[Federal Register Volume 86, Number 184 (Monday, September 27, 2021)]
[Rules and Regulations]
[Pages 53508-53534]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-19926]
[[Page 53507]]
Vol. 86
Monday,
No. 184
September 27, 2021
Part III
Department of Transportation
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Federal Aviation Administration
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14 CFR Part 33
Special Conditions: magniX USA, Inc., magni350 and magni650 Model
Engines; Electric Engine Airworthiness Standards; Final Rule
Federal Register / Vol. 86, No. 184 / Monday, September 27, 2021 /
Rules and Regulations
[[Page 53508]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 33
[Docket No. FAA-2020-0894; Special Conditions No. 33-022-SC]
Special Conditions: magniX USA, Inc., magni350 and magni650 Model
Engines; Electric Engine Airworthiness Standards
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the magniX USA, Inc.,
(magniX), magni350 and magni650 model engines, which operate using
electrical technology installed on the aircraft for use as an aircraft
engine. These engines have a novel or unusual design feature when
compared to the state of technology envisioned in the airworthiness
standards applicable to aircraft engines. This design feature is an
electric motor, controller, and high-voltage systems as the primary
source of propulsion for an aircraft. The applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
this design feature. These special conditions contain the additional
safety standards that the Administrator considers necessary to
establish a level of safety equivalent to that established by the
existing airworthiness standards.
DATES: Effective October 27, 2021.
FOR FURTHER INFORMATION CONTACT: Mark Bouyer, AIR-624, Propulsion and
Energy, Technical Innovation Policy Branch, Aircraft Certification
Service, 1200 District Avenue, Burlington, Massachusetts 01803;
telephone (781) 238-7755; [email protected].
SUPPLEMENTARY INFORMATION:
Background
On April 18, 2019,\1\ magniX applied for a type certificate for its
magni350 and magni650 model electric engines.\2\ The FAA has not
previously type certificated an engine that primarily uses electrical
technology for propulsion of the aircraft. Electric propulsion
technology is substantially different from the technology used in
previously certificated aircraft engines that operate using aviation
fuel; therefore, these engines introduce new safety concerns that need
to be addressed in the certification basis.
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\1\ The Notice of Proposed Special Conditions, published on
November 19, 2020 (85 FR 73644), inaccurately indicated June 4,
2019, as magniX's type certificate application date.
\2\ magniX submitted a comment which notified the FAA that the
magniX engine model numbers were changed from magni250 and magni500
to magni350 and magni650, respectively. The model number change does
not represent a change in the certification requirements of the
engine.
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As noted in the Notice of Proposed Special Conditions, the FAA used
technical criteria from ASTM F3338-18, Standard Specification for
Design of Electric Propulsion Units for General Aviation Aircraft,\3\
along with engine information from magniX and other information, to
develop these special conditions. These special conditions establish a
level of safety that is equivalent to the level of safety required by
title 14, Code of Federal Regulations (14 CFR) part 33.
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\3\ https://www.astm.org/DATABASE.CART/HISTORICAL/F3338-18.htm.
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Type Certification Basis
Under the provisions of 14 CFR 21.17(a)(1), generally, magniX must
show that magni350 and magni650 model engines meet the applicable
provisions of 14 CFR part 33 in effect on the date of application for a
type certificate.
If the Administrator finds that the applicable airworthiness
regulations (e.g., 14 CFR part 33) do not contain adequate or
appropriate safety standards for the magni350 and magni650 model
engines because of a novel or unusual design feature, special
conditions may be prescribed under the provisions of Sec. 21.16.
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other engine model that incorporates the same
novel or unusual design feature, these special conditions would also
apply to the other engine model under Sec. 21.101. The FAA issues
special conditions, as defined in 14 CFR 11.19, in accordance with
Sec. 11.38, and they become part of the type certification basis under
Sec. 21.17(a)(2).
Novel or Unusual Design Feature
The magni350 and magni650 model engines will incorporate the
following novel or unusual design feature:
An electric motor, controller, and high-voltage systems is used as
the primary source of propulsion for an aircraft.
Discussion
14 CFR Part 33 Developed for Aircraft Engines That Operate Using
Aviation Fuel
Aircraft engines make use of an energy source to drive mechanical
systems that provide propulsion for the aircraft. The turbine and
reciprocating aircraft engines certified under part 33 use aviation
fuel as an energy source. The technology that the FAA anticipated in
the development of 14 CFR part 33 converts oxygen and fuel to generate
energy through an internal combustion system, which generates heat and
mass flow of combustion products for turning shafts attached to
propulsion devices such as propellers and ducted fans. Part 33
regulations set forth standards for these engines and mitigate
potential hazards resulting from failures and malfunctions. The nature,
progression, and severity of engine failures are tied closely to the
technology that engine manufacturers use in designing and manufacturing
aircraft engines. These technologies involve chemical, thermal, and
mechanical systems. Therefore, the existing engine regulations in 14
CFR part 33 address certain chemical, thermal, and mechanically induced
failures specific to air and fuel combustion systems operating with
cyclically loaded high-speed, high-temperature, highly-stressed
components.
magniX's Electric Engines Are Novel or Unusual
The FAA's current airworthiness standards for aircraft engines, 14
CFR part 33, date back to 1964.\4\ The FAA based these airworthiness
standards on aircraft engines that operate using aviation fuel; such
engines have mechanical systems that provide propulsion for aircraft.
However, the magniX magni350 and magni650 model engines have a novel or
unusual design feature which uses an electrical energy source instead
of aviation fuel to drive the mechanical systems. The electric engine
is exposed to chemical, thermal, and mechanical operating conditions
that are unlike those observed in internal-combustion systems.
Therefore, 14 CFR part 33 does not contain adequate safety standards
for the magniX magni350 and magni650 model engines' novel or unusual
design feature.
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\4\ 29 FR 7452.
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The two models of electric engine that have been proposed by magniX
will use electrical power instead of air and fuel combustion to propel
the aircraft. These electric engines will be designed, manufactured,
and controlled differently than aircraft engines that operate using
aviation fuel. They will be built with an electric motor, controller,
and high-voltage systems that draw energy from electrical storage or
[[Page 53509]]
generating systems. The magniX motor, in both models, is a device that
converts electrical energy into mechanical energy by electric current
flowing through wire coils in the motor, producing a magnetic field
that interacts with magnets on the rotating shaft. The controller is a
system that consists of two main functional elements: the motor
controller and an electric power inverter to drive the motor.\5\ The
high-voltage system is a combination of wires and connectors that
couple the motor and the controller.
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\5\ Sometimes this entire system is referred to as an inverter.
Throughout this document, the controller and inverter will be
referred to as the controller.
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In addition, the technology required to produce these high-voltage
and high-current electronic components introduces potential hazards
that do not exist in aircraft engines that operate using aviation fuel.
For example, high-voltage transmission lines, electromagnetic fields,
magnetic materials, and high-speed electrical switches form the
electric engine's physical properties. However, this technology also
exposes the aircraft to potential failures that are not common to
aircraft engines that operate using aviation fuel, which could
adversely affect safety.
magniX's Electric Engines Require a Mix of 14 CFR Part 33 Standards and
Special Conditions
Although magniX's proposed electric engines incorporate a novel or
unusual design feature that the FAA did not envisage during the
development of its existing 14 CFR part 33 airworthiness standards,
these engines share some basic similarities, in configuration and
function, to engines that use the combustion of fuel and air, and
therefore they require similar provisions to prevent common hazards
(e.g., fire, uncontained high-energy debris, and loss of thrust
control). However, the primary failure concerns and the probability of
exposure to common hazards are different for the electric engines. This
probability creates a need to develop special conditions to ensure the
engine's safety and reliability.
14 CFR part 33 does not fully address aircraft engines like
magniX's, which use electrical technology as the primary means of
propelling the aircraft. This necessitates the development of special
conditions to provide adequate airworthiness standards for these
aircraft engines.
The requirements in 14 CFR part 33, subparts B through G, apply to
aircraft engines that operate using aviation fuel. Subpart B applies to
reciprocating and turbine aircraft engines. Subparts C and D apply to
reciprocating aircraft engines. Subparts E through G apply to turbine
aircraft engines. As such, subparts B through G do not adequately
address aircraft engines that operate using electrical technology. This
necessitates the development of special conditions to ensure a level of
safety commensurate with these subparts, as those regulatory
requirements do not contain adequate or appropriate safety standards
for aircraft engines that primarily use electrical technology to propel
the aircraft.
Discussion of Special Conditions and Comments
The FAA issued Notice of Proposed Special Conditions No. 33-19-01-
SC (the Notice) for these proposed engines. This document was published
in the Federal Register on November 19, 2020 (85 FR 73644). The FAA
received comments from eleven organizations and two individuals.
The organizations that commented were Wisk Aero (Wisk), Rolls-Royce
North America (Rolls-Royce), GE Aviation (GE), Ampaire Inc. (Ampaire),
Textron Aviation (Textron), Associacao Das Industrias Aeroespaciais Do
Brasil (AIAB), Safran Electrical & Power (Safran), Airbus Commercial
Aircraft (Airbus), magniX USA, Inc. (magniX), Transport Canada Civil
Aviation (TCCA), and European Union Aviation Safety Agency (EASA).
The following summarizes each special condition proposed by the
FAA; the pertinent comments, and the FAA's response, including whether
the FAA made any changes in these final special conditions.
Special Condition No. 1, Applicability
The FAA proposed that Special Condition no. 1 would require magniX
to comply with 14 CFR part 33, except for those airworthiness standards
specifically and explicitly applicable only to reciprocating and
turbine aircraft engines.
Comment Summary: TCCA commented that proposed Special Condition no.
1 could be read in different ways regarding which sections of 14 CFR
part 33 apply directly to electric engines and that applicants might
disagree when assessing the appropriate airworthiness requirements for
their engine designs. TCCA also suggested a manner in which to reformat
this special condition.
FAA Response: These special conditions are not intended for all
electric engine projects, only for the two models of engine proposed by
magniX. Addressing the 14 CFR, part 33 applicability portion of the
comment, the requirements in part 33, subpart B, are applicable to
reciprocating and turbine aircraft engines. Subparts C and D are
applicable to reciprocating aircraft engines. Subparts E through G are
applicable to turbine aircraft engines. As the magni350 and magni650
model engines are not reciprocating or turbine engines, subparts B
through G of part 33 are not applicable to these engines unless these
special conditions expressly require compliance, as set forth herein.
The FAA did not change the special condition as a result of this
comment.
Comment Summary: TCCA requested that Special Condition no. 1
include an additional requirement. TCCA asked that the FAA require the
applicant to specify, within the engine installation manual, the
electrical bonding for the installation of the engine and its control
system. TCCA explained that proper bonding is required to protect the
engine and the control system from the effects of lightning and
electrostatic electricity, noting that 14 CFR 33.5(a) does not
explicitly require electrical bonding instructions to be included in
the engine installation manual.
FAA Response: Special Condition no. 10(e) addresses environmental
limits for the magniX engines, which include electromagnetic
interference, high-intensity radiated fields, and lightning. The
assessments that verify environmental limits account for the effects of
electrical bonding. A special condition for electrical bonding is not
required to establish proper electrical bonding. Special Condition no.
1 mandates compliance with Sec. 33.5(a), which addresses all physical
and functional interfaces with the aircraft, including TCCA's
recommendation to specify electrical bonding details in the engine
installation instructions. The FAA made no changes to the special
condition as a result of this comment.
Comment Summary: Wisk stated the inclusion of the high voltage and
high current electrical system within the system covered by the engine
OEM introduces aspects of 14 CFR 23.2525 that have not typically been
addressed by engine OEMs before. Wisk added that consideration within
the proposed SC for these aspects would ensure a safer product during
the development, flight test, and service lifecycle. Wisk proposed the
FAA consider applying Sec. 23.2525(a) and (b), and possibly other
relevant regulations to the components between the controller and motor
in the engine system.
FAA Response: The requirements Wisk identifies in their comment
apply to system power generation, storage, and distribution. These
special conditions
[[Page 53510]]
apply only to the magniX engine designs, which do not include the power
systems addressed in 14 CFR 23.2525. These power systems are normally
approved as part of the airplane. Therefore, any other relevant part 23
airplane requirements would also be addressed during the airplane
certification program. The FAA did not change this special condition as
a result of this comment.
Comment Summary: Wisk acknowledged that the high voltage and
current electrical system is analogous to the traditional fuel system.
As such, omitting regulations that are equivalent to all, or parts of
14 CFR 33.67 from these special conditions may result in a loss of a
critical interface boundary, resulting in a lack of clear ownership
between the airframe and engine OEM. Wisk requested that the FAA
clarify within the proposed SC the analogous aspects of Sec. 33.67 for
the interface between the engine controller and the airframe electrical
system as it relates to voltage and current.
FAA Response: 14 CFR 33.67 includes requirements for features that
do not exist in the magniX engine electrical system. However, the
analogous aspects of Sec. 33.67 are included Special Condition no. 2,
which requires magniX to establish and declare ratings and operating
limits based on power-supply requirements for the engine. Therefore,
Special Condition no. 2 addresses Wisk's comment. The FAA did not
change this special condition as a result of this comment.
Special Condition No. 2, Engine Ratings and Operating Limits
The FAA proposed that Special Condition no. 2 would require magniX,
in addition to compliance with 14 CFR 33.7(a), to establish engine
operating limits related to the shaft horsepower, torque, speed, and
duty cycle(s). The duty cycle is an engine rating that declares a
performance capability for the load(s) that will be imposed on the
engine, including, if applicable, starting, no-load and rest, and de-
energized periods, including their durations or cycles and sequence in
time.
Comment Summary: Wisk recommended that the FAA expand the ratings
and operating limits required by Special Condition no. 2 to include
maximum temperature, maximum and minimum voltage, current, and power;
and, if applicable, coolant and/or lubrication temperatures & pressures
for safe operation.
FAA Response: It is not necessary to impose voltage and current
limits to ensure that these magniX engines achieve the same level of
safety intended by 14 CFR part 33. The FAA has changed final Special
Condition no. 2 to add temperature and power (power-supply)
requirements to the engine ratings and operating limits.
Comment Summary: Wisk stated that proposed Special Condition no.
2(a)(1) (Rated Maximum Continuous Power) should not have a time limit
as it is continuous. Wisk suggested deleting the word ``time'' from
proposed Special Condition no. 2(a).
FAA Response: The FAA agrees that the power at the ``Rated Maximum
Continuous Power'' rating is not time limited. The FAA has modified
final Special Condition no. 2 to remove the time constraint from the
rating.
Comment Summary: Wisk suggested that the FAA specify coolant and
lubrication temperatures and pressures for safe operation.
FAA Response: The FAA does not agree with Wisk's suggestion. A
special condition is not required for coolant and lubrication
(operating) temperatures. Special Condition nos. 6 (Engine cooling) and
14 (Lubrication system) address Wisk's suggestion. No changes were made
to this special condition as a result of Wisk's comment.
Comment Summary: Rolls-Royce commented that, by placing a duty
cycle on the engine's type certificate data sheet, proposed Special
Condition no. 2 would be overly prescriptive when compared to the FAA's
requirements for aircraft engines that operate using aviation fuel.
Rolls-Royce stated that Special Condition no. 2(b) should be removed,
and the FAA should require the applicant to define a duty cycle in the
Airworthiness Limitations Section of the Operating Manual.
FAA Response: The magni350 and magni650 electric engines have
different operating characteristics than conventional reciprocating or
turbine engines. The performance capability of electric engine designs
is defined, in part, by a duty cycle. Therefore the FAA did not change
this special condition as a result of this comment.
Comment Summary: GE recommended that the FAA modify Special
Condition no. 2 to require the applicant to list the engine's cooling
fluid as an engine operating limitation, similar to 14 CFR 33.7(b)(3),
which requires, for reciprocating engines, established ratings and
operating limitations related to oil grade or specification.
FAA Response: The FAA agrees with the comment and has modified
final Special Condition no. 2 to require a cooling fluid grade or
specification as an operating limit.
Comment Summary: Ampaire commented that the term ``power,'' as used
in proposed Special Condition no. 2, is not the most relevant metric
for electric machinery and power electronics. Ampaire stated that it
understood ``power,'' as used in that condition, to be the electrical
power output delivered by the magniX engine. Ampaire recommended that
the FAA change the requirement to specify current and voltage.
FAA Response: The FAA does not agree with the comment. As used in
Special Condition no. 2, ``power'' describes the mechanical shaft
horsepower supplied by the engine to propel the aircraft and not the
electrical power delivered by the engine. The FAA made no changes to
the special condition as a result of the comment.
Comment Summary: Ampaire asked that the FAA include more details
from ASTM F3338-18, such as those listed in sections 5.3.1-5.3.8, EPU
Operating Limitations and Ratings, in Special Condition no. 2.
FAA Response: The FAA does not agree with the comment. ASTM F3338-
18 contains technical criteria that the FAA used in developing these
special conditions. The airworthiness requirements for these engines
include paragraphs from the ASTM specification and from 14 CFR part 33.
The FAA made no changes to the special condition as a result of this
comment.
Comment Summary: Textron recommended that the FAA add engine
temperature to the ratings and operating limits mandated by Special
Condition no. 2.
