)(2) due to engine control system failures or malfunctions.
(g) System safety assessment.
The applicant must perform a system safety assessment. This
assessment must identify faults or failures that affect normal
operation, together with the predicted frequency of occurrence of these
faults or failures. The intended aircraft application must be taken
into account to ensure the assessment of the engine control system
safety is valid.
(h) Protection systems.
The engine control devices and systems' design and function,
together with engine instruments, operating instructions, and
maintenance instructions, must ensure that engine operating limits that
can lead to a hazard will not be exceeded in-service.
(i) Aircraft-supplied data.
Any single failure leading to loss, interruption, or corruption of
aircraft-supplied data (other than power command signals from the
aircraft), or aircraft-supplied data shared between engine systems
within a single engine or between fully independent engine systems,
must--
(1) Not result in a hazardous engine effect, as defined in
AM1.2717(d)(2), for any engine installed on the aircraft; and
(2) Be able to be detected and accommodated by the control system.
(j) Engine control system electrical power.
(1) The engine control system must be designed such that the loss,
malfunction, or interruption of the control system electrical power
source will not result in a hazardous engine effect, as defined in
AM1.2717(d)(2), the unacceptable transmission of erroneous data, or
continued engine operation in the absence of the control function. The
engine control system must be capable of resuming normal operation when
aircraft-supplied power returns to within the declared limits.
(2) The applicant must identify and declare, in the engine
installation manual, the characteristics of any electrical power
supplied from the aircraft to the engine control system, including
transient and steady-state
[[Page 45973]]
voltage limits, and any other characteristics necessary for safe
operation of the engine.
Sec. 33.29 Instrument Connection
(a), (e), and (g) [Applicable to Model M001]
(b) through (d), (f), and (h) [Not applicable to the Model M001]
AM1.2711 Instrument Connection
(a) In addition, as part of the system safety assessment of
AM1.2710(g) and AM1.2733(h), the applicant must assess the possibility
and subsequent effect of incorrect fit of instruments, sensors, or
connectors. Where practicable, the applicant must take design
precautions to prevent incorrect configuration of the system.
(b) The applicant must provide instrumentation enabling the
flightcrew to monitor the functioning of the engine cooling system
unless evidence shows that:
(1) Other existing instrumentation provides adequate warning of
failure or impending failure;
(2) Failure of the cooling system would not lead to hazardous
engine effects, as defined in AM1.2717(d)(2), before detection; or
(3) The probability of failure of the cooling system is extremely
remote.
AM1.2712 Stress Analysis
(a) A mechanical and thermal stress analysis, as well as an
analysis of the stress caused by electromagnetic forces, must show a
sufficient design margin to prevent unacceptable operating
characteristics and hazardous engine effects as defined in
AM1.2717(d)(2).
(b) Maximum stresses in the engine must be determined by test,
validated analysis, or a combination thereof, and must be shown not to
exceed minimum material properties.
Sec. 33.70 Engine Life Limited Parts
Introductory paragraph [Not applicable to Model M001]
(a) through (c) [Applicable to Model M001]
AM1.2713 Critical and Life-Limited Parts
(a) The applicant must show, by a safety analysis or means
acceptable to the Administrator, whether rotating or moving components,
bearings, shafts, static parts, and non-redundant mount components
should be classified, designed, manufactured, and managed throughout
their service life as critical or life-limited parts.
(1) Critical part means a part that must meet prescribed integrity
specifications to avoid its primary failure, which is likely to result
in a hazardous engine effect as defined in AM1.2717(d)(2).
(2) Life-limited parts may include but are not limited to a rotor
and major structural static part, the failure of which can result in a
hazardous engine effect, as defined in AM1.2717(d)(2), due to low-cycle
fatigue.
(b) In establishing the integrity of each critical part or life-
limited part, the applicant must provide to the Administrator the
following three plans for approval: an engineering plan, a
manufacturing plan, and a service-management plan, as defined in Sec.
33.70.
AM1.2714 Lubrication System
(a) The lubrication system must be designed and constructed to
function properly between scheduled maintenance intervals in all flight
attitudes and atmospheric conditions in which the engine is expected to
operate.
