[Federal Register Volume 89, Number 167 (Wednesday, August 28, 2024)]
[Proposed Rules]
[Pages 68833-68837]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-19329]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 27

[Docket No. FAA-2024-0875; Notice No. 27-24-01-SC]


Special Conditions: Skyryse, Robinson Helicopter Company Model 
R66 Helicopter; Interaction of Systems and Structures

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

-----------------------------------------------------------------------

SUMMARY: This action proposes special conditions for the Robinson 
Helicopter Company (Robinson) Model R66 helicopter. This helicopter, as 
modified by Skyryse, will have a novel or unusual design feature when 
compared to the state of technology envisioned in the airworthiness 
standards for normal category helicopters. This design feature is a 
novel control input and fly-by-wire (FBW) system. The applicable 
airworthiness regulations do not contain

[[Page 68834]]

adequate or appropriate safety standards for this design feature. These 
proposed 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: Send comments on or before October 15, 2024.

ADDRESSES: Send comments identified by Docket No. FAA-2024-0875 using 
any of the following methods:
    Federal eRegulations Portal: Go to www.regulations.gov and follow 
the online instructions for sending your comments electronically.
    Mail: Send comments to Docket Operations, M-30, U.S. Department of 
Transportation (DOT), 1200 New Jersey Avenue SE, Room W12-140, West 
Building Ground Floor, Washington, DC, 20590-0001.
    Hand Delivery or Courier: Take comments to Docket Operations in 
Room W12-140 of the West Building Ground Floor at 1200 New Jersey 
Avenue SE, Washington, DC, between 9 a.m. and 5 p.m., Monday through 
Friday, except Federal holidays.
    Fax: Fax comments to Docket Operations at 202-493-2251.
    Docket: Background documents or comments received may be read at 
www.regulations.gov at any time. Follow the online instructions for 
accessing the docket or go to Docket Operations in Room W12-140 of the 
West Building Ground Floor at 1200 New Jersey Avenue SE, Washington, 
DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays.

FOR FURTHER INFORMATION CONTACT: Daniel Moore, Airframe Section, AIR-
622, Technical Policy Branch, Policy and Standards Division, Aircraft 
Certification Service, Federal Aviation Administration, 901 Locust, 
Kansas City, MO 64106; telephone (303) 342-1066; email 
[email protected].

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested people to take part in this rulemaking 
by sending written comments, data, or views. The most helpful comments 
reference a specific portion of the proposed special conditions, 
explain the reason for any recommended change, and include supporting 
data.
    The FAA will consider all comments received by the closing date for 
comments, and will consider comments filed late if it is possible to do 
so without incurring delay. The FAA may change these special conditions 
based on the comments received.

Privacy

    Except for Confidential Business Information (CBI) as described in 
the following paragraph, and other information as described in title 
14, Code of Federal Regulations (14 CFR) 11.35, the FAA will post all 
comments received without change to www.regulations.gov, including any 
personal information you provide. The FAA will also post a report 
summarizing each substantive verbal contact received about these 
special conditions.

Confidential Business Information

    Confidential Business Information (CBI) is commercial or financial 
information that is both customarily and actually treated as private by 
its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), 
CBI is exempt from public disclosure. If your comments responsive to 
these special conditions contain commercial or financial information 
that is customarily treated as private, that you actually treat as 
private, and that is relevant or responsive to these special 
conditions, it is important that you clearly designate the submitted 
comments as CBI. Please mark each page of your submission containing 
CBI as ``PROPIN.'' The FAA will treat such marked submissions as 
confidential under the FOIA, and the indicated comments will not be 
placed in the public docket of these proposed special conditions. Send 
submissions containing CBI to the individual listed in the For Further 
Information Contact section above. Comments the FAA receives, which are 
not specifically designated as CBI, will be placed in the public docket 
for these proposed special conditions.