FAA Response: The FAA agrees with the comment. The FAA has changed
final Special Condition no. 2 to add temperature to the engine ratings
and operating limits.
Comment Summary: Textron stated the term ``speed,'' as used in
Special Condition no. 2(a), could be misleading and mistaken for
aircraft speed or gearbox output-shaft speed. Textron stated the term
``speed'' should instead be ``RPM.''
FAA Response: The FAA does not agree with the comment. Engine speed
is typically measured in units that describe a rate of mechanical
rotation. In Special Condition no. 2, the word ``speed,'' used in the
context of ``rotational speed,'' applies to the output-shaft rotation
rate. The applicant can express engine speed using various units, so
the measurement unit of the engine shaft rotation does not need to be
prescribed in Special Condition no. 2. The FAA did not change the
special condition based on the comment.
[[Page 53511]]
Comment Summary: Textron recommended that the FAA add rated takeoff
power to the required engine ratings and operating limits in Special
Condition no. 2.
FAA Response: The FAA agrees and has added ``rated takeoff power''
to the engine ratings and operating limits in final Special Condition
no. 2.
Comment Summary: TCCA suggested that the engine ratings and
operating limits not be limited to those proposed in Special Condition
no. 2(a). TCCA recommended adding a statement that requires magniX to
include any other ratings or limitations that are necessary for the
safe operation of the engine.
FAA Response: The engine ratings and operating limits that Special
Condition no. 2 requires are based on existing aircraft engine
technologies. However, electric engine technology is new to aviation.
The FAA has modified Special Condition no. 2 to require additional
ratings if they are determined to be necessary for the safe operation
of the engine.
Comment Summary: TCCA asked why the FAA did not mandate that the
applicant comply with 14 CFR 33.7(d) within Special Condition no. 2.
Similarly, AIAB commented that Special Condition no. 2 should mandate
compliance with 14 CFR 33.7(d), since the electric motor can be
affected by the accuracy of the engine control system and
instrumentation.
FAA Response: The FAA does not agree with the comment. Special
Condition no. 1 requires that the proposed design complies with
Sec. Sec. 33.7(a), 33.7(d), as those requirements are not expressly
and explicitly applicable only to reciprocating and turbine engines.
The FAA did not change Special Condition no. 2 as a result of these
comments.
Comment Summary: TCCA stated that Special Condition no. 2, as
proposed, provided requirements ``in addition to Sec. 33.7(a),'' and
then proceeds to replace all of the Sec. 33.7 details with Special
Condition no. 2 requirements. TCCA stated the replacement of Sec. 33.7
with Special Condition no. 2, as proposed, removes the determination by
the FAA, as well as the concept of ``any other information found
necessary for the safe operation of the engine.'' TCCA indicated that
Sec. 33.7, combined with Sec. 33.8, should be referenced in the
special condition to provide the essential cornerstone for establishing
aircraft performance based on installed rated power.
FAA Response: The FAA does not agree with the comment. Special
Condition no. 1 requires that the proposed design complies with
Sec. Sec. 33.7(a), 33.7(d), and 33.8. Special Condition no. 2 provides
requirements in addition to those in Sec. 33.7(a). The concern stated
by TCCA is remedied by the inclusion of Sec. Sec. 33.7(a), 33.7(d),
and 33.8 within Special Condition no. 1. No change was made to this
special condition as a result of the comment.
Comment Summary: Regarding the reference to ``duty cycle'' in
proposed Special Condition no. 2(b), and the rating (singular) at that
duty cycle, TCCA recommended that the FAA clarify whether the duty
cycle corresponds to a flight cycle, a series of flights, or an engine
test cycle.
FAA Response: The term duty cycle in Special Condition no. 2 is an
engine rating that declares a performance capability for the load(s)
that will be imposed on the magniX engines. These capabilities are
determined by tests that may include starting, no-load and rest, de-
energized periods and their durations (or cycles), and sequence. The
FAA made no changes to the special condition as a result of the
comment.
Comment Summary: TCCA commented that proposed Special Condition no.
2 omitted consideration of electric engines' capability to regenerate
electrical power. TCCA recommended that the special conditions provide
design, construction, and testing that demonstrate this new capability,
while acknowledging that this issue is partially addressed by Special
Condition no. 31 (Operation with a variable pitch propeller).
FAA Response: Although electric engines are capable of regenerating
electrical power, these special conditions apply only to the magniX
engine designs, which are not intended to provide electrical power to
an aircraft. Therefore the FAA did not change these special conditions
as a result of this comment.
Comment Summary: TCCA suggested that the Special Condition no. 10
should be modified to include the following: ``If any electrical power
is supplied from the aircraft to the engine control system for powering
on and operating the engine, the need for and the characteristics of
this electrical power, including transient and steady-state voltage
limits, must be identified and declared in the engine installation
manual.''
FAA Response: The FAA modified Special Condition no. 2 as a result
of Wisk's comment and TCCA's comment for Special Condition no. 10. The
change requires the applicant to establish ratings and operating limits
for power-supply requirements, which include voltage and current, to be
included in the type certificate data sheet.
Comment Summary: TCCA stated that Special Condition nos. 2(a)(1)
and 2(a)(2) address power and time limits and asked if the limits are
based on an expected power supply and whether the power supply will be
part of the baseline configuration. TCCA recommended including another
special condition explaining how the power-supply characteristics will
be addressed in the declaration of power ratings and operational
limits.
FAA Response: The term ``power,'' as used in Special Condition nos.
2(a)(1) and 2(a)(2), refers to engine shaft horsepower. Special
Condition no. 2 has been modified to include the terms ``shaft power''
and ``rated takeoff power.''
Comment Summary: TCCA suggested that the FAA modify Special
Condition no. 2 to require the propeller overspeed limit to be defined
in the engine installation manual for situations involving propeller
control malfunctions. TCCA recommended that the FAA add a special
condition that requires a ``get-home'' capability.
FAA Response: The FAA does not agree with the comment. The
propeller has its own type certificate, documented ratings, and
operating limits, including an overspeed limit. These engines will also
have their own ratings and operating limits, including an overspeed
limit. Propeller overspeed protection will be managed using the engine
and propeller installation manuals' declared ratings and operating
limits. The FAA made no changes to the special condition as a result of
the comment.
Comment Summary: TCCA recommended incorporating the following text
to the special conditions: ``Each selected rating must be for the
lowest power that all engines of the same type may produce under the
conditions used to determine that rating at all times between overhaul
periods or other maintenance.''
FAA Response: Special Condition no. 1 includes a requirement for
magniX to comply with 14 CFR 33.8, so the existing requirement in part
33 is applicable to these engines. Special Condition no. 29 (Teardown
inspection) requires the engine to be within service limits and
eligible for continued operation in accordance with the information
submitted for showing compliance with Sec. 33.4, Instructions for
Continued Airworthiness. Therefore, these special conditions address
the recommendation by TCCA. The FAA made no changes to the special
condition as a result of the comment.
[[Page 53512]]
Special Condition No. 3, Materials
The FAA proposed that Special Condition no. 3 would require the
design of these engines to comply with 14 CFR 33.15, which sets
requirements for the suitability and durability of materials used in
the engine, and which would otherwise be applicable only to
reciprocating and turbine aircraft engines.
Comment Summary: Textron highlighted the potential hazards from
certain electronic components, such as aging electrolytic capacitors.
Textron recommended that the FAA require periodic testing of
electrolytic capacitors to determine an appropriate replacement
interval to avoid hazardous effects at altitude such as breakdown,
corona, flashover, creep, strike distance, and cooling.
FAA Response: These special conditions address the hazards that may
result from failure or malfunction of electronic components. Special
Condition no. 27 (System and component tests) is a performance-based
requirement in which the applicant must show that systems and
components will perform their intended functions in all declared
environmental and operating conditions. This requirement addresses all
types of component failures, including those referenced in Textron's
comment. Special Condition no. 13 (Critical and life-limited parts)
requires the applicant to 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, including
electronic parts and components. Special Condition no. 10(g) (Engine
control systems) requires the applicant to conduct a control system
safety assessment to identify the hazards resulting from control system
failures and malfunctions, such as those in Textron's comment. The FAA
made no changes to these special conditions as a result of this
comment.
Comment Summary: TCCA recommended that these special conditions
address the potential for manufacturing errors by appending the
following text: ``In addition, manufacturing methods and processes must
be such as to produce sound structure and mechanisms, and electrical
systems that retain the design properties under assumed service
conditions declared in the engine installation manual. This includes
the effects of deterioration over time, e.g., corrosion.''
FAA Response: The 14 CFR part 33 airworthiness requirement for
materials (Sec. 33.15) applies to these engines. The existing part 33
materials requirement is adequate and appropriate for the certification
basis for these engines. The FAA made no changes to the special
condition as a result of the comment.
Special Condition No. 4, Fire Protection
The FAA proposed that Special Condition no. 4 would require the
design of these engines to comply with 14 CFR 33.17, which sets
requirements to protect the engine and certain parts and components of
the airplane against fire, and which would otherwise be applicable only
to reciprocating and turbine aircraft engines. Additionally, this
special condition proposed to require magniX to ensure the high-voltage
electrical wiring interconnect systems that connect the controller to
the motor are protected against arc faults. An arc fault is a high
power discharge of electricity between two or more conductors. This
discharge generates heat, which can break down the wire's insulation
and trigger an electrical fire. Arc faults can range in power from a
few amps to thousands of amps and are highly variable in strength and
duration.
Comment Summary: GE proposed that the special conditions include a
provision for non-protected electrical wiring interconnects that
requires the applicant to conduct an analysis to show that arc faults
do not cause hazardous engine effects. GE stated that if electrical
wiring interfaces with aircraft parts or components, the potential for
arc faults should be communicated to the aircraft manufacturer. In
addition, GE recommended that the FAA require the applicant to declare
potential arc faults in the engine installation manual.
FAA Response: This special condition has provisions to prevent arc
faults in high-voltage wire interconnecting systems from causing
hazardous engine effects. Additionally, Special Condition no. 17
(Safety analysis) will have the effect of requiring magniX to account
for the intended aircraft application in the engine installation
manual. 14 CFR 33.5(c), ``Instruction manual for installing and
operating the engine,'' applies to the two magniX engines. These
requirements will generate the recommended documentation, such as
installation instructions. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: TCCA stated that no special conditions provide
standards for the electrical connectors supplied with the motor. TCCA
requested clarification of the FAA's intent.
FAA Response: The special condition is a performance-based
requirement, which allows flexibility for magniX to design and
substantiate components (such as connectors) that they use in their
engine design. The FAA made no changes to the special condition as a
result of the comment.
Special Condition No. 5, Durability
The FAA proposed that Special Condition no. 5 would require the
engine design and construction to ensure safe engine operation between
maintenance intervals, overhaul periods, and mandatory actions
described in the applicable ICA.
Comment Summary: Textron noted that the proposed wording of Special
Condition no. 5 matched the intent of 14 CFR 33.19(a) but omitted the
requirements of Sec. 33.19(b). Textron suggested that Special
Condition no. 5 include the following: ``Each component of the
propeller-blade pitch control system which is part of the engine type
design must meet the requirements of Sec. Sec. 35.21, 35.23, 35.42 and
35.43.''
TCCA provided a similar comment, asking why Sec. 33.19(b) was
omitted and seeking its inclusion in Special Condition no. 5.
FAA Response: These special conditions apply only to the two magniX
engine designs, which do not include a propeller-blade pitch control
system. The FAA made no changes to the special condition as a result of
the comments.
Comment Summary: TCCA recommended that the FAA include the
requirements from 14 CFR 33.5(b) into these special conditions, as the
controller may include propeller control functions.
FAA Response: These special conditions apply only to the proposed
magniX engine designs, which do not include propeller controls and
controllers. In addition, Special Condition no. 1 mandates compliance
with Sec. 33.5(b), Instruction manual for installing and operating the
engine, which addresses this comment. The FAA made no changes to the
special condition as a result of the comment.
Comment Summary: TCCA stated the requirements from 14 CFR 33.4 are
missing from these special conditions, but noted that including all
instructions for off-wing maintenance that were contained in the ICA,
would not be appropriate.
FAA Response: These special conditions are not intended for all
electric engine certification projects. As
[[Page 53513]]
provided in Special Condition no. 1, Sec. 33.4, Instructions for
continued airworthiness, and its appendix, apply to the magniX engines.
The FAA made no changes to the special condition as a result of the
comment.
Special Condition No. 6, Engine Cooling
The FAA proposed that Special Condition no. 6 would require the
engine design and construction to comply with 14 CFR 33.21. That
regulation requires the engine design and construction to provide
necessary cooling under conditions in which the airplane is expected to
operate and would otherwise be applicable only to reciprocating and
turbine aircraft engines. Additionally, this special condition proposed
to require the applicant to document the cooling system monitoring
features and usage in the engine installation manual, if cooling is
required to satisfy the safety analysis described in Special Condition
no. 17. Loss of adequate cooling to an engine that operates using
electrical technology can result in rapid overheating and abrupt engine
failure with critical consequences to safety.
Comment Summary: GE suggested that Special Condition no. 6 is
redundant to Special Condition no. 17 (Safety analysis) because it
includes 14 CFR 33.75(d) Safety analysis, and should be deleted.
FAA Response: The FAA does not agree with the suggested change. The
reference to Sec. 33.75(d) in Special Condition no. 17 does not
explicitly address cooling systems that are necessary for the engine to
comply with the safety analysis. Special Condition no. 6 requires
additional information about the cooling system that is not specified
in Sec. 33.75(d). The FAA made no change to Special Condition no. 6 as
a result of this comment.
Comment Summary: Ampaire suggested that, given certain assumptions,
the electric engine manufacturer may need to specify cooling limits
that cannot be exceeded at the aircraft and engine interface to ensure
safe operation.
FAA Response: The FAA does not agree with the comment. These
special conditions are applicable only to the magniX magni350 and
magni650 model engines. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: Rolls-Royce stated that the cooling system
monitoring and documentation requirements in proposed Special Condition
no. 6 are already covered in 14 CFR 33.29(h), ``Instrument
connection.'' Rolls-Royce recommended that the FAA modify Sec.
33.29(h) to include a statement of applicability to electric engines.
TCCA recommended adding, ``The cooling system monitoring must be
made available to enable the flight crew or the automatic control
system to monitor the functioning of the engine cooling system.''
FAA Response: The FAA does not agree to amend 14 CFR 33.29(h) as a
result of Rolls-Royce's comment, as these special conditions are of
particular applicability to the magni350 and magni650 model engines
only. However, as a result of Rolls-Royce's and TCCA's comments that
recommend applying cooling system monitoring to the magniX engines, the
FAA has added paragraph (b) to final Special Condition no. 11 to
incorporate the requirements of 14 CFR 33.29(h), except for those
provisions specifically applicable to turbine aircraft engines.
Comment Summary: TCCA recommended adding, ``If aspects of the
engine cooling system require the installer to ensure that the
temperature limits are met, those limits must be specified in the
installation manual.''
FAA Response: The FAA does not agree with TCCA's comment. Special
Condition no. 24 requires magniX to establish a temperature limit. If
the temperature limit is necessary for the safe operation of the
engine, these special conditions require the limit to be documented in
the installation manual. Therefore, a special condition is not needed
to mandate information specified in TCCA's comment.
Comment Summary: TCCA recommended adding, ``Any reliance placed
upon the assumed installed conditions, or installation requirements
must be declared in the instructions for installation.''
FAA Response: The FAA does not agree with TCCA's comment. Special
Condition no. 1 requires magniX to comply with 14 CFR 33.5. Therefore,
these special conditions already require the information specified in
TCCA's comment to be documented in the instructions for installing the
engine.
Comment Summary: TCCA recommended adding ``magniX must prepare and
make available to the Agency prior to the issuance of the type
certificate, and to the installer at the time of delivery of the
engine, approved instructions for installing and operating the
engine.''
FAA Response: The FAA does not agree with TCCA's comment. Special
Condition no. 1 requires magniX to comply with 14 CFR 33.4, which
requires magniX to prepare Instructions for Continued Airworthiness in
accordance with appendix A to that part. Appendix A requires the
Instructions for Continued Airworthiness include instructions for
installing and operating the engine. Special Condition no. 1 also
mandates compliance with 14 CFR 33.5, which requires magniX to prepare
and make available to the Administrator, prior to the issuance of the
type certificate, and to the owner at the time of delivery of the
engine, approved instructions for installing and operating the engine.
The FAA made no changes to the special condition as a result of the
comment.
Special Condition No. 7, Engine Mounting Attachments and Structure
The FAA proposed that Special Condition no. 7 would require these
engines to comply with 14 CFR 33.23, which requires the applicant to
define the proposed design to withstand certain load limits for the
engine mounting attachments and related engine structure. These
requirements would otherwise be applicable only to reciprocating and
turbine aircraft engines.
Comment Summary: Textron stated that a propeller could be a much
higher percentage of the total propulsion system mass in electric
systems than for reciprocating or turbine engine propulsion systems and
suggested that an electric motor's rotating components can be nearly
instantly coupled to the non-rotating components due to FOD, internal
failure, rotor growth, and commutation errors. Textron proposed
additional requirements to Special Condition no. 7 related to sudden
stoppage and bearing protection to ensure the engine mounting system
can absorb the load or mitigate the effect of the load on aircraft.