(b) The lubrication system must be designed to prevent
contamination of the engine bearings and lubrication system components.
(c) The applicant must demonstrate by test, validated analysis, or
a combination thereof, the unique lubrication attributes and functional
capability of paragraphs (a) and (b) of this section.
AM1.2715 Power Response
The design and construction of the engine, including its control
system, must enable an increase--
(a) From the minimum power setting to the highest rated power
without detrimental engine effects;
(b) From the minimum obtainable power while in flight, and while on
the ground, to the highest rated power within a time interval
determined to be appropriate for the intended aircraft application; and
(c) From the minimum torque to the highest rated torque without
detrimental engine effects in the intended aircraft application.
AM1.2716 Continued Rotation
If the design allows any of the engine main rotating systems to
continue to rotate after the engine is shut down while in-flight, this
continued rotation must not result in hazardous engine effects, as
specified in AM1.2717(d)(2).
Sec. 33.75 Safety Analysis
(a)(1) through (a)(2), (d), (e), and (g)(2) [Applicable to Model
M001]
(a)(3) through (c), (f), (g)(1), and (g)(3) [Not applicable to
Model M001]
AM1.2717 Safety Analysis
(a) The applicant must comply with Sec. 33.75(a)(1) and (2) using
the failure definitions in paragraph (d) of this section.
(b) The primary failure of certain single elements cannot be
sensibly estimated in numerical terms. If the failure of such elements
is likely to result in hazardous engine effects as defined in paragraph
(d)(2) of this section, then the applicant may show compliance by
reliance on the prescribed integrity requirements such as Sec. 33.15,
AM1.2709, AM1.2713, or combinations thereof, as applicable. The failure
of such elements and associated prescribed integrity requirements must
be stated in the safety analysis.
(c) The applicant must comply with Sec. 33.75(d) using the failure
definitions in paragraph (d) of this section, Sec. 33.75(e)(1) using
the ICA in AM1.1529 Appendix 1, and with Sec. 33.75(e)(4) using the
failure definitions in paragraph (d) of this section.
(d) Unless otherwise approved by the Administrator, the following
definitions apply to the engine effects when showing compliance with
these airworthiness criteria:
(1) A minor engine effect does not prohibit the engine from
performing its intended functions in a manner consistent with Sec.
33.28(b)(1)(i), (b)(1)(iii), and (b)(1)(iv), and the engine complies
with the operability requirements such as AM1.2715, AM1.2725, and
AM1.2731, as appropriate.
(2) The engine effects in Sec. 33.75(g)(2) are hazardous engine
effects, as are:
(i) Electrocution of the crew, passengers, operators, maintainers,
or others; and
(ii) Blockage of cooling systems that could cause the engine
effects described in Sec. 33.75(g)(2) and paragraph (d)(2)(i) of this
section.
(3) Any other engine effect is a major engine effect.
(e) The intended aircraft application must be taken into account to
assure that the analysis of the engine system safety is valid.
AM1.2718 Ingestion
(a) Rain, ice, and hail ingestion must not result in an abnormal
operation such as shutdown, power loss, erratic operation, or power
oscillations throughout the engine operating range.
(b) Ingestion from other likely sources (birds, induction system
ice, foreign objects--ice slabs) must not result in hazardous engine
effects, as defined in AM1.2717(d)(2), or unacceptable power loss.
(c) If the design of the engine relies on features, attachments, or
systems that the installer may supply, for the prevention of
unacceptable power loss
[[Page 45974]]
or hazardous engine effects as defined in AM1.2717(d)(2) following
potential ingestion, then the features, attachments, or systems must be
documented in the engine installation manual.
(d) Ingestion sources described in paragraph (b) of this section
that are not evaluated must be declared in the engine installation
manual.
AM1.2719 Liquid and Gas Systems
(a) Each system used for lubrication or cooling of engine
components must be designed and constructed to function properly in all
flight attitudes and atmospheric conditions in which the engine is
expected to operate.
(b) If a system used for lubrication or cooling of engine
components is not self-contained, the interfaces to that system must be
defined in the engine installation manual.