Background

    On April 10, 2023, Skyryse applied for a supplemental type 
certificate for removal of the mechanical control system and 
installation of a computer controlled flight control system in the 
Model R66 helicopter. The Robinson Model R66 helicopter, currently 
approved under Type Certificate No. R00015LA, is a single engine normal 
category rotorcraft. The maximum take-off weight is 2,700 pounds, with 
a maximum seating capacity of five passengers.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Skyryse must show that the 
Robinson Model R66 helicopter, as changed, continues to meet the 
applicable provisions of the regulations listed in Type Certificate No. 
R00015LA or the applicable regulations in effect on the date of 
application for the change, except for earlier amendments as agreed 
upon by the FAA.
    If the Administrator finds that the applicable airworthiness 
regulations do not contain adequate or appropriate safety standards for 
the Robinson Model R66 helicopter because of a novel or unusual design 
feature, special conditions are prescribed under the provisions of 
Sec.  21.16.
    Special conditions are initially applicable to the model for which 
they are issued. Should the applicant apply for a supplemental type 
certificate to modify any other model included on the same type 
certificate to incorporate the same novel or unusual design feature, 
these special conditions would also apply to the other model under 
Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Robinson Model R66 helicopter must comply with the 
fuel-vent and exhaust-emission requirements of 14 CFR part 34, and the 
noise-certification requirements of 14 CFR part 36.
    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.  21.101.

Novel or Unusual Design Feature

    The Robinson Model R66 helicopter will incorporate the following 
novel or unusual design feature:
    Novel control input and FBW system.

Discussion

    Skyryse is proposing to install an FBW flight control system (FCS) 
intended to replace the current hydraulicly boosted mechanical primary 
FCS, on a Robinson Model R66 helicopter. FBW systems are new to part 27 
rotorcraft and as such, the rotorcraft FCS will now contain control 
functions that affect the static strength of rotorcraft structure.
    These proposed special conditions would give the applicant an 
option to offset the structural factor of safety based on the 
probability of system failure. These proposed special conditions apply 
to systems that can induce loads on the airframe or change the response 
of the rotorcraft to maneuvers or to control inputs, as a result of 
failure. Some potential examples include part 27 rotorcraft equipped 
with FBW or fly-by-light FCSs, autopilots, stability augmentation 
systems, load alleviation systems, flutter control systems, fuel 
management systems, and other systems that either directly or as a 
result of failure or

[[Page 68835]]

malfunction affect structural performance.
    The FAA has issued special conditions for the interaction of 
systems and structures to other aircraft in the past (parts 23, 25, and 
29). Active flight control systems are capable of providing automatic 
responses to inputs from sources other than the pilots. These automatic 
systems may become inoperative or may operate in a degraded mode, which 
could impact the loads envelope and rotorcraft static strength.
    Therefore, it is necessary to determine the structural factors of 
safety and operating margins such that the joint probability of 
structural failures due to application of loads during system 
malfunctions is not greater than that found in rotorcraft equipped with 
earlier technology control systems. To achieve this objective, it is 
necessary to define the failure conditions with their associated 
frequency of occurrence in order to determine the structural factors of 
safety and operating margins that will ensure an acceptable level of 
safety.
    The proposed 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.

Applicability

    As discussed above, these proposed special conditions are 
applicable to the model for which they are issued. Should the applicant 
apply for a supplemental type certificate to modify any other model 
included on the same type certificate to incorporate the same novel or 
unusual design feature, these special conditions would apply to the 
other model as well.

Conclusion

    This action affects only a certain novel or unusual design feature 
on one model of helicopter. It is not a rule of general applicability 
and affects only the applicant who applied to the FAA for approval of 
these features on the helicopter.

List of Subjects in 14 CFR Part 27

    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, and 
44704.

The Proposed Special Conditions

    Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions as part of the type certification basis 
for Robinson Model R66 helicopters, as modified by Skyryse.