FAA Response: The FAA does not agree with the comment. The
certification basis for the proposed engines includes 14 CFR 33.23,
Engine mounting attachments and structure, which is a performance-based
requirement. The regulation doesn't specify how maximum and ultimate
loads are determined because these load conditions are determined by
magniX. Also, Special Condition no. 2 requires magniX to establish a
torque limit and Special Condition no. 21 requires magniX to establish
a maximum overtorque limit. These requirements address the conditions
described in Textron's comment. magniX's engines must be designed to
accommodate the load at these limit values. These special conditions
address high engine mount load conditions, including the conditions
described in Textron's comment, except for loads from the
[[Page 53514]]
failure considerations that are normally addressed by Special Condition
no. 17 (Safety Analysis). The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: Textron recommended adding a requirement for
bearing protection that states, ``Engine bearings must be protected
from rotor voltage or a periodic replacement interval shall be
determined as defined in Special Condition no. 13.''
FAA Response: The FAA agrees with the technical content of this
comment, but there is no requirement in these special conditions to add
rotor shaft grounding technology in the magniX engines. Bearings could
experience accelerated wear-out from ungrounded shafts, but the failure
should not present a safety issue because the failure is predictable
with sufficient testing. Requirements such as Sec. 33.4, Instructions
for Continued Airworthiness, Special Condition no. 3 (Materials),
Special Condition no. 5 (Durability), Special Condition no. 13
(Critical and life-limited parts), and Special Condition no. 29
(Teardown inspection) will all have a role in managing the consequences
of potential bearing wear from electrical effects. magniX may assess
the impact to product support at the predicted bearing replacement
frequency and decide to include rotor shaft grounding technology.
Comment Summary: TCCA recommended that the FAA add a requirement to
this special condition, requiring the applicant to demonstrate that the
engine mounts and mounting features are fireproof if flammable fluids
are used within the engine.
FAA Response: The FAA does not agree with the comment. The fire
protection requirements in 14 CFR 33.17 apply to the magniX engines.
The FAA made no changes to the special condition as a result of the
comment.
Special Condition No. 8, Accessory Attachments
The FAA received no comments for Special Condition no. 8, and it is
adopted as proposed. It requires the engine to comply with 14 CFR
33.25, which sets certain design, operational, and maintenance
requirements for the engine's accessory drive and mounting attachments,
and which would otherwise be applicable only to reciprocating and
turbine aircraft engines.
Special Condition No. 9, Overspeed
The FAA proposed that Special Condition no. 9 would require magniX
to establish by test, validated analysis, or a combination of both,
that: (1) The rotor overspeed not result in a burst, rotor growth, or
damage that results in a hazardous engine effect; (2) rotors possess
sufficient strength margin to prevent burst; and (3) operating limits
of the engine not be exceeded in-service.
Comment Summary: GE stated that proposed Special Condition no. 9(c)
was duplicative of Special Condition no. 10(b) and (h) (Engine control
systems), and requested the special condition be removed.
FAA Response: The FAA does not agree with the comment. The special
conditions referenced by GE accomplish different safety objectives.
Special Condition no. 9(c) requires that the engine must not exceed the
rotor speed operational limitations that could affect rotor structural
integrity. This requirement results in an overspeed limit. Special
Condition no. 10(b) requires 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. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: Ampaire stated that Special Condition no. 9
(Overspeed) should include more information from ASTM F3338-18.
FAA Response: The FAA does not agree with the comment. ASTM F3338-
18 section 5.9, EPU Rotor Overspeed, contains technical criteria that
the FAA used in developing these special conditions. It also contains
information that the applicant can use to propose means of compliance
to these special conditions. The FAA did not change this special
condition as a result of this comment.
Comment Summary: Textron recommended that the FAA modify Special
Condition no. 9, paragraphs (a) and (c), replacing ``speed'' with
``RPM.'' Textron reasoned that the term ``speed'' could be misleading.
FAA Response: The units used for rotational speed in the
limitations section of the engine manual can be expressed using various
units. The FAA recognizes that ``rpm'' is used in 14 CFR 33.88, Engine
overtemperature test and Sec. 33.201, Design and test requirements for
Early ETOPS eligibility, but speed units are not specified in all
regulations that mention engine rotor speed. Therefore, the FAA will
maintain the term ``speed'' in these special conditions. The FAA did
not change this special condition as a result of this comment.
Comment Summary: TCCA stated that proposed Special Condition no. 9
suggested that the controller will provide the engine overspeed
protection and commented that the FAA should ensure that the overspeed
protection will function as intended when exposed to high-intensity
radiated fields (HIRF), lightning environments, and threats. TCCA
stated that verification of this protection might require the electric
motor and engine control system to be included in the test setup when
conducting the HIRF and lightning transient system tests and
recommended that these special conditions clarify this topic in the
discussion section of these special conditions.
FAA Response: This special condition is a performance-based
requirement, and test details will be established as part of the
demonstration of compliance. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: TCCA recommended that the FAA modify ``Rotors must
possess'' as stated in Special Condition no. 9(b), to ``Rotors,
including any integral fan rotors used for cooling, must possess.''
FAA Response: These special conditions are not generally applicable
to all electric engines; they apply only to the applicant's proposed
engines. The magniX engines do not use integral fan rotors to cool the
engine. The FAA did not change this special condition as a result of
the comment.
Special Condition No. 10, Engine Control Systems
The FAA proposed that Special Condition no. 10 would impose several
requirements.
Special Condition no. 10(a) proposed that the requirements of that
special condition apply to any engine system or device that controls,
limits, monitors, or protects engine operation and is necessary for the
continued airworthiness of the engine.
Special Condition no. 10(b) proposed to require that an engine
control system ensure that the engine does not experience any
unacceptable operating characteristics (such as unstable speed or
torque control) or exceed any of its operating limits.
Special Condition no. 10(c) proposed to require magniX to
systematically design, develop, and verify the software and complex
electronic hardware, including programmable logic devices. RTCA DO-254,
Design Assurance Guidance for Airborne Electronic
[[Page 53515]]
Hardware, dated April 19, 2000,\6\ distinguishes between complex and
simple electronic hardware.
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Special Condition no. 10(d) proposed to require the applicant to
substantiate all functional aspects of the control system to show that
it performs its intended functions throughout the declared operational
envelope.
Special Condition no. 10(e) proposed to require the system and
component tests in Special Condition no. 27 to demonstrate the control
will function as intended at environmental limits that magniX cannot
otherwise substantiate. These limits include temperature, vibration,
HIRF, and other limits addressed in RTCA DO-160G, Environmental
Conditions and Test Procedures for Airborne Electronic/Electrical
Equipment and Instruments \7\ (DO-160G) or other appropriate industry
standards for airborne environmental-conditions testing, such as Mil-
STD-810 ``Environmental Engineering Considerations and Laboratory
Tests,'' Mil-STD-202 ``Test Method Standard for Electronic and
Electrical Component Parts,'' Mil-461 ``Requirements for the Control of
Electromagnetic Interference Characteristics of Subsystems and
Equipment,'' and those listed in Advisory Circular 21-16G, RTCA
Document DO-160 versions D, E, F, and G, ``Environmental Conditions and
Test Procedures for Airborne Equipment,'' Special Condition no. 10(e)
also requires magniX to document the environmental limits to which the
system has been qualified in the engine installation manual.
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Special Condition no. 10(f) proposed to require the engine control
system not to exceed a maximum rate of Loss of Power Control (LOPC) for
the aircraft types that will use the magniX engines, be single-fault
tolerant in the full-up configuration, not have any single failure that
results in hazardous engine effects, and not have any likely failure or
malfunction that lead to local events in the intended installation.
The FAA issued Advisory Circular AC 33.28-3, Guidance Material For
14 CFR 33.28, Engine Control Systems, on May 23, 2014.\8\ Paragraph 6-2
of this AC provides applicants with guidance about defining an engine
control system failure when showing compliance with the requirements of
Sec. 33.28. It also explains the safety objectives of the
requirements, provides criteria for a loss of thrust control (LOTC)/
LOPC events for reciprocating and turbine engines. However, the
guidance in AC 33.28-3 may not have sufficient information to identify
failure modes and establish acceptable LOTC/LOPC rates for the magniX
electric engines because electric engines did not exist when the FAA
issued this AC.
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The phrase ``in the full-up configuration'' used in Special
Condition no. 10(f)(2) refers to a system without any fault conditions
present. When in the full-up configuration, the electronic control
system must be single fault tolerant for electrical, electrically
detectable, and electronic failures involving LOPC events.
The term ``local events'' used in Special Condition no. 10(f)(4)
means failures or malfunctions that could lead to hazardous effects
such as fire, overheat, or failures causing damage to engine control
system components.
Special Condition no. 10(g) proposed to require magniX to conduct a
system safety assessment to support the safety analysis in Special
Condition no. 17.
Special Condition no. 10(h) proposed to require that the design and
function of the engine control devices and systems, together with the
engine instruments, operating instructions, and maintenance
instructions, ensure that engine operating limits will not be exceeded
in-service.
Special Condition no. 10(i) proposed to protect the airplane and
engine from single failures relating to the aircraft-supplied data by
mandating that the control system is able to detect and accommodate
such failures, and not result in a hazardous engine effect.
The term ``independent,'' as it is used in ``fully independent
engine systems,'' means that the controllers should be either self-
sufficient and isolated from other aircraft systems or provide
redundancy. In the case of loss, interruption, or corruption of
aircraft-supplied data, the engine must continue to function without
hazardous engine effects.
The term ``accommodated'' means that when a fault has been
detected, the system must continue to function safely.
Special Condition no. 10(j) proposed to require magniX to show that
the loss, malfunction, or interruption of the control system electrical
power source will not result in a hazardous engine effect, the
unacceptable transmission of erroneous data, or continued engine
operation in the absence of the control function.
Comment Summary: Rolls-Royce asked that the FAA clarify the
requirements contained in Special Condition nos. 10(f)(1) and (f)(2).
The commenter expressed concern that the single fault tolerance
requirement in Special Condition no. 10(f)(2) would be applied to both
historical electrical elements of the engine control system and to the
new high-voltage electrical/electronic elements required to motivate an
electric motor. Rolls-Royce commented that it was possible the wording
of this condition would be extended to cover loss of power (LOP) events
due to the difficulties of establishing the boundary between the
control and the motor drive in an electric engine. Rolls-Royce asked
the FAA to modify this special condition to clarify that the degree of
fault tolerance in the high-voltage electrical/electronic elements will
be governed by the LOP reliability requirement of Special Condition no.
10(f)(1), and not the single fault tolerance requirement of LOPC of
Special Condition no. 10(f)(2). AIAB articulated a similar concern and
recommended the FAA delete Special Condition no. 10(f)(2) in these
final special conditions. AIAB stated a loss of thrust control (LOTC)/
LOPC event could be considered minor in aircraft with distributed
propulsion, and therefore may not require electrical redundancy.
FAA Response: The comments from Rolls-Royce and AIAB describe the
potential dependency between the electric engine safety analysis and
certain aircraft configurations, and the potential effect the aircraft
design could have on the need for engine design redundancy. However,
magniX designed these engines for certain aircraft configurations that
do not have special flight control capabilities, which is why the LOPC
and single fault tolerance criteria from 14 CFR part 33 are adopted in
these special conditions. The FAA also included ``suitable for the
intended aircraft application'' in Special Condition no. 10(f)(1), and
``as determined by the Administrator'' in Special Condition no.
10(f)(2) ``Engine control system failures'' to constrain the use of
these engines to aircraft that are designed with compatible engine
safety assumptions. Therefore, the FAA did not change these special
conditions as a result of this comment.
Comment Summary: TCCA commented that the FAA's introductory text to
proposed Special Condition no. 10(e), ``Environmental limits,''
indicated that the environmental limits are addressed in DO-160G.
However, TCCA suggested that some of the test specifications, methods,
and categories in DO-160G might not be adequate for high-voltage
systems such as the high-voltage components of this engine. TCCA
suggested that the FAA modify Special Condition no. 10(e) to require
[[Page 53516]]
that the applicant establish and demonstrate the environmental limits
of the engine for those circumstances when the standards in DO-160G may
not be adequate.
FAA Response: These special conditions are applicable to this
applicant's project and are not generally applicable requirements. As
such, the FAA will evaluate the approach that the applicant proposes to
substantiate the compliance of their design's high-voltage systems. The
FAA made no changes to these special conditions as a result of this
comment.
Comment Summary: TCCA noted that in the introduction to proposed
Special Condition no. 10(f), the FAA stated that ``As with other topics
within these proposed special conditions, the failure rates that apply
to electric engines were not established when the FAA issued this AC''
[referring to AC 33.28-3]. TCCA stated that the referenced FAA guidance
document might not have sufficient data to allow an applicant to
substantiate the selected failure modes and failure rates applicable to
the electrical engine and associated high-voltage systems. TCCA
recommended that the FAA clarify the statement in the discussion and
note that the applicant has the responsibility to substantiate the
failure modes and rates to show compliance to these special conditions.
FAA Response: The FAA added clarification to the discussion of
Special Condition no. (10)(f).
Comment Summary: TCCA asked the FAA to clarify whether the engine
cockpit controls are part of the configuration discussed in Special
Condition no. 10. TCCA also recommended that the FAA require the
applicant to conduct a human error assessment to mitigate the effects
of crew mistakes due to electric engine cockpit controls if they are
different from conventional engine cockpit controls.
FAA Response: The engine cockpit controls are not part of the
engine configuration. No changes to these final special conditions are
required to address TCCA's comment.
Comment Summary: TCCA requested that Special Condition no. 10(a)
use similar wording as 14 CFR 33.28(a). TCCA stated that such wording
could affect the applicant's understanding of the requirement because
the proposed words indicate Special Condition no. 10(a) could also be
applicable to a system or a device that is not part of the engine type
design.
FAA Response: In these final special conditions, the FAA has
modified Special Condition no. 10(a) to incorporate the purpose of 14
CFR 33.28(a).
Comment Summary: TCCA stated proposed Special Condition no. 10(j)
requires that the loss, malfunction, or interruption of the electrical
power to the engine control system not result in a hazardous engine
effect, the unacceptable transmission of erroneous data, or continued
engine operation in the absence of the control function. TCCA stated
that this special condition does not require the engine control system
to be capable of resuming normal operation when the electrical power
returns to a normal state. TCCA commented that the electrical power
source could be subject to transients resulting in a temporary effect
on the output power and shut down the control system and/or engine.
TCCA explained once the temporary transients cease, the engine control
system should be capable of resuming normal operation when the power
characteristics return to the normal range (similar to the requirements
of (14 CFR) 33.28(i)(4). TCCA proposed adding a subparagraph to Special
Condition no. 10(j) to require, ``Voltage transients outside the power-
supply voltage limitations declared in SC 10(j)(2) must meet the
requirements of SC no. 10(j)(1). The engine control system must be
capable of resuming normal operation when electrical power returns to
within the declared limits.''
FAA Response: A special condition is not required to specify
requirements for voltage transients that are outside the power-supply
voltage limitations declared in Special Condition no. 10(j)(2),
``Engine control system electrical power'' because exceedances to these
limitations are addressed by Special Condition no. 10(h), ``Protection
systems.'' Special Condition no. 10(j)(1) corresponds to 14 CFR
33.28(i), which includes the additional requirement TCCA recommended.
The FAA added, ``The engine control system must be capable of resuming
normal operation when aircraft-supplied power returns to within the
declared limits'' to Special Condition no. 10(j)(1) as a result of this
comment.
Comment Summary: TCCA stated Special Condition no. 10 is similar to
the current 14 CFR 33.28 requirement. TCCA suggested modifying Special
Condition no. 10 to state, ``The engine design must comply with 14 CFR
33.28.''
FAA Response: 14 CFR 33.28 is applicable to reciprocating and
turbine aircraft engines. The airworthiness regulations in 14 CFR 33.28
do not contain adequate or appropriate safety standards for the
magni350 and magni650 model engines because of a novel or unusual
design feature (use of electrical energy source instead of aviation
fuel to drive the mechanical systems). Section 33.28 contains design
requirements that do not apply to the proposed engines. The FAA did not
change these special conditions as a result of this comment.
Comment Summary: TCCA recommended that Special Condition no. 10(j)
require the applicant to define and declare, in the engine installation
manual, the characteristics of the electrical power supplied to the
engine control system, as required by 14 CFR 33.28(i)(3).
FAA Response: The FAA has added a subparagraph to Special Condition
no. 10(j) ``Engine control system electrical power,'' which requires
magniX to identify and declare the characteristics of any electrical
power supplied from the aircraft to the engine control system for
starting and operating the engine, including transient and steady-state
voltage limits, and any other characteristics necessary for the safe
operation of the engine in the engine installation manual.
Comment Summary: TCCA recommended that Special Condition no. 10
require a means to shut the engine down rapidly.
FAA Response: Special Condition no. 17(d)(2) incorporates 14 CFR
33.75(g)(2)(vii), which includes, as a hazardous engine effect, the
complete inability to shut the engine down. The FAA made no changes to
these special conditions as a result of this comment.
Comment Summary: TCCA commented that the proposed special
conditions do not address the emerging issue of cybersecurity. Since
the FAA is currently addressing this issue with an issue paper, TCCA
recommended incorporating the issue paper into Special Condition no. 10
by reference.