(c) The applicant must establish by test, validated analysis, or a
combination of both, that all static parts subject to significant
pressure loads will not:
(1) Exhibit permanent distortion beyond serviceable limits or
exhibit leakage that could create a hazardous condition when subjected
to normal and maximum working pressure with margin.
(2) Exhibit fracture or burst when subjected to the greater of
maximum possible pressures with margin.
(d) Compliance with paragraph (c) of this section must take into
account:
(1) The operating temperature of the part;
(2) Any other significant static loads in addition to pressure
loads;
(3) Minimum properties representative of both the material and the
processes used in the construction of the part; and
(4) Any adverse physical geometry conditions allowed by the type
design, such as minimum material and minimum radii.
(e) Approved coolants and lubricants must be listed in the engine
installation manual.
AM1.2720 Vibration Demonstration
(a) The engine must be designed and constructed to function
throughout its normal operating range of rotor speeds and engine output
power, including defined exceedances, without inducing excessive stress
in any of the engine parts because of vibration and without imparting
excessive vibration forces to the aircraft structure.
(b) Each engine design must undergo a vibration survey to establish
that the vibration characteristics of those components that may be
subject to induced vibration are acceptable throughout the approved
flight envelope and engine operating range for the specific
installation configuration. The possible sources of the induced
vibration that the survey must assess are mechanical, aerodynamic,
acoustical, internally induced electromagnetic, installation induced
effects that can affect the engine vibration characteristics, and
likely environmental effects. This survey must be shown by test,
validated analysis, or a combination thereof.
AM1.2721 Overtorque
When approval is sought for a transient maximum engine overtorque,
the applicant must demonstrate by test, validated analysis, or a
combination thereof, that the engine can continue operation after
operating at the maximum engine overtorque condition without
maintenance action. Upon conclusion of overtorque tests conducted to
show compliance with this subpart, or any other tests that are
conducted in combination with the overtorque test, each engine part or
individual groups of components must meet the requirements of AM1.2729.
AM1.2722 Calibration Assurance
Each engine must be subjected to calibration tests to establish its
power characteristics and the conditions both before and after the
endurance and durability demonstrations specified in AM1.2723 and
AM1.2726.
AM1.2723 Endurance Demonstration
(a) The applicant must subject the engine to an endurance
demonstration, acceptable to the Administrator, to demonstrate the
engine's limit capabilities.
(b) The endurance demonstration must include increases and
decreases of the engine's power settings, energy regeneration, and
dwellings at the power settings or energy regeneration for sufficient
durations that produce the extreme physical conditions the engine
experiences at rated performance levels, operational limits, and at any
other conditions or power settings that are required to verify the
limit capabilities of the engine.
AM1.2724 Temperature Limit
The engine design must demonstrate its capability to endure
operation at its temperature limits plus an acceptable margin. The
applicant must quantify and justify the margin to the Administrator.
The demonstration must be repeated for all declared duty cycles and
ratings, and operating environments, that would impact temperature
limits.
AM1.2725 Operation Demonstration
The engine design must demonstrate safe operating characteristics,
including but not limited to power cycling, starting, acceleration, and
overspeeding throughout its declared flight envelope and operating
range. The declared engine operational characteristics must account for
installation loads and effects.
AM1.2726 Durability Demonstration
The engine must be subjected to a durability demonstration to show
that each part of the engine has been designed and constructed to
minimize any unsafe condition of the system between overhaul periods or
between engine replacement intervals if the overhaul is not defined.
This test must simulate the conditions in which the engine is expected
to operate in service, including typical start-stop cycles, to
establish when the initial maintenance is required.
AM1.2727 System and Component Tests
The applicant must show that systems and components that cannot be
adequately substantiated in accordance with the endurance demonstration
or other demonstrations will perform their intended functions in all
declared environmental and operating conditions.
AM1.2728 Rotor Locking Demonstration
If shaft rotation is prevented by locking the rotor(s), the engine
must demonstrate:
(a) Reliable rotor locking performance;
(b) Reliable unlocking performance; and
(c) That no hazardous engine effects, as specified in
AM1.2717(d)(2), will occur.