Interaction of Systems and Structures

    For rotorcraft equipped with systems that affect structural 
performance, either directly or as a result of a failure or 
malfunction, the influence of these systems and their failure 
conditions must be taken into account when showing compliance with the 
requirements of subparts C and D of part 27 of title 14 of the Code of 
Federal Regulations (14 CFR).
    The following criteria must be used for showing compliance with 
these special conditions:
    (a) The criteria defined herein only address the direct structural 
consequences of the system responses and performance. They cannot be 
considered in isolation but should be included in the overall safety 
evaluation of the rotorcraft. These criteria may, in some instances, 
duplicate standards already established for this evaluation. These 
criteria are only applicable to structures whose failure could prevent 
continued safe flight and landing. Specific criteria that define 
acceptable limits on handling characteristics or stability 
requirements, when operating in the system degraded or inoperative 
mode, are not provided in these special conditions.
    (b) Depending upon the specific characteristics of the rotorcraft, 
additional studies may be required that go beyond the criteria provided 
in these special conditions in order to demonstrate the capability of 
the rotorcraft to meet other realistic conditions such as alternative 
gust or maneuver descriptions for a rotorcraft equipped with a load 
alleviation system.
    (c) The following definitions are applicable to these special 
conditions.
    (1) Structural performance: Capability of the rotorcraft to meet 
the structural requirements of 14 CFR part 27.
    (2) Flight limitations: Limitations that can be applied to the 
rotorcraft flight conditions following an in-flight occurrence and that 
are included in the flight manual (e.g., speed limitations, avoidance 
of severe weather conditions, etc.).
    (3) Operational limitations: Limitations, including flight 
limitations that can be applied to the rotorcraft operating conditions 
before dispatch (e.g., fuel, payload, and master minimum equipment list 
limitations).
    (4) Failure condition: The term failure condition is the same as 
that used in Sec.  27.1309; however, these special conditions apply 
only to system failure conditions that affect the structural 
performance of the rotorcraft (e.g., system failure conditions that 
induce loads, change the response of the rotorcraft to inputs such as 
gusts or pilot actions, or lower flutter margins).

Effects of Systems on Structures

    (a) General. The following criteria will be used in determining the 
influence of a system and its failure conditions on the rotorcraft 
structure.
    (b) System fully operative. With the system fully operative, the 
following apply:
    (1) Limit loads must be derived in all normal operating 
configurations of the system from all the limit conditions specified in 
subpart C (or used in lieu of those specified in subpart C), taking 
into account any special behavior of such a system or associated 
functions or any effect on the structural performance of the rotorcraft 
that may occur up to the limit loads. In particular, any significant 
nonlinearity (rate of displacement of control surface, thresholds, or 
any other system nonlinearities) must be accounted for in a realistic 
or conservative way when deriving limit loads from limit conditions.
    (2) The rotorcraft must meet the strength requirements of part 27 
(static strength, residual strength), using the specified factors to 
derive ultimate loads from the limit loads defined above. The effect of 
nonlinearities must be investigated beyond limit conditions to ensure 
the behavior of the system presents no anomaly compared to the behavior 
below limit conditions. However, conditions beyond limit conditions 
need not be considered when it can be shown that the rotorcraft has 
design features that will not allow it to exceed those limit 
conditions.
    (3) The rotorcraft must meet the flutter requirements of Sec.  
27.629.
    (c) System in the failure condition. For any system failure 
condition not shown to be extremely improbable, the following apply:
    (1) At the time of occurrence. Starting from 1-g level flight 
conditions, a realistic scenario, including pilot corrective actions, 
must be established to determine the loads occurring at the time of 
failure and immediately after the failure.
    (i) For static strength substantiation, these loads multiplied by 
an appropriate factor of safety that is related to the probability of 
occurrence of the failure, are ultimate loads to be considered for 
design. The factor of safety is defined in Figure 1.

[[Page 68836]]