TCCA also recommended that the FAA address cybersecurity by adding
a special condition that states, ``Information system security
protection. Engine control systems, including networks, software, and
data, must be designed and installed so that they are protected from
intentional unauthorized electronic interactions (IUEI) that may result
in adverse effects on the safety of the aircraft. The security risks
and vulnerabilities must be identified, assessed, and mitigated as
necessary. The applicant must make procedures and instructions for
continued airworthiness (ICA) available that ensure that the security
protections of the engine controls are maintained.''
FAA Response: The FAA does not agree with the comment. A special
condition for cybersecurity is not
[[Page 53517]]
needed for the magniX engine design. Cybersecurity issues are not
specific to these magniX engines and will be addressed by other
compliance determinations. The FAA made no changes to these special
conditions as a result of this comment.
Comment Summary: Wisk stated that the change in wording from 14 CFR
33.28 from ``Operating limits'' to ``Operating limitations'' could have
uncertain impacts, as ``limits'' are typically parametric-based and
mostly achievable by a control system if so required. Wisk noted that
operating limitations are more aligned to what is found in an airplane
flight manual, so this expands the scope of what the control system may
be expected to do.
FAA Response: The FAA has changed ``operating limitations'' to
``operating limits'' in Special Condition no. 10(b).
Comment Summary: Wisk asked what the FAA meant by ``be single fault
tolerant, as determined by the Administrator'' in proposed Special
Condition no. 10(f)(2).
FAA Response: The term ``single fault tolerant'' describes an
engine control system's ability to experience single failures and not
result in a hazardous engine effect while operating without any fault
conditions present and in all dispatchable configurations. Special
Condition no. 10(f)(2) requires the engine control system to be single
fault tolerant for electrical, electrically detectable, and electronic
failures involving LOPC events. The FAA made no changes to these
special conditions as a result of this comment.
Comment Summary: Wisk asked that the FAA clarify the meaning of
``local events'' as used in proposed Special Condition no. 10(f)(4)
``Engine control system failures.''
FAA Response: The term ``local events'' used in Special Condition
no. 10(f)(4) means failures or malfunctions that could lead to
hazardous effects such as fire, overheat, or failures causing damage to
engine control system components. The FAA made no changes to these
special conditions as a result of this comment.
Comment Summary: Wisk suggested that the FAA not impose proposed
Special Condition no. 10(g), ``System safety assessment.'' Wisk stated
that the condition was unnecessary and could lead to uncertainty
because 14 CFR 33.75(a), Safety analysis, is more rigorous. Wisk
suggested incorporating Sec. 33.75(a)(1) into Special Condition no.
10, or linking Special Condition no. 17 to Special Condition no. 10(g).
FAA Response: Special Condition no. 17 (Safety Analysis),
incorporates 14 CFR 33.75(a)(1), which requires the applicant to
analyze the engine, including the control system, to assess the likely
consequences of all failures that can reasonably be expected to occur.
Special Condition no. 10, which is adopted as proposed, contains a
separate requirement for the engine control, including the frequency of
occurrence of faults or failures. The linkage requested by Wisk between
the engine safety analysis and control system safety assessment exists
in these special conditions. The FAA made no changes to these special
conditions as a result of this comment.
Comment Summary: Wisk stated they understood the initial intent of
Sec. 33.28(i) around engine controllers being reliant on electrical
power for function, whereby fuel was used for the production of useful
thrust/power. Wisk commented that by stating the engine control must
accommodate any `malfunction' of the electrical supply forces the
engine control to accommodate overvoltage, overcurrent, etc., that may
drive unnecessary cost and weight on the engine manufacturer. Wisk
recommended consideration is given to the high-voltage electrical
source used for thrust/power generation such that it is treated more
like fuel, which is under the control of the airframe OEM.
FAA Response: Special Condition no. 10(j) does not require the
magniX engine controller to accommodate malfunctions of the electrical
supply. The special condition requires the engine control system to be
designed such that a loss, malfunction, or interruption of the control
system electrical power source will not result in hazardous engine
effects. However, Special Condition no. 2 requires magniX to establish
and declare ratings and operating limits based on power-supply
requirements for the engine, which addresses the suggestion proposed by
Wisk. The FAA did not change this special condition as a result of this
comment.
Comment Summary: Ampaire asked the FAA to incorporate additional
information from ASTM F3338-18 section 5.10, EPU Controls, into Special
Condition no. 10(g), system safety assessment, and Special Condition
no. 10(h), protection systems.
FAA Response: ASTM F3338-18 contains technical criteria that the
FAA incorporated in these special conditions. It also contains
information that the applicant can use to develop a means of compliance
to these special conditions. The FAA did not change these special
conditions as a result of this comment.
Comment Summary: AIAB proposed that the FAA mandate compliance with
14 CFR 33.28(h)(2). AIAB stated that the accommodation strategy could
depend on the aircraft that use the engines because the aircraft's
response to a change to thrust or power will determine if the
accommodation strategy is acceptable. AIAB asked that the FAA require
the applicant to evaluate the effects of aircraft-supplied data
failures and document them in the engine installation manual.
FAA Response: As a result of this and other comments, the FAA
modified Special Condition no. (10)(g) by adding, ``The intended
aircraft application must be taken into account to assure the
assessment of the engine control system safety is valid.'' Therefore,
the applicant's fault accommodation strategies will need to account for
the aircraft's capabilities. If the accommodation strategy meets any
criteria in 14 CFR 33.5, that regulation will prompt magniX to document
the details in the Instruction manual for installing and operating the
engine. The FAA has changed the special condition to include additional
requirements for aircraft-supplied data consistent with the
recommendation.
Comment Summary: An anonymous commenter inquired if these special
conditions would address electromagnetic interference potential, which,
the commenter states, has caused issues with onboard radios and
equipment.
FAA Response: Special Condition no. 10(e), Environmental limits,
addresses potential engine effects from HIRF and lightning, as well as
electromagnetic compatibility between the engine and aircraft systems.
This special condition also requires the applicant to document the
environmental limits to which the system has been qualified and the
electromagnetic emissions from the engine. The FAA made no changes to
these special conditions as a result of this comment.
Comment Summary: Textron stated the proposed Special Condition no.
10(h) matches the requirements of Sec. 33.28(f)(1), but the
requirements of Sec. 33.28(f)(2) and (f)(3) are not included. Textron
also stated there is no obvious reason why the same requirements for
overspeed protection would not also apply to an electric engine, so
those requirements should be added to the proposed special condition.
FAA Response: These special conditions are applicable only to the
magniX magni350 and magni650 model engines. Special condition 10(h)
ensures the magniX operating limits will not be exceeded in-service.
The FAA made no changes to these special conditions as a result of this
comment.
[[Page 53518]]
Comment Summary: Textron recommended that the FAA add the following
to the end of Special Condition no. 10(b), ``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.'' Textron reasoned that 14 CFR
33.28(c) addresses failures resulting in changes to the operation of
the engine and that regulatory requirements should be applicable to
electric engines.
FAA Response: Special Condition no. 10 (Engine control systems)
addresses the potential for all control system failures and failure
effects, including failure or malfunction during control system
transitions during a rotor overspeed. However, in these final special
conditions, the FAA has changed Special Condition no. 10(b) as a result
of this comment to include 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.
Special Condition No. 11, Instrument Connection
The FAA proposed that Special Condition no. 11 would require magniX
to comply with 14 CFR 33.29(a), (e), (f), and (g), and, as part of the
required system safety assessment, assess the possibility and
subsequent effect of incorrect fit of instruments, sensors, or
connectors.
Comment Summary: Wisk referred to the statement, ``In addition, as
part of the system safety assessment of Special Condition no. 10(g)''
and recommended that the FAA replace the citation in Special Condition
no. 11 with reference to Special Condition no. 17 or 14 CFR
33.75(a)(1).
FAA Response: Special Condition no. 10(g) requires a separate
safety assessment for the engine control system. The engine control
system safety assessment is not addressed by Special Condition no. 17
or 14 CFR 33.75(a)(1), which requires an engine-level safety analysis.
The engine-level safety analysis does not go into enough detail to
address the effects of control system failures and malfunctions. The
FAA did not modify this special condition as a result of this comment.
Comment Summary: Textron stated, Special Condition no. 11 mandates
compliance with 14 CFR 33.29(f), thereby requiring the applicant to
assess the possibility and subsequent effects of incorrect fit of
instruments, sensors, or connectors. Textron considered this
requirement to repeat the assessments required by Special Condition no.
10(g) (Engine control systems). For this reason, Textron recommended
removing the provisions in Special Condition no. 11 that are adopted by
reference to Sec. 33.29(f).
FAA Response: Special Condition no. 10(g) corresponds to Sec.
33.28(e), which requires an engine control systems safety assessment.
However, Sec. 33.29(f) requires that, as part of the System Safety
Assessment of Sec. 33.28(e), the applicant must assess the possibility
and subsequent effect of incorrect fit of instruments, sensors, or
connectors. Therefore, Special Condition no. 11 does not repeat the
requirements in Special Condition 10(g). After reviewing Textron's
comment, the FAA removed reference to Sec. 33.29(f) because the
content of that regulation is captured within Special Condition no.
11(a). The FAA made no changes to the special condition as a result of
the comment.
Comment Summary: TCCA recommended that the FAA add a provision
requiring that instrument or sensor connections be designed or labeled
to ensure a correct connection.
FAA Response: The FAA does not agree with the comment. Special
Condition no. 11 applies 14 CFR 33.29(a) to the magniX engines, so this
special condition already requires that the connections meet the
criteria specified in TCCA's comment. The FAA made no changes to the
special condition as a result of the comment.
Comment Summary: TCCA recommended adding the following to Special
Condition no. 11: ``Any instrumentation on which the Safety Analysis
(see special condition no. 17) depends must be specified and declared
mandatory in the engine installation manual.''
FAA Response: The certification basis for the proposed engines
includes 14 CFR 33.5(a)(6), 33.5(c), and Special Condition no. 17(c),
which encompasses Sec. 33.75(d) and Sec. 33.75(e). These requirements
will achieve the desired results recommended in this comment. The FAA
did not change these special conditions as a result of this comment.
Special Condition No. 12, Stress Analysis
14 CFR 33.62 requires a stress analysis be performed on each
turbine engine. The requirement is applicable only to turbine engines
and turbine engine components, and therefore, is not appropriate for
the magni350 and magni650 Model engines. The FAA proposed this special
condition due to the need for a stress analysis of similar components
used in these proposed engines.
The FAA proposed that Special Condition no. 12 would require a
mechanical, thermal, and electromagnetic stress analysis that showed a
sufficient design margin to prevent unacceptable operating
characteristics. Also, the condition proposed to require the applicant
to determine the maximum stresses in the engine by tests validated
analysis, or a combination thereof and show that they do not exceed
minimum material properties.
Comment Summary: Wisk asked the FAA to clarify this special
condition by declaring the types of failure effects that the special
condition addresses. Wisk stated that Special Condition no 12 refers to
``unacceptable operating characteristics'' and that this term, coupled
with Special Condition no. 9, may leave a gap where no analysis is
required for static structural components (mounts, casings, etc.),
which would not affect operating characteristics but could still be
hazardous.
FAA Response: The corresponding 14 CFR part 33 airworthiness
requirement for this special condition is Sec. 33.62 Stress analysis.
The corresponding part 33 airworthiness requirement for Special
Condition no. 9 (Overspeed) is Sec. 33.27, Turbine, compressor, fan,
and turbosupercharger rotor overspeed. These special conditions are
intended to apply similar requirements to the magniX engines but with
additional provisions to account for electric engine technology. The
additional analysis suggested in Wisk's comment is already required by
Special Condition no. 13 (Critical and life-limited parts). It requires
a stress analysis of static engine parts, so no changes were made to
this special condition as a result of this comment.
Comment Summary: TCCA recommended that the FAA require the
applicant to provide an analysis of electromagnetic stresses.
FAA Response: The FAA concurs with this comment. The FAA has
modified Special Condition no. 11 to require the analysis to assess the
impact of electromagnetic interference on stress.
Comment Summary: TCCA recommended adding, ``The sufficient design
margin must be established in the means of compliance'' to Special
Condition no. 12(a).
FAA Response: Design margin is already required by Special
Condition no. 12 (Stress Analysis), which will require magniX to
develop the compliance documents suggested by
[[Page 53519]]
TCCA. In addition, design margins are also required by Special
Condition nos. 9 (Overspeed), 12 (Stress Analysis), 19 (Liquid
Systems), 24 (Temperature Limit), and 30 (Containment). No changes have
been made to this special condition as a result of this comment.
Special Condition No. 13, Critical and Life-Limited Parts
The FAA proposed that Special Condition no. 13 would require magniX
to show 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.
Special Condition no. 13 corresponds to 14 CFR 33.70, Engine life-
limited parts, which is a complex requirement. Accordingly, additional
information is provided in this discussion. In this context, the
engineering plan referenced in Special Condition no. 13(b)(1) requires
magniX to establish activities for managing documents, practices, and
procedures that govern essential design criteria essential to part
airworthiness. The engineering plan contains methods for verifying the
characteristics and qualities assumed in the design data. The methods
must be suitable for the part criticality. The engineering plan
communicates information from engineering to manufacturing about the
criticality of design features that affect airworthiness. In accordance
with 14 CFR 21.137, Quality system, the plan must include a reporting
system that flows problematic issues that develop while operating in-
service so the applicant's design process can address them. The
engineering plan is established during pre-certification activities and
executed during post-certification activities.
For example, the effect the environment has on engine performance
might not be consistent with the design assumptions. The impact of ice
slab ingestion on engine parts might not be fully understood until the
engine response is evaluated during testing the specific ice quantities
and shapes that the airplane sheds.
The term ``low-cycle fatigue,'' as referenced in Special Condition
no. 13(a)(2), is a decline in material strength from exposure to cyclic
stress at levels beyond the stress threshold the material can sustain
indefinitely. This threshold is known as the material endurance limit.
Low-cycle fatigue typically causes a part to sustain plastic or
permanent deformation during the cyclic loading and can lead to cracks,
crack growth, and fracture. Engine parts that operate at high-
temperatures and high-mechanical stresses simultaneously can experience
low-cycle fatigue coupled with creep. Creep is the tendency of a
metallic material to permanently move or deform when exposed to the
extreme thermal conditions created by hot combustion gasses and
substantial physical loads such as high rotational speeds and maximum
thrust. Conversely, high-cycle fatigue is caused by elastic
deformation, small strains caused by alternating stress, and a much
higher number of load cycles compared to the number of cycles that
cause low-cycle fatigue.
The term ``manufacturing definition,'' as referenced in Special
Condition no. 13(b)(2), means the collection of data required to
translate documented engineering-design criteria into physical parts
and verify that the parts comply with the design data properties.
Because FAA regulations do not require parts to fail during a
certification program, the documents and processes have outcome
expectations, required by 14 CFR 21.137, Quality system and 14 CFR
21.138, Quality manual, to result in parts with the integrity and
reliability assumed in the design data. These production and quality
systems limit the potential manufacturing outcomes to parts that are
consistently produced within physical design constraints.
The manufacturing plan and service management plan ensure essential
information from the engineering plan, such as the design
characteristics that ensure the integrity of critical and life-limited
parts, is consistently produced and preserved over the lifetime of
those parts. The manufacturing plan includes special processes and
production controls to prevent manufacturing-induced anomalies, which
can degrade the part's structural integrity. Examples of manufacturing-
induced anomalies are material contamination, unacceptable grain
growth, heat affected areas, and residual stresses. The service
management plan has provisions for enhanced detection and reporting of
service-induced anomalies that can cause the part to fail before
reaching its life-limit or service limit. Abnormalities can develop in-
service from improper handling, unforeseen operating conditions, and
long-term environmental effects. The service management plan ensures
important information that might affect the design process's
assumptions is incorporated into the design process to remove
unforeseen potential unsafe features from the engine.
Comment Summary: Wisk stated it is more appropriate to use ``The
Applicant'' than the Company name ``magniX'' in Special Condition no.
12(b)(1). Wisk recommended changing the reference to the engine
manufacturer reference from ``magniX'' to ``the applicant.''
FAA Response: The FAA understands Wisk's comment to be relevant to
Special Condition no. 13(b)(1) because Special Condition no. 12(b)(1)
does not exist. These special conditions are not applicable to all
electric engine manufacturers. As stated in this preamble, these
special conditions apply to the magniX magni350 and magni650 model
engines. No change to this special condition is necessary as a result
of this comment.
Comment Summary: Textron recommended that the post-certification
activities described in the Discussion section of the proposed special
conditions be included in the text of Special Condition no. 13.
FAA Response: The Discussion for this special condition is based on
its similarity to 14 CFR 33.70, Engine life-limited parts. No change to
this special condition is necessary as a result of this comment.
Comment Summary: An individual commenter suggested there might be
unique questions regarding low-cycle fatigue (LCF) of components used
in electric engines. The commenter explained that if the core rotor
speed is low, the risk of a rotor burst might not be significant.
However, a core rotor assembly that uses windings or embedded permanent
magnets (if applicable) may have some LCF/thermal/electrical (refer to
corona effect on motor windings) cycling challenges and the
electrically powered electronics driving the motor. The individual also
stated that they have learned through experience about the significance
of thermal effects resulting from a broad range of operating
conditions, especially during quick power transients.