AM1.2729 Teardown Inspection
(a) Teardown evaluation.
(1) After the endurance and durability demonstrations have been
completed, the-engine must be completely disassembled. Each engine
component and lubricant must be eligible for continued operation in
accordance with the information submitted for showing compliance with
AM1.1529.
(2) Each engine component having an adjustment setting and a
functioning characteristic that can be established independent of
installation on or in the engine must retain each setting and
functioning characteristic within the established and recorded limits
at the
[[Page 45975]]
beginning of the endurance and durability demonstrations.
(b) Non-Teardown evaluation.
If a teardown cannot be performed for all engine components in a
non-destructive manner, then the inspection or replacement intervals
for these components and lubricants must be established based on the
endurance and durability demonstrations and documented in the ICA in
accordance with AM1.1529.
AM1.2730 Containment
The engine must be designed and constructed to protect against
likely hazards from rotating components as follows--
(a) The design of the case surrounding rotating components must
provide for the containment of the rotating components in the event of
failure, unless the applicant shows that the margin to rotor burst
precludes the possibility of a rotor burst.
(b) If the margin to burst shows the case must have containment
features in the event of failure, the case must provide for the
containment of the failed rotating components. The applicant must
define by test, validated analysis, or a combination thereof, and
document in the engine installation manual, the energy level,
trajectory, and size of fragments released from damage caused by the
main rotor failure, and that pass forward or aft of the surrounding
case.
AM1.2731 Operation With a Variable-Pitch Propeller
The applicant must conduct functional demonstrations including
feathering, negative torque, negative thrust, and reverse thrust
operations, as applicable, with a representative propeller. These
demonstrations may be conducted in a manner acceptable to the
Administrator as part of the endurance, durability, and operation
demonstrations.
AM1.2732 General Conduct of Tests
(a) Maintenance of the engine may be made during the tests in
accordance with the service and maintenance instructions submitted in
compliance with AM1.1529, ICA.
(b) The applicant must subject the engine or its parts to
maintenance and additional tests that the Administrator finds necessary
if--
(1) The frequency of the service is excessive;
(2) The number of stops due to engine malfunction is excessive;
(3) Major repairs are needed; or
(4) Replacement of a part is found necessary during the tests or
due to the teardown inspection findings.
(c) Upon completion of all demonstrations and testing specified in
these airworthiness criteria, the engine and its components must be--
(1) Within serviceable limits;
(2) Safe for continued operation; and
(3) Capable of operating at declared ratings while remaining within
limits.
AM1.2733 Engine Electrical Systems
(a) Applicability.
Any system or device that provides, uses, conditions, or
distributes electrical power, and is part of the engine type design,
must provide for the continued airworthiness of the engine and maintain
electric engine ratings.
(b) Electrical systems.
The electrical system must ensure the safe generation and
transmission of power, electrical load shedding, and that the engine
does not experience any unacceptable operating characteristics or
exceed its operating limits.
(c) Electrical-power distribution.
(1) The engine electrical-power distribution system must be
designed to provide the safe transfer of electrical energy throughout
the electrical power plant. The system must be designed to provide
electrical power so that the loss, malfunction, or interruption of the
electrical power source will not result in a hazardous engine effect,
as defined in AM1.2717(d)(2).
(2) The system must be designed and maintained to withstand normal
and abnormal conditions during all ground and flight operations.
(3) The system must provide mechanical or automatic means to
mitigate a faulted electrical-energy generation or storage device from
leading to hazardous engine effects, as defined in AM1.2717(d)(2), or
detrimental effects in the intended aircraft application.
(d) Protection systems.
The engine electrical system must be designed such that the loss,
malfunction, interruption of the electrical power source, or power
conditions that exceed design limits will not result in hazardous
engine effects, as defined in AM1.2717(d)(2), or detrimental effects in
the intended aircraft application.
(e) Electrical Power Characteristics.
The applicant must identify and declare, in the engine installation
manual, the characteristics of any electrical power--
(1) Supplied from the aircraft to the engine electrical system, for
starting and operating the engine, including transient and steady-state
voltage limits, or
(2) Supplied from the engine to the aircraft via energy
regeneration, and any other characteristics necessary for safe
operation of the engine.