FAA Response: Special Condition no. 13 requires magniX to determine
the parts and components that should be classified designed,
manufactured and managed throughout their service life as critical or
life-limited parts. Therefore, Special Condition no. 13 provides the
requirements for magniX to address the unique issues that arise when
identifying and managing life-limited and critical electric engine
parts. The FAA made no changes to these special conditions as a result
of this comment.
Comment Summary: TCCA stated that 14 CFR 33.70 is similar enough to
proposed Special Condition no. 13 that the FAA should replace the
proposed special condition with reference to the 14 CFR part 33
requirement and modify it. EASA suggested the FAA remove the
[[Page 53520]]
term ``Critical Parts'' from this special condition.
FAA Response: Section 33.70 prescribes a mandatory replacement
interval for turbine engine parts that are likely to fail from fatigue
if they are not removed from service. The failure can cause a hazardous
engine effect. Section 33.70 does not address parts that have a
different primary failure mode than fatigue but can still fail in a way
that causes a hazardous engine condition. Electric engine technology
operates using electromagnetic technology and physical properties that
are different than those of turbine engines. This is why the special
condition has requirements for ``critical'' parts. Therefore, there is
a need for a special condition that addresses failures of parts and
components caused by the properties related to the novel technology
used in these proposed engines. Further, the FAA currently uses the
term ``critical parts'' to describe certain parts approved under 14 CFR
part 21 subpart K, Parts Manufacturer Approval and in 14 CFR part 35,
Airworthiness Standards: Propellers. The use of the term ``critical
parts'' in these special conditions is consistent with the FAA's use of
the term as it applies to conventional engines. The FAA did not change
these special conditions as a result of these two comments.
Comment Summary: TCCA asked that these special conditions define
``primary failure'' as failures that are not the result of a prior
failure of another part or system.
FAA Response: The term ``primary failure'' is used in 14 CFR 33.70,
and this special condition is based on the requirements in that
section. The FAA did not change these special conditions as a result of
this comment, but the suggested clarification is adopted in the
discussion to Special Condition no. 17.
Comment Summary: AIAB proposed that the FAA require the assumptions
used by the applicant in the life-limited parts analysis to be declared
in the engine installation manual, should the FAA certify the engine
with no associated aircraft.
FAA Response: Final Special Condition nos. 10(g) and 17(e) require
magniX to account for the intended aircraft application for the engine
safety analysis and engine control systems safety assessment to be
valid, so there will be no need to account for engines with no
associated aircraft. Special Condition no. 13, Critical and life-
limited parts, requires magniX to show, by 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. The assumptions
used by magniX in the life-limited parts analysis are design data that
provide information for compliance to Special Condition no. 13. The
installers and operators of the magniX engines do not use these
assumptions, and therefore, the assumptions do not need to be included
in the installation manual. The FAA made no changes to this special
condition as a result of this comment.
Special Condition No. 14, Lubrication System
The FAA proposed that Special Condition no. 14 would require that
the lubrication system of these engines be designed to function
properly between scheduled maintenance intervals and prevent engine
bearing and lubrication system contamination. The FAA also proposed to
require magniX to demonstrate the unique lubrication attributes and
functional capability of the magni350 and magni650 Model engines.
Comment Summary: Wisk recommended removing the reference to
``particle debris'' from Special Condition no. 14(b), and replacing it
with ``The lubrication system must be designed to prevent unacceptable
contamination of the engine bearings.''
FAA Response: The FAA has changed Special Condition no. 14 to
specify the lubrication system must prevent any unacceptable
contamination of the engine bearings. The FAA has changed the special
condition as a result of this comment.
Comment Summary: TCCA recommended that Special Condition no. 14
require magniX to declare, in the engine installation manual, any
reliance upon assumed installation conditions or installation
requirements.
FAA Response: Special Condition no. 1 requires magniX to comply
with14 CFR 33.5, Instruction manual for installing and operating the
engine. Section 33.5(a)(5) includes the additional requirement
recommended by TCCA. The FAA made no changes to the special condition
as a result of the comment.
Special Condition No. 15, Power Response
The FAA proposed that Special Condition no. 15 would require the
design and construction of these engines and their control systems to
enable an increase (1) from the minimum power setting to the highest-
rated power without detrimental engine effects and (2) from the minimum
obtainable power while in-flight and on the ground to the highest-rated
power within a time interval for the safe operation of the aircraft.
Comment Summary: Wisk recommended including the engine control
system as part of the engine in these requirements. They suggest adding
``and its control system'' to this special condition to read, ``The
design and construction of the engine and its control system must
enable an increase.''
FAA Response: The FAA has modified Special Condition no. 15 in
these final special conditions to incorporate ``including its control
system'' in response to the comment.
Comment Summary: Ampaire recommended that the FAA add a requirement
to these special conditions that correspond to ASTM F3338-18, section
5.20.9.
FAA Response: The FAA added Special Condition no. 15(c) in the
final special condition, which incorporates criteria from ASTM F3338-
18, section 5.20.9.
Comment Summary: Textron commented that electrical motors could
produce significantly more torque than reciprocating or turbine
engines. Textron said that unregulated application of torque could be
detrimental to the flight characteristics of the aircraft or the
structural components of the aircraft. Textron recommended
supplementing this special condition with the following requirement:
``(c) of torque without detrimental engine or aircraft effects.
Aircraft components must be designed to withstand the unregulated
application of torque, or the application of torque should be
controlled to ensure aircraft structural integrity or aircraft
aerodynamic characteristics are not exceeded.''
FAA Response: The FAA agrees that electric engines produce torque
differently than turbine engines. The potential for high torque values
is attributable to the novel technology used in magniX's proposed
engines. Therefore, final Special Condition no. 15 has changed to
include a requirement that prevents engine torque from causing
detrimental aircraft effects.
Comment Summary: TCCA recommended that the FAA revise Special
Condition no. 15(b), from ``a time interval for the safe operation of
the aircraft'' to ``a time interval that is determined to be safe for
aircraft operation.''
FAA Response: The FAA finds that the recommended revision would be
beneficial and consistent with the
[[Page 53521]]
change the FAA made to Special Condition no. 10(g) and the addition to
Special Condition no. 17(e), which requires magniX to take into account
the intended aircraft application in the engine installation manual.
The FAA has changed final Special Condition no. 15(b) in the manner
requested by this comment.
Comment Summary: TCCA recommended that the special condition should
state the power-lever movement interval, and that response times in 14
CFR 33.73 should apply to the magniX engines, unless magniX
substantiates different values for the power-lever movement interval
and response times for the aircraft that will use the engines. TCCA
also recommended adapting the existing Sec. 33.73 requirement to
remove the condition only applicable to the turbine engine, such as
surge, stall.
FAA Response: The FAA does not agree with the comment. These
special conditions are applicable only to the magniX engines. Special
Condition no. 10 (Engine control systems) and Special Condition no. 17
(Safety analysis) require magniX to account for the aircraft that can
use these engines. Therefore, the required power-lever movement
interval and response times account for the aircraft safety objectives.
Also, Special Condition no. 15 was developed to be a performance-based
version of Sec. 33.73, so all requirements of Sec. 33.73 are not part
of the special condition. The FAA did not change these special
conditions as a result of this comment.
Special Condition No. 16, Continued Rotation
The FAA proposed that Special Condition no. 16 would prohibit any
hazardous engine effects to result from the continued rotation of
engine rotating systems that the design allows to rotate after the
engine is shut down.
Comment Summary: Textron stated that there is potential for
electric engines to regenerate electric energy from continuing to
freely rotate after the engine is shut down, and recommended an
additional requirement to prevent hazardous electrical bus effects.
FAA Response: These special conditions apply only to the subject
magniX engines, which are not intended to regenerate or otherwise
direct electrical power to the aircraft. The FAA made no changes to the
special condition as a result of the comment.
Special Condition No. 17, Safety Analysis
The FAA proposed that Special Condition no. 17 would require magniX
to comply with 14 CFR 33.75(a)(1), (a)(2), and (a)(3), which require an
applicant to conduct a safety analysis of the engine, and which would
otherwise apply only to applications for turbine aircraft engines.
Additionally, the proposed special conditions would require magniX to
assess its engine design to determine the likely consequences of all
failures that can reasonably be expected to occur, and state, in the
safety analysis, the failure of such elements and associated prescribed
integrity requirements.
As used in Special Condition no. 17, a primary failure is a manner
in which a part fails if the engine is installed in the expected
aircraft configurations and operated in accordance with operating
conditions assumed in the design data such as the expected performance
cycles, engine limits, and operating environments, and maintained using
the declared instructions for continued airworthiness. A primary
failure is not the result of the prior failure of another part or
system.
Some engine parts can fail suddenly in their primary failure from
prolonged exposure to the physical conditions in a normal engine
environment, such as temperature, vibration, and stress. The
probability of failure cannot be sensibly estimated in numerical terms,
and failure will likely result in a hazardous engine effect. As a
result, 14 CFR 33.70, Engine life-limited parts, and 14 CFR 33.75,
Safety analysis, do not allow these parts to be managed by on-condition
or probabilistic means. Therefore, requirements such as life limits,
scheduled inspections, and inspection techniques are mandated to ensure
the essential attributes are preserved throughout the part's service
life. For example, if the number of engine cycles to failure is
predictable and can be associated with specific design characteristics,
such as material properties, then the applicant can manage the engine
part with life limits.
The safety analysis requires magniX to identify hazards that are
applicable to the electric technology used in their engine design. All
the engine hazards that apply to turbine engines also apply to the
magniX electric engines, in addition to possible exceedances of any new
engine limits pursuant to Special Condition no. 2 (Engine ratings and
operating limits) to prevent failure of electronic components that have
a direct impact on safety.
The outcome of the safety analysis partially depends on the
aircraft types that will use these engines. Therefore, final Special
Condition nos. 17(e) and 10(g) require magniX to account for the
intended aircraft application in the engine installation manual to
ensure the magniX engine is installed only in aircraft with compatible
safety assumptions. The term ``intended aircraft application'' means
the aircraft that are expected to operate with the magniX engines.
Comment Summary: Regarding Special Condition no. 17(d)(3), Wisk
recommended that the FAA classify a loss of partial thrust, or a thrust
variation of a small amount, as a ``major effect'' which should be only
considered when the impact is relevant at the aircraft level. Wisk also
stated that the applicable 14 CFR part 23, 25, 27, and 29 regulations
establish appropriate LOTC/LOPC classifications, so a special condition
for 14 CFR 33.75 appears unnecessary. Wisk recommended that Special
Condition no. 17(d)(1) use the existing words of Sec. 33.75(g)(1),
which state, ``An engine failure in which the only consequence is
partial or complete loss of thrust or power (and associated engine
services) from the engine will be regarded as a minor engine effect.''
FAA Response: The FAA does not agree with the comment. These
special conditions are not generally applicable to electric engines.
The requirements only apply to the magniX magni350 and magni650 model
electric engines. The safety analysis classifies engine failures,
including LOTC/LOPC. The classification LOTC/LOPC events partially
depends on the aircraft types that will use these engines, so the
existing engine reliability requirements and accepted partial power
levels in 14 CFR part 23, 25, 27, and 29 aircraft are not directly
applicable without further review of the engine and aircraft
capabilities. In addition, Special Condition no. 10(f)(1) requires the
LOPC rate to be suitable for the intended aircraft application; and
Special Condition no. 10, including 10(f)(2), requires the
Administrator to determine the need for design redundancy relating to
LOPC events to ensure the magniX engine LOPC rate is compatible with
the aircraft safety objectives. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: GE directed attention to the integrity
requirements listed in Special Condition no. 17(b). The requirement
addresses elements (engine parts, components, and systems) that can
fail and are likely to result in hazardous engine effects. GE stated
that the integrity requirements in Special Condition no. 17(b) are not
complete and may not achieve a level of safety equivalent to that
established in 14 CFR 33.75, Safety analysis, and 33.70, Engine life-
limited parts. GE recommended adding a statement that requires magniX
to include any other
[[Page 53522]]
necessary requirements to achieve the safety analysis goals. EASA
provided a similar comment and recommendation.
FAA Response: In response to these comments, the FAA has changed
final Special Condition no. 17(b) to ensure all the applicable
integrity requirements are applied to magniX engine parts that can fail
and are likely to result in hazardous engine effects.
Comment Summary: GE commented that the definitions of ``major'' and
``minor'' engine effects, as mentioned in Special Condition nos.
17(d)(1), 17(d)(2), and 17(d)(3) are ambiguous, leaving a wide gap in
the failure types that could be classified as hazardous or major engine
effects. GE also commented that there is no probability requirement for
major engine effects like there is in 14 CFR 33.75(a)(4). GE
recommended that the FAA clarify the definitions of major and minor
engine effects, and include a probability requirement to ensure a level
of safety commensurate with the current regulations.
FAA Response: These special conditions are not generally applicable
to all electric engines. They apply only to these proposed magniX
engines. The FAA acknowledges many possible outcomes to the engine
safety analysis, including the failure classifications. Failure
classification and probabilities for the engine and certain electronic
components are still needed, but the failure classifications and
reliability thresholds will account for the aircraft's capabilities.
Special Condition no. 17 does not specify the engine failure effects
that could be classified as major because aircraft's capabilities can
affect the failure classification.
As a result of this comment, the FAA modified final Special
Condition nos. 17(d)(1) and 17(d)(3) to clarify the differences between
major and minor engine failure effects. The FAA also added final
Special Condition no. 17(e) to account for the potential influence
aircraft capabilities may have on the engine safety analysis.
Comment Summary: Ampaire recommended adding criteria from the
industry standard ASTM F3338-18, sections 5.18.1 through 5.18.6, to
Special Condition no. 17.
FAA Response: ASTM F3338-18 contains technical criteria that the
FAA incorporated in these special conditions. It also contains
information that the applicant can use to develop a means of compliance
to these special conditions. The FAA did not change these special
conditions as a result of this comment.
Comment Summary: Textron stated that electrical-component
manufacturers typically do not know how their components will be used
or the implications to safety when changes are made to the design and
manufacturing process. Textron recommended modifying Special Condition
no. 17(c) to state: ``In addition, if electrical components of a safety
system are outside the control of the engine manufacturer, then the
manufacturer must implement a component tracking system to monitor
component revisions, change of manufacture, counterfeit parts, and
component end of life (EOL).''
FAA Response: Textron's comment identified a need for engine-level
configuration control. The FAA acknowledges that a product's end-user
could affect the intended engine configuration through parts
manufacturer approvals and supplemental type certificates. However, the
FAA imposed Special Condition no. 1, which mandates magniX's compliance
with14 CFR 33.5(a)(5), 33.5(c), and 33.75 (d) to manage non-OEM engine
configurations. The FAA made no changes to the special condition as a
result of the comment.
Comment Summary: Safran noted that Special Condition no. 17(a)
requires magniX to comply with 14 CFR 33.75(a)(3), which establishes a
fixed numerical value of 10-7 per flight hour for
``extremely remote;'' a number that might exceed the aircraft safety
objectives. For example, ``extremely remote'' for a part 23/Level 1
aircraft application is rated at 10-5 per flight hour, not
10-7. EASA shared Safran's concern and recommended that the
FAA use the EASA SC E-18 \9\ to establish engine safety objectives that
are proportional to the safety objectives of the intended aircraft when
they are equipped with the magniX engines.
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\9\ https://www.easa.europa.eu/sites/default/files/dfu/sc_e-18_electric_propulsion_units_for_cs-23_normal-category_aeroplanes_u.pdf.
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FAA Response: Both comments presume the general applicability of
the proposed special conditions. These special conditions apply only to
magniX's two proposed engine models. The aircraft that will use the
magniX engines do not include Part 23/Level 1 aircraft. However, the
FAA acknowledges that acceptable engine failure rates could vary
depending on the aircraft's configuration and capabilities. Therefore,
the FAA removed reference to Sec. 33.75(a)(3) from Special Condition
no. 17(a). Also, The FAA changed final Special Condition no. 10(g) and
added Special Condition no. 17(e) to require magniX to account for the
intended aircraft application.
Comment Summary: TCCA stated the term ``electrocution'' is defined
as ``to kill with electricity'' and recommended that the FAA change the
term ``electrocution'' in this special condition to ``electric shock''
or ``injury from electric shock.''
FAA Response: The FAA does not agree with the comment. The term
``electrocution,'' as used in these special conditions, is consistent
with the risk of serious injury or fatality caused by electric shock.
Comment Summary: TCCA asked the FAA to explain why proposed Special
Condition no. 17 did not include the requirement for major failure
rates in 14 CFR 33.75(a)(4).
FAA Response: To account for the potential dependency between the
electric engine safety analysis and the aircraft capabilities, the FAA
did not prescribe failure rates for major engine failures. Special
Condition no. 10(g) and Special Condition no. 17(e) require magniX to
account for the intended aircraft application. magniX will still need
to classify major failures for the engine and certain electronic
components, but the failure rates will account for aircraft
capabilities. The FAA has changed the special condition as a result of
this comment.
Comment Summary: TCCA asked the FAA to consider requiring the
applicant's safety analysis to analyze uncontrollable high thrust and
potential physical separation of the engine from the aircraft.
FAA Response: The FAA understands TCCA's reference to
``uncontrollable'' high thrust to mean a higher thrust than the
commanded thrust or a thrust that is above a limit value. Special
Condition no. 10(f)(1) requires a maximum LOPC rate for the intended
aircraft that will use the magniX engines, and magniX will need to show
how they comply with those rates. Special Condition no. 17(d)(2)
requires magniX to comply with 14 CFR 33.75(g)(2)(v), which addresses
the physical separation of the engine from the aircraft. The FAA did
not change this special condition as a result of this comment.
Comment Summary: TCCA suggested that the FAA require magniX to show
that a cooling loss will not result in a hazardous engine effect or
that blockage cannot lead to a cooling failure. TCCA's comment was
directed to Special Condition no. 18 in the context of protecting the
cooling inlet from ingestion.
FAA Response: In response to TCCA's comment, the FAA has included a
requirement in Special Condition no.
[[Page 53523]]
17(d)(2)(ii) to prevent hazardous engine effects from cooling blockage.
Comment Summary: EASA commented that the special condition has no
proposed safety objectives for major failure conditions. EASA
recommended that the FAA use the approach of EASA SC E-19 \10\ that
requires the propulsion system to have a level of safety that allows
the intended aircraft to meet its safety objectives defined in the
aircraft type certification basis.
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\10\ https://www.easa.europa.eu/document-library/product-certification-consultations/final-special-condition-sc-e-19-electric.
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FAA Response: There are many possible outcomes to the magniX engine
safety analysis, including the failure classifications. Failure
classification and probabilities for the engine and certain electronic
components are needed, but the failure classifications and reliability
thresholds will account for aircraft capabilities. The FAA has changed
final Special Condition no. 10(g) and added Special Condition no. 17(e)
to require magniX to account for the intended aircraft application.
The additions to Special Condition nos. 10(g) and 17(e) allow for
the aircraft safety objectives to be considered when establishing the
engine failure classifications and failure rates.
Comment Summary: EASA noted the reference to Special Condition no.
9 in Special Condition no. 17(b): ``If the failure of such elements is
likely to result in hazardous engine effects, then the applicant may
show compliance by reliance on the prescribed integrity requirements of
14 CFR 33.15, Special Condition no. 9, or Special Condition no. 13, as
determined by analysis.''
EASA stated that proposed Special Condition no. 9 is insufficient
for hazardous failure conditions. EASA said that a rotor growth margin
is a design margin, but it does not preclude any other failure root
cause of a failure, such as a production issue. EASA suggested that the
FAA change these special conditions to remove this possibility.
FAA Response: The FAA agrees with the comment. There might be a
need to consider additional integrity requirements to account for the
potential root causes for failures of the magniX electric engine parts.
The FAA has changed final Special Condition 17(b) to add ``such as''
before the list of integrity requirements.
Special Condition No. 18, Ingestion
The FAA proposed that Special Condition no. 18 would require magniX
to ensure that these engines will not experience unacceptable power
loss or hazardous engine effects from ingestion. For example, the
current bird-ingestion airworthiness regulation for turbine engines, 14
CFR 33.76, is based on potential damage from birds entering a turbine
engine with an inlet duct that directs air into the engine for
combustion, cooling, and thrust. In contrast, these electric engines do
not use an inlet duct for those purposes. Instead, the electric engine
inlet duct is primarily used to streamline the air entering the inlet
for efficient cooling of internal engine components.
An ``unacceptable'' power loss, as stated in Special Condition no.
18(a), refers to a situation in which the power or thrust required for
safe flight of the aircraft becomes unavailable to the pilot. The
specific amount of power loss necessary for a safe flight depends on
the aircraft configuration, speed, altitude, attitude, atmospheric
conditions, phase of flight, and other circumstances, where the demand
for thrust is critical to the aircraft's safe operation.
This special condition also requires magniX to declare the
ingestion sources that are not evaluated in the engine installation
manual.
Comment Summary: Textron recommended that this special condition
quantify the ingestion threats in a manner similar to the way they are
quantified for turbine engines in 14 CFR 33.76, Bird ingestion, Sec.
33.77, Foreign object ingestion--ice, and Sec. 33.78, Rain and hail
ingestion. The commenter suggested that bird numbers and sizes, ice,
rain, and hail concentrations should be provided.
FAA Response: The FAA does not agree with Textron's recommendation.
A special condition is not required to quantify ingestion threats. The
FAA did not change this special condition as a result of this comment.
Comment Summary: Airbus stated that while detailed means of
compliance (test, analysis, etc.) need not be part of this special
condition, the FAA should specify the ingestion conditions, such as
icing environments, that magniX must consider in showing compliance.
FAA Response: The FAA has changed final Special Condition no. 18 to
require ingestion sources, that are not evaluated by magniX, to be
declared in the engine installation manual.
Comment Summary: Textron recommended that this special condition
include a provision to prevent the accumulation of ferromagnetic
material in the air-cooled passages, and to prevent blockages and short
circuits between the rotor and the stator for non-sealed engines.
FAA Response: The FAA does not agree with this comment. The special
condition requires magniX to consider ingestion of material originating
from outside the engine, not from within it. The potential for
ferromagnetic contamination of engine bearings from sources within the
engine would not likely meet the requirements established in these
special conditions, such as Special Condition nos. 5 (Durability) and 7
(Safety Analysis). The contamination is more likely a consequence of an
engine failure or inadequate maintenance. The FAA made no changes to
these special conditions as a result of this comment.
Comment Summary: EASA stated rain conditions are a normal flight
condition, even in VFR, and should be distinguished from other
ingestion phenomena. EASA recommended incorporating EASA Special
Condition E-18 issue 2: ``operation under rain conditions must not
result in any abnormal operation (i.e., shutdown, power loss, erratic
operation, power oscillations, failures . . .) throughout the EPU
operating range.''
FAA Response: The FAA has modified Special Condition no. 18 in
response to this comment to require the magniX engine to operate safely
in rain environments. The word ``rain'' was removed from Special
Condition no. 18(a). The following special conditions were added:
Special Condition no. 18(b), which provides that rain ingestion must
not result in an abnormal operation such as shutdown, power loss,
erratic operation, or power oscillations throughout the engine
operating range, and Special Condition no. 18(d), which requires the
applicant to declare, in the engine installation manual, ingestion
sources that are not evaluated.
Comment Summary: EASA asked the FAA to verify the proposed Special
Condition no. 18 might result in a limitation that could be established
at the aircraft-level for operation in icing conditions.
FAA Response: These special conditions are not intended for all
electric engine certification projects. They are intended for the
magni350 and magni650 electric engines. magniX intends to pursue a type
certificate for their electric engine. If magniX elects to omit likely
sources of ingestion (foreign objects, birds, ice, hail) from their
evaluations, Special Condition no. 18(d) requires magniX to declare
ingestion sources that are not evaluated in the engine installation
manual, except for rain. Special Condition no. 18(b) was added as a
result of EASA's comment to implement performance requirements in
[[Page 53524]]
rain conditions. No changes were made to this special condition as a
result of this comment.
Special Condition No. 19, Liquid Systems
The FAA proposed that Special Condition no. 19 would require magniX
to ensure that liquid systems used for lubrication or cooling of engine
components are designed and constructed to function properly. Also, the
FAA proposed that, if a magniX engine liquid system is shared with an
aircraft liquid system, the interfaces between the engine and aircraft
systems must be defined in the engine installation manual.
Comment Summary: Wisk recommended that these special conditions
address the risk of a liquid system freezing after an engine shutdown
and preserve the ability for engine restart.
FAA Response: These special conditions already account for the
concerns expressed by Wisk. Special Condition no. 19 requires magniX to
ensure the liquid system operates appropriately in all atmospheric
conditions in which the engine is expected to operate. The FAA did not
change Special Condition no. 19 as a result of this comment.
Comment Summary: Rolls-Royce noted that the FAA did not propose to
require the design to comply with 14 CFR 33.64, Pressurized engine
static parts. The commenter stated that it anticipated electric engine
configurations with pressurized cooling systems and pressurized
lubrication systems and recommended that this requirement be included
in these special conditions.
FAA Response: These special conditions are not generally applicable
to all electric engines and apply only to these proposed magniX
electric engines. However, magniX may choose to pressurize the liquid
systems in their engines. Therefore, the FAA has changed final Special
Condition no. 19 to require magniX to account for pressurized static
engine parts.
Comment Summary: Textron recommended that these special conditions
require that the engine installation manual prescribe the cooling and
lubricating fluids used on these engines.
FAA Response: The FAA has modified Special Condition no. 19 in
these final special conditions to require magniX to list eligible
lubricants and coolants in the engine installation manual.
Comment Summary: Textron recommended that the FAA add a requirement
that prevents magnetically attracted engine debris from accumulating in
passages that could block or limit coolant flow.
FAA Response: The potential for magnetic debris in the magniX
engine liquid cooling system would likely be a consequence of an engine
failure or inadequate maintenance. If this were a characteristic of the
type design, the magniX engines would not likely meet the requirements
established in these special conditions, such as Special Condition nos.
5 (Durability) and 7 (Safety Analysis). The FAA did not change Special
Condition no. 19 as a result of this comment.
Comment Summary: TCCA noted the possibility that the magniX
electric engine liquid system might rely on aircraft systems. In that
case, TCCA recommended that these special conditions require that
reliance be declared in the engine installation manual.
FAA Response: Special Condition no. 1 requires magniX to comply
with 14 CFR 33.5, Instruction manual for installing and operating the
engine. The requirements in Sec. Sec. 33.5(a)(5) and 33.5(c) address
the safety concern raised in this comment. The FAA did not change
Special Condition no. 19 due to this comment.
Special Condition No. 20, Vibration Demonstration
The FAA proposed that Special Condition no. 20 would require magniX
to ensure (1) the engine is designed and constructed to function
throughout its normal operating range of rotor speeds and engine output
power without inducing excessive stress caused by engine vibration, and
(2) the engine design undergoes a vibration survey.
Comment Summary: Wisk recommended that the FAA incorporate the
requirements from 14 CFR 33.83(f), Vibration test, instead of proposed
Special Condition no. 20(b), when the installation can be assessed by
analysis to match an approved engine installation because the existing
14 CFR part 33 regulation does not appear to require a vibration
survey.
FAA Response: This special condition combines the requirements of
Sec. Sec. 33.63, Vibration, and 33.83, Vibration test. Special
Condition no. 20(a) corresponds to Sec. 33.63, Subpart E, which has
provisions for the design and construction of the electric engine.
Special Condition no. 20(b) corresponds to Sec. 33.83, Subpart F,
which applies to the block tests. This Sec. 33.83, Vibration test,
reference explains why a vibration survey is specified in Special
Condition no. 20(b) and not in 20(a). In addition, the special
condition requires magniX engines to undergo a vibration survey using
test, validated analysis, or a combination of both. Therefore, this
special condition addresses Wisk's comment. The FAA did not change this
special condition as a result of this comment.
Comment Summary: Ampaire suggested the terminology used in the
title of proposed Special Condition no. 20 described a ``vibration
demonstration,'' and the term used in the ASTM document referred to the
requirement as a ``test'' (ref. ASTM F3338-18, section 5.20.4).
FAA Response: A demonstration is a test, but this special condition
also allows validated analysis to show compliance. A test is required
to validate an analysis, so the requirement is grounded in a test. The
FAA did not change this special condition as a result of this comment.
Comment Summary: TCCA stated that paragraph (a) of proposed Special
Condition no. 20 is similar to 14 CFR 33.83(b), which has a
demonstration element. TCCA asked that the FAA clarify when to use
representative propeller loads during engine testing. TCCA also
recommended the FAA add clarification within Special Condition no. 20
to explain when propeller loads are required during the engine
demonstrations.
FAA Response: Special Condition no. 20 has a demonstration element.
Special Condition no. 20(a) corresponds to 14 CFR 33.63 in Subpart E,
Design and Construction; Turbine Aircraft Engines, and Special
Condition no. 20(b) corresponds to Sec. 33.83 in Subpart F, Block
Tests; Turbine Aircraft Engines. TCCA's comment also relates to Special
Condition no. 31, Operation with a variable pitch propeller, which
corresponds to Sec. 33.95, Engine-propeller systems tests. As a result
of TCCA's comment, the FAA modified final Special Condition no. 31 to
enable magniX to run their engines with a variable pitch propeller
during the operation demonstration.
Comment Summary: TCCA recommended that the FAA add a requirement
for magniX to evaluate the vibration effects from sustained engine
unbalance to protect the engine and aircraft from vibration effects
caused by engine failures that result in windmilling or propeller pitch
or propeller feathering issues. TCCA recommended adding a paragraph
that states, ``The effects on vibration characteristics of excitation
forces caused by fault conditions must be evaluated by test or
analysis, or by reference to previous experience and
[[Page 53525]]
shown not to result in a hazardous engine effect.''
FAA Response: Special Condition no. 16 (Continued rotation)
corresponds to 14 CFR 33.74, which precludes hazardous engine effects
from continued rotation of engine main rotating systems after the
engine is shut down for any reason while in flight. This includes the
effects of vibration from failures that result in a rotor unbalance.
Therefore, Special Condition no. 16 addresses the failure effects TCCA
identified in their comment. The FAA did not change these special
conditions as a result of this comment.
Comment Summary: TCCA recommended requiring an evaluation of
vibration effects that result from excitation forces caused by fault
conditions or to address these effects by reference to experience with
engine failures that did not result in a hazardous engine effect. TCCA
also recommended addressing the vibration effects from sustained engine
unbalance.
FAA Response: Special Condition no. 16 (Continued rotation)
precludes hazardous engine effects from continued rotation after the
engine is shut down for any reason while in flight, including fault
conditions. These special conditions are applicable to the magniX
engines, which are new to aviation. Therefore, engine experience is not
relevant to the magniX engine certification project. The FAA did not
change this special condition as a result of this comment.
Special Condition No. 21, Overtorque
The FAA proposed that Special Condition no. 21 would require magniX
to demonstrate that the engine is capable of continuous operation
without the need for maintenance if it experiences a certain amount of
overtorque.
Comment Summary: TCCA suggested that the FAA add the teardown
inspection requirement of Special Condition no. 29 for each engine part
or individual groups of components after conducting the overtorque
test.
FAA Response: The additional requirement suggested by TCCA
corresponds to 14 CFR 33.84(a)(2), Engine overtorque test. The engines
proposed by magniX may require a transient maximum overtorque rating.
The FAA has changed final Special Condition no. 21 to require
compliance to Special Condition no. 29 (Teardown inspection) after
conducting an overtorque test.
Special Condition No. 22, Calibration Assurance
The FAA received no comments for Special Condition no. 22, and it
is adopted as proposed. It requires magniX to subject the engine to
calibration tests, to establish its power characteristics and the
conditions both before and after the endurance and durability
demonstrations specified in proposed Special Condition nos. 23 and 26.
The calibration test requirements specified in Sec. 33.85 only apply
to the endurance test specified in Sec. 33.87, which is applicable
only to turbine engines. The methods used for accomplishing those tests
for turbine engines are not the best approach for electric engines. The
calibration tests in Sec. 33.85 have provisions applicable to ratings
that are not relevant to the magniX magni350 and magni650 model
engines. Special Condition no. 22 allows magniX to demonstrate the
endurance and durability of the electric engine either together or
independently, whichever is most appropriate for the engine qualities
being assessed. Consequently, this special condition applies the
calibration requirement to both the endurance and durability tests.
Special Condition No. 23, Endurance Demonstration
The FAA proposed that Special Condition no. 23 would require magniX
to subject the engine to an endurance demonstration test, acceptable to
the Administrator, to demonstrate the engine capabilities at the
declared limits.
The FAA proposed to evaluate the extent to which the test exposes
the engine to failures that could occur when the engine is operated at
its rated values, to determine if the test is sufficient to show that
the engine design will not exhibit unacceptable effects in-service,
such as significant performance deterioration, operability
restrictions, and engine power loss or instability, when run for
sustained periods at extreme operating conditions.
Comment Summary: Rolls-Royce stated that the second sentence of the
proposed special condition contained a typographical error and
suggested that it should read, ``The endurance demonstration elevates
and increases the engine's power settings, and dwells at the power
settings for durations that produce the extreme physical conditions. .
. .'' Rolls-Royce recommended replacing ``decreases'' with
``increases'' in the special condition.
FAA Response: Final Special Condition no. 23 has been changed. The
FAA considered the change proposed by Rolls-Royce and changed the term
``elevates'' to ``increases.''
Comment Summary: TCCA recommended that the FAA add the following
three sentences to Special Condition no. 23: (1) ``The severity of the
demonstration should consider the design and intended use of the
engine, and include the demonstration of safe operation under all
operational limits to be applied during service operation of the
engine.'' (2) ``When approval is sought for Normal Transient engine
exceedances, it must be substantiated that the engine is capable of
operation at the maximum engine transient condition of the affected
engine parameter(s) without maintenance action.'' (3) ``When approval
is sought for Inadvertent Transient engine exceedances, it must be
substantiated that the engine is capable of operation at the maximum
engine transient condition of the affected engine parameter(s) without
maintenance action other than to correct any failure that led to the
exceedances.''