(f) Environmental limits.
Environmental limits that cannot be adequately substantiated by
endurance demonstration, validated analysis, or a combination thereof
must be demonstrated by the system and component tests in AM1.2727.
(g) Electrical-system failures.
The engine electrical system must--
(1) Have a maximum rate of Loss of Power Control (LOPC) that is
suitable for the intended aircraft application;
(2) When in the full-up configuration, be single fault tolerant, as
determined by the Administrator, for electrical, electrically
detectable, and electronic failures involving LOPC events;
(3) Not have any single failure that results in hazardous engine
effects as defined in AM1.2717(d)(2); and
(4) Not have any likely failure or malfunction that leads to local
events in the intended aircraft application.
(h) System safety assessment.
The applicant must perform a system safety assessment. This
assessment must identify faults or failures that affect normal
operation, together with the predicted frequency of occurrence of these
faults or failures. The intended aircraft application must be taken
into account to assure the assessment of the engine system safety is
valid.
Subpart I--Propeller Requirements
AM1.2805 Propeller Ratings and Operating Limitations
Propeller ratings and operating limitations must be established by
the applicant and approved by the Administrator, including ratings and
limitations based on the operating conditions and information specified
in this subpart, as applicable, and any other information found
necessary for safe operation of the propeller.
Sec. 35.7 Features and Characteristics
(a) through (b) [Applicable to Model M001]
AM1.2815 Safety Analysis
(a) The applicant must:
(1) Analyze the propeller system to assess the likely consequences
of all failures that can reasonably be expected to occur. This analysis
will take into account, if applicable:
(i) The propeller system when installed on the aircraft. When the
analysis depends on representative components, assumed interfaces, or
assumed installed conditions, the assumptions must be stated in the
analysis.
(ii) Consequential secondary failures and dormant failures.
[[Page 45976]]
(iii) Multiple failures referred to in paragraph (d) of this
section, or that result in the hazardous propeller effects defined in
paragraph (g)(1) of this section.
(2) Summarize those failures that could result in major propeller
effects or hazardous propeller effects defined in paragraph (g) of this
section, and estimate the probability of occurrence of those effects.
(3) Show that hazardous propeller effects are not predicted to
occur at a rate in excess of that defined as extremely remote
(probability of 10-7 or less per propeller flight hour).
Because the estimated probability for individual failures may be
insufficiently precise to enable the applicant to assess the total rate
for hazardous propeller effects, compliance may be shown by
demonstrating that the probability of a hazardous propeller effect
arising from an individual failure can be predicted to be not greater
than 10-8 per propeller flight hour. In dealing with
probabilities of this low order of magnitude, absolute proof is not
possible, and reliance must be placed on engineering judgment and
previous experience, combined with sound design and test philosophies.
(b) If significant doubt exists as to the effects of failures or
likely combination of failures, the Administrator may require
assumptions used in the analysis to be verified by test.
(c) The primary failures of certain single propeller elements (for
example, blades) cannot be sensibly estimated in numerical terms. If
the failure of such elements is likely to result in hazardous propeller
effects, those elements must be identified as propeller critical parts.
For propeller critical parts, the applicant must meet the prescribed
integrity specifications of AM1.2816. These instances must be stated in
the safety analysis.
(d) If reliance is placed on a safety system to prevent a failure
progressing to hazardous propeller effects, the possibility of a safety
system failure, in combination with a basic propeller failure, must be
included in the analysis. Such a safety system may include safety
devices, instrumentation, early warning devices, maintenance checks,
and other similar equipment or procedures.
(e) If the safety analysis depends on one or more of the following
items, those items must be identified in the analysis and appropriately
substantiated.
(1) Maintenance actions being carried out at stated intervals. This
includes verifying that items that could fail in a latent manner are
functioning properly. When necessary to prevent hazardous propeller
effects, these maintenance actions and intervals must be published in
the ICA required under AM1.1529. Additionally, if errors in maintenance
of the propeller system could lead to hazardous propeller effects, the
appropriate maintenance procedures must be included in the relevant
propeller manuals.