FAA Response: The FAA does not agree to include the additions
recommended by TCCA. Regarding TCCA sentence (1), adding a definition
for severity in this special condition is unnecessary because this
special condition is intended to achieve the same objectives as 14 CFR
33.87, Endurance test, but for the magniX electric engines. The test
will be different for the magniX engines because those engines use
electrical technology for propulsion. Whether the engine is turbine or
electric, the endurance test achieves a severity that demonstrates the
engine is safe to operate at its certificated limits.
Regarding TCCA sentence (2), Special Condition no. 32 requires the
engine and its components to be within serviceable limits, safe for
continued operation, and capable of operating at declared ratings while
remaining within limits upon completing all demonstrations and testing
specified in these special conditions. If the magniX engine ratings
include maximum transients, the engines must demonstrate that they
operate safely during the maximum transients and meet the post-test
engine requirements specified in these special conditions.
Regarding TCCA sentence (3), Special Condition no. 23 is intended
to assess the magniX engine's capabilities. It is not intended to show
the engine can accommodate failures and malfunctions that lead to
inadvertent transients that exceed the engine's certificated limits.
Special Condition no. 17 (Safety analysis) addresses potential effects
[[Page 53526]]
from exceeding maximum limits and transients. Results from the safety
analysis are used to decide how to manage the consequences of all
failures that can reasonably be expected to occur.
Special Condition No. 24, Temperature Limit
The FAA proposed that Special Condition no. 24 would require magniX
to ensure the engine can endure operation at its temperature limits,
plus an acceptable margin. An ``acceptable margin,'' as used in this
special condition, is the amount of temperature above that required to
prevent the least-capable engine allowed by the type design from
failing due to temperature-related causes when operating at the most
extreme thermal conditions.
Comment Summary: Textron recommended that the FAA require the
applicant to consider environmental conditions and that the engine
temperature limit be substantiated at the worst-case environmental
conditions to ensure the engine cooling system performance is adequate
when the engine operates at the declared temperature limit.
FAA Response: The FAA has changed final Special Condition no. 24
with a requirement for magniX to account for operating environments
when they establish a value for the engine temperature limit.
Comment Summary: TCCA recommended that Special Condition no. 24
include the following footnote: ``Acceptable margin, as used in the
proposed special condition, is the amount of temperature above that
required to prevent the least-capable engine allowed by the type design
from failing due to temperature-related causes when operating at the
most extreme thermal conditions.'' TCCA also recommended that Special
Condition no. 24 includes: ``Upon completion of the demonstration, the
engine must be within serviceable limits.''
FAA Response: The FAA does not agree with this comment. The
following special conditions already incorporate the technical criteria
proposed by TCCA:
Special Condition no. 1 requires magniX to comply with 14 CFR 33.8,
Selection of engine power and thrust ratings, for the proposed engines.
Section 33.8(b) requires that each selected rating must be for the
lowest power or thrust that all engines of the same type may be
expected to produce under the conditions used to determine that rating.
This requirement will address the temperature margins required for the
least (thermally) capable engine the type design allows.
Special Condition no. 32(c) (General conduct of tests) has
provisions that require the engine and its components to be within
serviceable limits, safe for continued operation, and capable of
operating at the declared ratings without exceeding limits after
completing the tests identified in these special conditions.
Special Condition no. 24 requires the engine design to demonstrate
its capability to endure operation at its temperature limit plus an
acceptable margin.
Special Condition no. 12 (Stress analysis) includes a requirement
for a thermal stress analysis to show a sufficient design margin to
prevent unacceptable operating characteristics and hazardous engine
effects.
Therefore, Special Condition nos. 12, 24, 32(c), and Sec. 33.8
address TCCA's recommendation. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: EASA commented that the temperature limit is a new
requirement compared to the requirements in 14 CFR part 33, EASA CS-
E's,\11\ and the technical criteria in ASTM F3338-18. EASA stated that
the applicant demonstrates operation up to the limits as part of the
endurance test. EASA further commented that the engine's serviceability
after the endurance test is sufficient proof that the engine has been
designed and manufactured with margins compared to the limits declared
in the engine installation manual. Therefore EASA recommended removing
this requirement from this special condition.
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FAA Response: The FAA does not agree with this comment. The FAA
included a temperature limit because it is directly related to a
primary failure mechanism associated with the novel technology used in
magniX's proposed electric engine designs. The FAA did not change this
special condition as a result of this comment.
Special Condition No. 25, Operation Demonstration
The FAA proposed that Special Condition no. 25 would require that
the engine demonstrate safe operating characteristics throughout its
declared flight envelope and operating range. The engine performance
data magniX will use to certify each engine must account for
installation loads and effects.
Comment Summary: Ampaire stated that the terminology used in the
proposed special condition uses the term ``demonstration,'' and the
term used in the ASTM document refers to the requirement as a ``test''
(ref. ASTM F3338-18, section 5.20.8).
FAA Response: As used in these special conditions, a demonstration
is a test, but the special condition also allows validated analysis to
show compliance. A test is required to validate an analysis, so the
requirement is always grounded in a test. The FAA made no changes to
the special condition as a result of this comment.
Comment Summary: Ampaire suggested that in-flight restart
characteristics are a critical capability of electric engines and
recommended that the FAA require this capability as part of the engine
demonstration test. Airbus and TCCA also recommended that the FAA
require a demonstration of in-flight restart capability. In addition,
TCCA recommended that the special conditions require these
demonstrations to be conducted with a representative propeller.
FAA Response: The FAA does not agree with the comments. Engine in-
flight restart capabilities are established at the aircraft level in
accordance with 14 CFR 23.2425(b), 25.903(e), 27.903(d), and 29.903(e).
These regulations also require installed engines to have a restart
capability within the aircraft's flight envelope. Therefore, a
requirement for magniX to verify the in-flight restart capability of
their engines during the engine certification program is not within the
bounds of these special conditions. No changes were made to final
Special Condition no. 25 as a result of this comment.
Comment Summary: TCCA asked if a gearbox assembly is considered as
a single ``part'' of the engine.
FAA Response: A gearbox assembly is not considered to be a single
part of the magniX engine. Gearboxes used in the magniX engines are
treated as an engine accessory. The 14 CFR part 33 requirements imposed
by Special Condition no. 1 that address engines with gearboxes and
apply to magniX engines are 14 CFR 33.3, 33.5, 33.25, and Appendix
A33.3. The special conditions that correspond to 14 CFR part 33
requirements that address gearboxes used in the magniX engines are
Special Condition nos. 2, 15, 20, 22, 23 and 26. No changes were made
to these special conditions as a result of TCCA's comment.
Special Condition No. 26, Durability Demonstration
The FAA proposed that Special Condition no. 26 would require magniX
to subject the engine to a durability
[[Page 53527]]
demonstration. The durability demonstration must show that each part of
the engine is 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.
Comment Summary: TCCA commented that these special conditions do
not contain a modified 14 CFR 33.4 description of ICA for the intended
electric engine applications. TCCA suggested that ICA should represent
all the instructions required for the magniX engines to remain
airworthy, but that instructions for off-wing maintenance instructions
in the ICA would not be appropriate.
FAA Response: These special conditions are not intended for all
electric engine certification projects. As required by Special
Condition no. 1, magniX must comply with Sec. 33.4, Instructions for
Continued Airworthiness, and its appendix. These requirements are
appropriate to address the maintenance requirements for these proposed
engine designs. The FAA made no changes to the special condition as a
result of the comment.
Comment Summary: TCCA recommended adding 14 CFR 33.19(b), Propeller
pitch control design requirements, to Special Condition no. 26, with an
opt-out option if the magniX engines do not have propeller-blade pitch
control systems.
FAA Response: These special conditions apply to the magni350 and
magni650 model engines. These magniX engines do not have a propeller-
blade pitch control system. The FAA made no changes to the special
condition as a result of the comment.
Comment Summary: TCCA recommended revising this special condition
to state, ``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 and subsystem between
overhaul periods or between engine components/parts replacement
intervals. . . .''
FAA Response: magniX's proposed engines must meet Special Condition
no. 29 (Teardown inspection) requirements after completing the
durability demonstration specified in this special condition. In
addition, magniX must meet the requirements of Special Condition no. 32
(General conduct of tests). These special conditions, in combination
with the demonstration tests required by these magniX special
conditions, achieve the objectives identified by this comment. The FAA
made no changes to the special condition as a result of the comment.
Comment Summary: TCCA suggested that the FAA modify Special
Condition no. 26 in a manner that results in the following revision:
``This test must simulate the conditions in which the engine is
expected to operate in-service, including typical start-stop cycles and
scheduled maintenance actions and must be of sufficient duration in
order to provide confidence in the durability of the engine.''
FAA Response: The FAA does not agree with the comment. The required
durability demonstration provides information for compliance to 14 CFR
33.4, Instructions for continued airworthiness, which is imposed by
Special Condition no. 1. If maintenance is required to complete the
test, the specific maintenance actions could become part of the
mandatory ICA. The discussion for Special Condition no. 32 contains
more information about maintenance conducted during a test. Special
Condition no. 32 (General conduct of tests) has criteria that permit
some maintenance to be accomplished during the test without incurring
additional mandatory ICA. The FAA agrees that the test duration can
provide confidence in the engine's durability. However, whether the
test duration is long or short, magniX will develop a maintenance plan
based on the test that magniX creates for their program, in accordance
with Sec. 33.4. The FAA made no changes to the special condition as a
result of the comment.
Special Condition No. 27, System and Component Tests
The FAA proposed that Special Condition no. 27 would require magniX
to show that the engine's systems and components would perform their
intended functions in all declared engine environments and operating
conditions.
Comment Summary: TCCA recommended that the FAA require magniX to
establish temperature limits for each component that requires
temperature-controlling provisions in the aircraft installation to
assure satisfactory functioning, reliability, and durability.
FAA Response: Other special conditions address TCCA's concern.
Special Condition no. 2 (Engine ratings and operating limits) requires
magniX to establish a temperature limit that is necessary for safe
operation of the engine. Whether or not a temperature limit is
established for a component depends on the outcome of Special Condition
no. 17 (Safety analysis), which examines the consequence of engine
failure from high-temperature. If cooling is required to satisfy
Special Condition no. 17 (Safety analysis), the cooling system
monitoring features and usage are documented in accordance with Sec.
33.5(c), Safety analysis instructions. The FAA did not change this
special condition as a result of this comment.
Comment Summary: TCCA recommended that the FAA require magniX to
establish voltage and current limits ``for each component that requires
voltage or current controlling provisions, or both, in the aircraft
installation to assure satisfactory functioning, reliability, and
durability.''
FAA Response: Other special conditions address TCCA's concern.
Regarding voltage and current limits, Special Condition no. 2 requires
magniX to establish ratings and operating limitations based on power-
supply requirements for the engine. Whether or not voltage and current
limits are established for a component depends on the outcome of
Special Condition no. 17 (Safety analysis), which examines the
consequence of the component's failure from high temperature. The FAA
did not change this special condition as a result of this comment.
Special Condition No. 28, Rotor Locking Demonstration
The FAA proposed that Special Condition no. 28 would require the
engine to demonstrate reliable rotor locking performance and that no
hazardous engine effects will occur if the engine uses a rotor locking
device to prevent shaft rotation.
Comment Summary: Wisk stated that this special condition does not
contain a requirement that ensures the rotor lock feature cannot be
enabled with a motor power set and also that its inadvertent activation
is sufficiently unlikely that no major engine effect can occur. Wisk
recommended that the FAA clarify if the term ``hazardous'' is being
used in the context of system safety or in general terms.
Textron also requested that the FAA clarify the definition of
``hazardous effects'' and use that term consistently and recommended
the following be added to Special Condition no. 28: ``. . . that no
hazardous effects as specified in Special Condition no. 17(d)(2) will
occur.''
FAA Response: If magniX implements a rotor locking device in their
engine design, Special Condition no. 28 will ensure the device exhibits
reliable rotor locking performance and will not cause hazardous engine
effects to preserve system safety. Special Condition no. 17 (Safety
analysis) examines the
[[Page 53528]]
consequence of accidental rotor locking while the aircraft is in-flight
and classifies the failure as either hazardous or major. The magniX
engine will need to meet the requirements of this special condition and
those of the safety analysis, which provide protection from inadvertent
rotor locking.
The FAA clarified the terms ``hazardous'' and ``hazardous engine
effects'' as they are used in Special Condition no. 28 by adding a
reference to Special Condition no. 17(d)(2). The FAA changed final
Special Condition no. 28 as a result of this comment.
Comment Summary: Textron requested that Special Condition no. 28
require magniX to consider the potential hazards from an automatic
rotor locking system. Textron stated that if the engine is shut down
during flight, and the locking device is automatic, the flight crew
needs to have a means to remove the locking device and restart the
engine without creating a hazard. The commenter recommended adding the
following to Special Condition no. 28: ``(b) When the locking device is
in place, an indication shall be provided so that the crew will be able
to retract the device while in flight.''
FAA Response: The FAA does not agree with the comment. magniX
verifies rotor lock performance and reliability using the tests
required by Special Condition no. 28. Typically, only rotorcraft have
cockpit indications for locking devices. Those rotorcraft cockpit
indications for locking devices are for main rotor transmissions, which
are aircraft-level components. If an engine lock position indication is
required to meet the aircraft safety objectives, the devices that
notify the crew are part of the aircraft safety system. The FAA did not
change these special conditions as a result of this comment.
Comment Summary: TCCA commented that this special condition should
allow additional techniques to verify rotor locking performance. TCCA
also suggested that the special condition requires a demonstration of
reliable rotor ``unlocking'' performance.
FAA Response: Final Special Condition no. 28 has been changed to
add rotor unlocking performance to the demonstration. However, allowing
the use of a validated analysis would render the demonstration
optional.
Special Condition No. 29, Teardown Inspection
The FAA proposed that Special Condition no. 29 would require magniX
to perform either a teardown evaluation or a non-teardown evaluation
based on the criteria of Special Condition no. 29(a) or (b).
The FAA proposed that Special Condition no. 29(a) would require
that the engine be disassembled after the endurance and durability
demonstrations to verify each component remained within its service
limits and in a condition for continued operation in accordance with
Sec. 33.4, Instructions for Continued Airworthiness.
The FAA proposed that Special Condition no. 29(b) would require
magniX, for ``non-teardown evaluations,'' to establish life limits
based on endurance and durability demonstrations.
In final Special Condition no. 29(b), magniX is required, for non-
teardown evaluations, to account for engines, sub-assemblies, and
components that cannot be disassembled without destroying the
components. If teardown and inspection are not accomplished for
components or assemblies after testing, the maintenance requirements
for the engine are contingent on the demonstrated capabilities
exhibited during the certification tests.
Comment Summary: GE recommended that the FAA clarify how life
limits will be established if magniX cannot complete the teardown
inspection of parts or components after the endurance and durability
demonstrations. GE stated that the life limits should be documented in
the engine's airworthiness limitations or the engine's ICA. TCCA also
requested clarification about how life limits are established for parts
and components that are not torn down after testing.
FAA Response: Special Condition no. 29 can have an effect on life
limits. In the foregoing discussion of this condition, the FAA provided
additional information to clarify how maintenance (such as life limits)
is established for parts and components that are not torn down and
inspected after testing. Also, the FAA changed final Special Condition
no. 29 to require life limits resulting from this special condition to
be documented in the ICA, in accordance with 14 CFR 33.4.
Comment Summary: Textron recommended that the FAA require
inspections of electrical components in the controller after the
endurance and durability demonstrations. Textron stated that, at a
minimum, the FAA should require inspection of the controller's
fasteners, heat transfer components, dissimilar metallic junctions, and
age or use affected electrical components.
FAA Response: The preamble of these special conditions explains
that the magniX engine consists of an electric motor, controller, and
high-voltage systems. Special Condition no. 29(a) requires the engine
to be completely torn down and inspected. Special Condition no. 29(b)
contains provisions for engine components that are not disassembled for
inspection. The FAA did not change these special conditions as a result
of this comment.
Comment Summary: An individual commenter suggested potential long-
term issues with main bearing lubrication related to grease life. The
commenter stated that these issues might not be evident after
completing a certification program.
FAA Response: In response to this comment, the FAA has changed
final Special Condition no. 29(b) to require a life limit for the
bearing lubricant if the bearing is not disassembled after testing. The
FAA has changed the special condition as a result of this comment.
Comment Summary: TCCA recommended that the FAA mandate additional
tests if the teardown inspection shows that part replacement is
necessary.
FAA Response: The FAA does not concur with the comment. Special
Condition nos. 32(b) and (b)(4) (General conduct of tests) already have
the requested provisions for additional testing of parts that require
replacement during a test or based on their condition at teardown
inspection. The FAA made no changes to the special condition as a
result of the comment.
Comment Summary: EASA commented that this Special Condition no.
29(b) was proposed to define the life limits of the tested components
based on the endurance and durability tests. EASA stated this special
condition was not aligned with ASTM F3338-18 and asked the FAA to
elaborate on whether the selected limit is the highest or lowest one
and how limits are compared if they are based on different test
conditions.
FAA Response: ASTM F3338-18, section 5.22.1.5 establishes life
limits for an electric engine based on the length of an endurance test
if the engine is not torn down for inspection after the test. These
special conditions require individual life limits to be established,
based on endurance and durability demonstrations if individual
components are not torn down and inspected after the tests. This
special condition is consistent with the ASTM document EASA referenced
in their comment. Because these special conditions apply to the magniX
engine, the life limits will be based on the test conditions magniX
uses to assess their engines. The FAA made no changes to
[[Page 53529]]
the special condition as a result of the comment.
Comment Summary: TCCA recommended that Special Condition no. 29
apply the non-teardown requirement to those components that need
additional testing in accordance with Sec. Sec. 33.53(a), Engine
system and component tests or 33.91(a), Engine system and component
tests. TCCA commented that, as the special condition is currently
worded, some might apply the requirement only to internal engine parts.
TCCA also requested that the FAA modify the special condition to
require some post-test assessments for non-torn down components. TCCA
also asked that the FAA clarify the requirement that ``then the life
limits for these components must be established based on the endurance
and durability demonstrations.'' TCCA contended that, as this
requirement is currently worded, magniX could interpret it to mean that
all internal parts of the electric engine would not need to be
examined, including (Non-Destructive Testing) NDT, especially if there
is no overhaul.
FAA Response: Special Condition no. 27 ensures that magniX
addresses electric engine components that cannot be torn down for
inspection. If the condition of these parts is questionable, then the
requirements in Special Condition nos. 32(b) and 32(b)(4) can be
applied for additional data to substantiate the life limit. These
special conditions address TCCA's comments. The FAA did not change the
special condition as a result of this comment.
Special Condition No. 30, Containment
The FAA proposed that Special Condition no. 30 would require the
engine to provide containment features that protect against likely
hazards from rotating components, unless magniX can show, by test or
validated analysis, that the margin to rotor burst does not justify the
need for containment features. The intent of this special condition is
to prevent hazardous engine effects from structural failure of rotating
components and the rotating parts that are built into them.
Comment Summary: Textron stated that the wording in Special
Condition no. 30(a) relating to the required burst margin for the rotor
is vague. Textron suggested that the FAA incorporate the following
change to Special Condition no. 30(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 unconditionally rules out the
possibility of a rotor burst.''
FAA Response: The FAA agrees with the proposed change and has
modified Special Condition no. 30(a) to incorporate Textron's
suggestion.
Comment Summary: Airbus stated that experience with electrical
generators has shown that axial ejection of debris might induce severe
damage to surroundings. Airbus stated that an axial containment
demonstration is feasible for electric engines and generators, and
therefore should be required by the FAA. Airbus said that this special
condition should require magniX to show full containment capability,
eliminating the need to identify forward- and aft-ejected debris in the
engine installation manual. Airbus recommended that the FAA modify
Special Condition no. 30(a) to state, ``The design of the engine must
provide for axial and radial containment of the rotating components . .
.'' Airbus also recommended the FAA modify Special Condition no. 30(b)
to state, ``If the margin to burst shows the case must have containment
features in the event of failure, the case must provide axial and
radial containment of the failed rotating components.''
FAA Response: These special conditions apply only to the magniX
engine designs. Special Condition no. 30(b) is similar to Sec.
33.94(a), Blade containment and rotor unbalance tests, and Sec.
33.19(a), Durability, except this special condition includes the engine
rotors. This special condition allows magniX to approach containment
like turbine engines or provide full containment, as suggested in the
comment. If a magniX engine design cannot contain the rotors, life
limits will be applied in accordance with Special Condition no. 13
(Critical and life-limited parts). Therefore the FAA did not change
this special condition as a result of this comment.
Comment Summary: EASA stated that the intent of the proposed
Special Condition no. 30(b) is not clear, since that paragraph requests
the case to provide containment of the failed rotating component while
requesting that the applicant define the energy level, the trajectory,
and the size of the released fragments. EASA asked the FAA to rewrite
Special Condition no. 30(b) to be differentiated from Special Condition
no. 30(a). EASA commented that Special Condition no. 30(b) should be
dedicated to those cases where containment is not ensured.
FAA Response: Special Condition no. 30(b) provides a level of
protection similar to that provided by FAA regulations that manage
turbine engine blade failures, except it includes the engine rotors. It
precludes the release of high-energy debris radially outward of the
rotors. If the magniX engines qualify for the provisions in Special
Condition no. 30(b), fragments resulting from rotor damage, and that
travel forward or aft of the containment plane, must have their energy
levels and trajectories defined. The magniX engine configuration and
declared containment capabilities would determine if compliance with
Special Condition no. 30(b) is required. The FAA made no change to this
special condition as a result of this comment.
Special Condition No. 31, Operation With a Variable Pitch Propeller
The FAA proposed that Special Condition no. 31 would require magniX
to conduct functional demonstrations, including feathering, negative
torque, negative thrust, and reverse thrust operations, as applicable,
based on the propeller or fan's variable pitch functions that are
planned for use on these electric engines, with a representative
propeller. Also, since these electric engines may be installed with a
variable pitch propeller, the special condition associated with the
operation with a variable pitch propeller or fan is necessary.
Comment Summary: TCCA commented that, in addition to the propeller
control, there is a risk that an electric engine controller could fail
and result in reverse engine rotation. TCCA suggested that the FAA add
a special condition that considers and minimizes the potential for
engine controller failures that could result in reverse engine
rotation.
FAA Response: The FAA does not agree with the comment. Section
33.75(g)(2) provides a list of hazardous engine effects. The list
includes thrust in the opposite direction. Special Condition no.
17(d)(2) defines hazardous engine effects as those in Sec.
33.75(g)(2), with several additions specifically applicable to these
electric engines. These special conditions address the failure
described in the comment.
Comment Summary: TCCA recommended revising the Special Condition
no. 31 text to read, ``. . . with a representative propeller or fan.
These demonstrations may be conducted in a manner acceptable to the
Administrator as part . . .''.
FAA Response: The FAA has modified final Special Condition no. 31
to allow the Administrator to determine if a test is acceptable.
[[Page 53530]]
Special Condition No. 32, General Conduct of Tests
The FAA proposed that Special Condition no. 32 would require magniX
to (1) include scheduled maintenance in the engine ICA before
certification; (2) include any maintenance, in addition to the
scheduled maintenance, that was needed during the test to satisfy the
requirement; and (3) conduct additional tests that the Administrator
finds necessary, warranted by the test results.
The term ``excessive,'' as it is used in proposed Special Condition
nos. 32(b)(1) and (2), describes the frequency of unplanned engine
maintenance and the frequency of unplanned test stoppages that are
needed to address engine issues that prevent the engine from completing
the tests. Deciding if unplanned maintenance or test stoppages are
excessive requires an objective assessment of the reasons for the test
interruptions. For example, magniX may not be able to simulate a
realistic engine operating environment and may need to integrate test-
enabling equipment to achieve the test goals. The test facility
equipment may fail or cause an engine to fail during a test. Therefore,
unplanned maintenance might not affect the certification test results,
but if the FAA considers the maintenance or test stoppages to be
``excessive,'' additional testing or unforeseen ICA may be required to
comply with the certification requirements.
Comment Summary: Rolls-Royce stated that it supports the
clarifications in Special Condition no. 32(b) with the understanding
that the term ``excessive'' in Special Condition nos. 32(b)(1) and
32(b)(2) allows for the rectification of some failures while the test
continues. Rolls-Royce suggested that aircraft engines that operate
using aviation fuel, operating at the extreme physical conditions
required by the endurance tests, sometimes suffer a failure that is
unrelated to the test conditions. The ability to review the failure
with the FAA, rectify the failure, and continue the test is an
important aspect of conducting these tests.
FAA Response: The FAA's assessment of whether unplanned service and
maintenance during testing are ``excessive'' could include a variety of
factors, such as the causes of the stoppage, the effects of test
facility equipment, difficulties in simulating a realistic engine
operating environment, and whether the engine requires modifications to
complete the test. The applicant could also show that unplanned
maintenance did not affect the certification test results. The FAA did
not change this special condition as a result of this comment.
Comment Summary: TCCA commented that these special conditions do
not address the emerging issue of single event effects, which the FAA
is currently addressing via issue papers. TCCA recommended
incorporating those issue papers into the special condition.
FAA Response: The FAA does not agree with the comment. The issue
paper that TCCA referenced is applicable to engines that operate at
high altitudes and high latitudes. Special Condition nos. 10 and 17
require magniX to account for the intended aircraft application. If
magniX engines can operate at high altitudes and high latitudes, they
could apply the referenced issue paper to the certification program.
The FAA made no changes to these special conditions as a result of this
comment.
Comment Summary: TCCA recommended that the FAA clarify the
requirement in Special Condition no. 32(a) by including a reference to
14 CFR 33.4, Instructions for continued airworthiness.
FAA Response: The FAA has modified the special condition to add the
requested reference to Sec. 33.4 to clarify that magniX must provide
the service and maintenance instructions in accordance with the ICA.
Applicability
As discussed above, these special conditions are applicable to the
magniX magni350 and magni650 Model engines. Should magniX apply at a
later date for a change to the type certificate to include another
model on the same type certificate incorporating the same novel or
unusual design feature, these special conditions would apply to that
model as well.
Conclusion
This action affects only magniX magni350 and magni650 model
engines. It is not a rule of general applicability.
List of Subjects in 14 CFR Part 33
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
Authority Citation
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for magniX USA, Inc., (magniX), magni350
and magni650 model engines. The applicant must also comply with the
certification procedures set forth in title 14, Code of Federal
Regulations (14 CFR) part 21.
1. Applicability
Unless otherwise noted in these special conditions, the design must
comply with the airworthiness standards for aircraft engines set forth
in 14 CFR part 33, except those airworthiness standards specifically
and explicitly applicable only to reciprocating and turbine aircraft
engines.
2. Engine Ratings and Operating Limits
In addition to Sec. 33.7(a), the design must comply with the
following:
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 engine 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.
3. Materials
The engine design must comply with 14 CFR 33.15.
4. Fire Protection
The engine design must comply with 14 CFR 33.17.
In addition, high-voltage electrical wiring interconnect systems
must be protected against arc faults. Any non-protected electrical
wiring interconnects must be analyzed to show that arc faults do not
cause a hazardous engine effect.
5. 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
Instructions for Continued Airworthiness (ICA).
6. Engine Cooling
The engine design and construction must comply with Sec. 33.21. In
addition, if cooling is required to satisfy the safety
[[Page 53531]]
analysis as described in Special Condition no. 17, the cooling system
monitoring features and usage must be documented in the engine
installation manual.
7. Engine-Mounting Attachments and Structure
The engine-mounting attachments and related engine structures must
comply with 14 CFR 33.23.
8. Accessory Attachments
The engine must comply with 14 CFR 33.25.
9. 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 Special
Condition no. 17(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 certified 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.
10. Engine Control Systems
(a) Applicability.
The requirements of this special condition 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 Special
Condition no. 27.
(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;
(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; and
(4) Not have any likely failure or malfunction that lead to local
events in the intended aircraft application.
(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 assure 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 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 Special
Condition no. 17(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
Special Condition no. 17(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 for starting
and operating the engine, including transient and steady-state voltage
limits, and any other characteristics necessary for safe operation of
the engine.
11. Instrument Connection
The applicant must comply with 14 CFR 33.29(a), (e), and (g).
(a) In addition, as part of the system safety assessment of Special
Condition no. 10(g), 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 flight
crew 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 before detection; or
(3) The probability of failure of the cooling system is extremely
remote.
12. Stress Analysis
(a) A mechanical, thermal, and electromagnetic stress analysis must
show a sufficient design margin to prevent unacceptable operating
characteristics and hazardous engine effects.
(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.
13. 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,
[[Page 53532]]
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 Special Condition no.
17(d)(2) of these special conditions.
(2) Life-limited part means a rotor and major structural static
part, the failure of which can result in a hazardous engine effect due
to low-cycle fatigue (LCF) mechanism or any LCF driven mechanism
coupled with creep. A life limit is an operational limitation that
specifies the maximum allowable number of flight cycles that a part can
endure before the applicant must remove it from the engine.
(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:
(1) An engineering plan that establishes and maintains that the
combination of loads, material properties, environmental influences,
and operating conditions, including the effects of engine parts
influencing these parameters, are sufficiently well-known and
predictable by validated analysis, test, or service experience. The
engineering plan must ensure each critical part or life-limited part is
withdrawn from service at an approved life before hazardous engine
effects can occur. The engineering plan must establish activities to be
executed both pre- and post-certification. In addition to the
activities that must be completed prior to certification, including a
reporting system that flows, back to magniX, problematic issues that
develop in engines while they operate in-service, to be addressed by
the design process. magniX must perform appropriate damage-tolerance
assessments to address the potential for failure from material,
manufacturing, and service-induced anomalies within the approved life
of the part. The approved life must be published in the mandatory ICA.
(2) A manufacturing plan that identifies the specific manufacturing
definition (drawings, procedures, specifications, etc.) necessary for
the manufacturer to consistently produce critical or life-limited parts
with the design attributes required by the engineering plan.
(3) A service-management plan defines in-service processes for
maintenance and repair of critical or life-limited parts that maintain
attributes consistent with those required by the engineering plan.
These processes must be part of the mandatory ICA.
14. 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 (a) and (b).
15. 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 safe for aircraft operation; and
(c) From the minimum torque to the highest-rated torque without
detrimental engine or aircraft effects to ensure aircraft structural
integrity or aircraft aerodynamic characteristics are not exceeded.
16. 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 any hazardous engine effects, as
specified in Special Condition no. 17(d)(2).
17. Safety Analysis
(a) The applicant must comply with Sec. 33.75(a)(1) and (a)(2)
using the failure definitions in Special Condition no. 17(d).
(b) If the failure of such elements is likely to result in
hazardous engine effects, then the applicant may show compliance by
reliance on the prescribed integrity requirements such as Sec. 33.15,
Special Condition no. 9, Special Condition no. 13, 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) and (e) using the
failure definitions in Special Condition no. 17(d) of these special
conditions.
(d) Unless otherwise approved by the Administrator, the following
definitions apply to the engine effects when showing compliance with
this condition:
(1) A minor engine effect does not prohibit the engine from meeting
its certificated performance requirements and the intended functions in
a manner consistent with Sec. 33.28(b)(1)(i), Sec. 33.28(b)(1)(iii)
and Sec. 33.28 (b)(1)(iv), and the engine complies with the
operability requirements such as Special Condition no. 15 (Power
response), Special Condition no. 25 (Operation demonstration), and
Special Condition no. 31 (Operation with a variable pitch propeller),
as appropriate.
(2) The engine effects in Sec. 33.75(g)(2) are hazardous engine
effects with the addition of:
(i) Electrocution of the crew, passengers, operators, maintainers,
or others; and
(ii) Blockage of cooling systems that are required for the engine
to operate within temperature limits.
(3) Any other engine effect is a major engine effect.
(e) The intended aircraft application must be taken into account to
assure the analysis of the engine system safety is valid.
18. Ingestion
(a) Ingestion from likely sources (foreign objects, birds, ice,
hail) must not result in hazardous engine effects defined by Special
Condition no. 17(d)(2), or unacceptable power loss.
(b) Rain ingestion must not result in an abnormal operation such as
shutdown, power loss, erratic operation, or power oscillations
throughout the engine operating range.
(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 or hazardous engine effects following potential
ingestion, then the features, attachments, or systems must be
documented in the engine installation manual.
(d) Ingestion sources that are not evaluated must be declared in
the engine installation manual.
19. Liquid Systems
(a) Each liquid 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 liquid system used for lubrication or cooling of engine
components is not self-contained, the
[[Page 53533]]
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 gas or
liquid 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 Special Condition no. 19(c) 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.
20. 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 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 declared
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, or electromagnetic. This survey must be shown by test,
validated analysis, or a combination thereof.
21. 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 special condition, 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
Special Condition no. 29.
22. 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 Special Conditions
nos. 23 and 26.
23. Endurance Demonstration
The applicant must subject the engine to an endurance
demonstration, acceptable to the Administrator, to demonstrate the
engine's limit capabilities.
The endurance demonstration must include increases and decreases of
the engine's power settings, and dwellings at the power settings for
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.
24. 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 to the Administrator the margin at
each rated condition. The demonstration must be repeated for all
declared duty cycles and associated ratings, and operating
environments, that would impact temperature limits.
25. 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.
26. 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.
27. System and Component Tests
The applicant must show that systems and components will perform
their intended functions in all declared environmental and operating
conditions.
28. 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 Special
Condition no. 17(d)(2), will occur.
29. Teardown Inspection
The applicant must comply with either (a) or (b) as follows:
(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 within service limits and eligible for
continued operation in accordance with the information submitted for
showing compliance with Sec. 33.4, Instructions for Continued
Airworthiness.
(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 beginning of the endurance and durability demonstrations.
(b) Non-Teardown evaluation.
If a teardown is not performed for all engine components, then the
life limits for these components and lubricants must be established
based on the endurance and durability demonstrations and documented in
the ICA in accordance with Sec. 33.4.
30. Containment
The engine must provide containment features that 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 that the case must have
containment features in the event of failure, the case must provide for
the containment of the failed
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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.
31. 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.
32. 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 Sec. 33.4.
(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 special conditions, 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.
Issued in Kansas City, Missouri, on September 10, 2021.
Patrick R. Mullen,
Manager, Technical Innovation Policy Branch, Policy and Innovation
Division, Aircraft Certification Service.
[FR Doc. 2021-19926 Filed 9-24-21; 8:45 am]
BILLING CODE 4910-13-P