(2) Verification of the satisfactory functioning of safety or other
devices at pre-flight or other stated periods. The details of this
satisfactory functioning must be published in the appropriate manual.
(3) The provision of specific instrumentation not otherwise
required. Such instrumentation must be published in the appropriate
documentation.
(4) A fatigue assessment.
(f) If applicable, the safety analysis must include, but not be
limited to, assessment of indicating equipment, manual and automatic
controls, governors and propeller-control systems, synchrophasers,
synchronizers, and propeller thrust reversal systems.
(g) Unless otherwise approved by the Administrator and stated in
the safety analysis, the following failure definitions apply to
compliance with these airworthiness criteria.
(1) The following are regarded as hazardous propeller effects:
(i) The development of excessive drag.
(ii) A significant thrust in the opposite direction to that
commanded by the pilot.
(iii) The release of the propeller or any major portion of the
propeller.
(iv) A failure that results in excessive unbalance.
(2) The following are regarded as major propeller effects for
variable-pitch propellers:
(i) An inability to feather the propeller for feathering
propellers.
(ii) An inability to change propeller pitch when commanded.
(iii) A significant uncommanded change in pitch.
(iv) A significant uncontrollable torque or speed fluctuation.
AM1.281 Propeller Critical Parts
The integrity of each propeller critical part identified by the
safety analysis required by AM1.2815 must be established by:
(a) A defined engineering process for ensuring the integrity of the
propeller critical part throughout its service life,
(b) A defined manufacturing process that identifies the
requirements to consistently produce the propeller critical part as
required by the engineering process, and
(c) A defined service-management process that identifies the
continued airworthiness requirements of the propeller critical part as
required by the engineering process.
Sec. 35.17 Materials and Manufacturing Methods
(a) through (c) [Applicable to Model M001]
Sec. 35.19 Durability
[Applicable to Model M001]
AM1.2821 Variable- and Reversible-Pitch Propellers
(a) No single failure or malfunction in the propeller system will
result in unintended travel of the propeller blades to a position below
the in-flight low-pitch position. The extent of any intended travel
below the in-flight low-pitch position must be documented by the
applicant in the appropriate manuals. Failure of structural elements
need not be considered if the occurrence of such a failure is shown to
be extremely remote under AM1.2815.
(b) For propellers incorporating a method to select blade pitch
below the in-flight low-pitch position, provisions must be made to
sense and indicate to the flightcrew that the propeller blades are
below that position by an amount defined in the installation
instructions. The method for sensing and indicating the propeller blade
pitch position must be such that its failure does not affect the
control of the propeller.
Sec. 35.22 Feathering Propellers
(a) through (c) [Applicable to Model M001]
AM1.2823 Propeller Control System
The requirements of this section apply to any system or component
that controls, limits, or monitors propeller functions.
(a) The propeller control system must be designed, constructed and
validated to show that:
(1) The propeller control system, operating in normal and
alternative operating modes and in transition between operating modes,
performs the functions defined by the applicant throughout the declared
operating conditions and approved flight envelope.
(2) The propeller control system functionality is not adversely
affected by the declared environmental conditions, including
temperature, electromagnetic interference (EMI), high intensity
radiated fields (HIRF), and lightning. The environmental limits to
which the system has been satisfactorily validated must be documented
in the appropriate propeller manuals.
(3) A method is provided to indicate that an operating mode change
has
[[Page 45977]]
occurred if flightcrew action is required. In such an event, operating
instructions must be provided in the appropriate manuals.
(b) The propeller control system must be designed and constructed
so that, in addition to compliance with AM1.2815:
(1) No single failure results in a hazardous propeller effect;
(2) Local events in the intended aircraft installation will not
result in hazardous propeller effects;
(3) The loss of normal propeller pitch control does not cause a
hazardous propeller effect under the intended operating conditions; and
(4) The failure or corruption of data or signals shared across
propellers does not cause a hazardous propeller effect.
(c) Electronic propeller-control-system embedded software must be
designed and implemented by a method approved by the Administrator that
is consistent with the criticality of the performed functions and that
minimizes the existence of software errors.
(d) The propeller control system must be designed and constructed
so that the failure or corruption of aircraft-supplied data does not
result in hazardous propeller effects.
(e) The propeller control system must be designed and constructed
so that the loss, interruption, or abnormal characteristic of aircraft-
supplied electrical power does not result in hazardous propeller
effects. The power quality requirements must be described in the
appropriate manuals.
Sec. 35.24 Strength
[Applicable to Model M001]
Sec. 35.33 General
(a) through (c) [Applicable to Model M001]
Sec. 35.34 Inspections, Adjustments, and Repairs
(a) through (b) [Applicable to Model M001]
Sec. 35.35 Centrifugal Load Tests
(a) through (c) [Applicable to Model M001]
Sec. 35.36 Bird Impact
[Applicable to Model M001]
Sec. 35.37 Fatigue Limits and Evaluation
(a) through (c)(1) [Applicable to Model M001, except replace the
reference to Sec. 35.15 with AM1.2815, and the reference to ``Sec.
23.2400(c) or Sec. 25.907'' with AM1.2400(c)]
(c)(2) [Not applicable to Model M001]
Sec. 35.38 Lightning Strike
[Applicable to Model M001]
Sec. 35.39 Endurance Test
(a) through (c) [Applicable to Model M001, except replace the
reference to ``part 33'' with ``these airworthiness criteria'']
AM1.2840 Functional Test
The variable-pitch propeller system must be subjected to the
applicable functional tests of this section. The same propeller system
used in the endurance test of Sec. 35.39 must be used in the
functional tests and must be driven by a representative engine on a
test stand or on the aircraft. The propeller must complete these tests
without evidence of failure or malfunction. This test may be combined
with the endurance test for accumulation of cycles.
(a) Governing and reversible-pitch propellers. Fifteen hundred
complete cycles must be made across the range of forward pitch and
rotational speed. In addition, 200 complete cycles of control must be
made from lowest normal pitch to maximum reverse pitch. During each
cycle, the propeller must run for 30 seconds at the maximum power and
rotational speed selected by the applicant for maximum reverse pitch.
(b) Feathering propellers. Fifty cycles of feather and unfeather
operation must be made.
(c) An analysis based on tests of propellers of similar design may
be used in place of the tests of this section.
Sec. 35.41 Overspeed and Overtorque
(a) through (b) [Applicable to Model M001]
Sec. 35.42 Components of the Propeller Control System
[Applicable to Model M001]
Appendix A to Part 23--Instructions for Continued Airworthiness
A23.1 through A23.3(g) and A23.4 [Applicable to Model M001]
A23.3(h) [Not applicable to Model M001]
Appendix A1--Instructions for Continued Airworthiness (Electric Engine)
AAM1.2701 General
(a) This appendix specifies requirements for the preparation of
ICA for the engines as required by AM1.1529.
(b) The ICA for the engine must include the ICA for all engine
parts.
(c) The applicant must submit to the FAA a program to show how
the applicant's changes to the ICA will be distributed, if
applicable.
A33.2 Format
(a) through (b) [Applicable to Model M001]
A33.3 Content
(a) and (b) [Applicable to Model M001]
(c) [Not applicable to Model M001]
A33.4 Airworthiness Limitations Section
(a) [Applicable to Model M001]
(b) [Not applicable to Model M001]
Appendix A2--Instructions for Continued Airworthiness (Propellers)
AAM1.2801 General
(a) This appendix specifies requirements for the preparation of
ICA for the propellers as required by AM1.1529.
(b) The ICA for the propeller must include the ICA for all
propeller parts.
(c) The applicant must submit to the FAA a program to show how
changes to the ICA made by the applicant or by the manufacturers of
propeller parts will be distributed, if applicable.
A35.2 Format
(a) through (b) [Applicable to Model M001]
A35.3 Content
(a) through (b) [Applicable to Model M001]
A35.4 Airworthiness Limitations Section
[Applicable to Model M001]
Issued in Des Moines, WA, on May 14, 2024.
Caspar K. Wang,
Acting Manager, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service.
[FR Doc. 2024-11192 Filed 5-23-24; 8:45 am]
BILLING CODE 4910-13-P