[GRAPHIC] [TIFF OMITTED] TP28AU24.498

    (ii) For residual strength substantiation, the rotorcraft must be 
able to withstand two thirds of the ultimate loads defined in paragraph 
(c)(1)(i) of these special conditions.
    (iii) Freedom from flutter and divergence must be shown under any 
condition of operation including:
    (A) Airspeeds up to 1.11 VNE (power on and power off).
    (B) Main rotor speeds from 0.95 x the minimum permitted speed up to 
1.05 x the maximum permitted speed (power on and power off).
    (C) The critical combinations of weight, center of gravity 
position, load factor, altitude, speed, and power condition.
    (iv) For failure conditions that result in excursions beyond 
operating limitations, freedom from flutter and divergence must be 
shown to increased speeds, so that the margins intended by paragraph 
(c)(1)(iii) of these special conditions are maintained.
    (v) Failures of the system that result in forced structural 
vibrations (oscillatory failures) must not produce loads that could 
result in detrimental deformation of primary structure.
    (2) For the continuation of the flight. For the rotorcraft in the 
system failed state, and considering any appropriate reconfiguration 
and flight limitations, the following apply:
    (i) The loads derived from the following conditions (or used in 
lieu of the following conditions) at speeds up to VNE (power 
on and power off) (or the speed limitation prescribed for the remainder 
of the flight) and at the minimum and maximum main rotor speeds (if 
applicable) must be determined:
    (A) the limit symmetrical maneuvering conditions specified in 
Sec. Sec.  27.337 and Sec.  27.339;
    (B) the limit gust conditions specified in Sec.  27.341;
    (C) the limit yaw maneuvering conditions specified in Sec.  27.351;
    (D) the limit unsymmetrical conditions specified in Sec.  27.427; 
and
    (E) the limit ground loading conditions specified in Sec.  27.473.
    (ii) For static strength substantiation, each part of the structure 
must be able to withstand the loads in paragraph (c)(2)(i) of these 
special conditions multiplied by a factor of safety depending on the 
probability of being in this failure state. The factor of safety is 
defined in Figure 2.
[GRAPHIC] [TIFF OMITTED] TP28AU24.499


[[Page 68837]]


Qj = (Tj)(Pj)

Where:

Qj = Probability of being in failure condition j
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per hour)


    Note: If Pj is greater than 10-3 per flight hour, 
then a 1.5 factor of safety must be applied to all limit load 
conditions specified in subpart C.

    (iii) For residual strength substantiation, the rotorcraft must be 
able to withstand two thirds of the ultimate loads defined in paragraph 
(c)(2)(ii) of these special conditions.
    (iv) If the loads induced by the failure condition have a 
significant effect on fatigue or damage tolerance, then their effects 
must be taken into account.
    (v) Freedom from flutter and divergence must also be shown up to 
1.11 VNE (power on and power off), including any probable 
system failure condition combined with any damage required or selected 
for investigation by either Sec.  27.571(e) or Sec.  27.573(d).
    (3) Consideration of certain failure conditions may be required by 
other sections of 14 CFR part 27 regardless of calculated system 
reliability. Where analysis shows the probability of these failure 
conditions to be extremely improbable, criteria other than those 
specified in this paragraph may be used for structural substantiation 
to show continued safe flight and landing.
    (d) Failure indications. For system failure detection and 
indication, the following apply:
    (1) The system must be checked for failure conditions, not shown to 
be extremely improbable, that degrade the structural capability below 
the level required by part 27 or that significantly reduce the 
reliability of the remaining operational portion of the system. As far 
as reasonably practicable, the flight crew must be made aware of these 
failures before flight. Certain elements of the control system, such as 
mechanical and hydraulic components, may use special periodic 
inspections, and electronic components may use daily checks, in lieu of 
detection and indication systems to achieve the objective of this 
requirement. These other means of detecting failures before flight are 
considered certification maintenance requirements and must be limited 
to components that are not readily detectable by normal detection and 
indication systems, and where service history shows that inspections 
will provide an adequate level of safety.
    (2) The existence of any failure condition, not shown to be 
extremely improbable, during flight that could significantly affect the 
structural capability of the rotorcraft and for which the associated 
reduction in airworthiness can be minimized by suitable flight 
limitations, must be signaled to the flight crew. For example, failure 
conditions that result in a factor of safety between the rotorcraft 
strength and the loads of subpart C below 1.25, or flutter and 
divergence margins below 1.11 VNE (power on and power off), 
must be signaled to the crew during flight.
    (e) Dispatch with known failure conditions. If the rotorcraft is to 
be dispatched in a known system failure condition that affects 
structural performance, or that affects the reliability of the 
remaining operational portion of the system to maintain structural 
performance, then the provisions of these special conditions must be 
met, including the provisions of paragraph (b) for the dispatched 
condition and paragraph (c) for subsequent failures. Expected 
operational limitations may be taken into account in establishing Pj as 
the probability of failure occurrence for determining the safety margin 
in Figure 1. Flight limitations and expected operational limitations 
may be taken into account in establishing Qj as the combined 
probability of being in the dispatched failure condition and the 
subsequent failure condition for the safety margins in Figure 2. These 
limitations must be such that the probability of being in this combined 
failure state and then subsequently encountering limit load conditions 
is extremely improbable. No reduction in these safety margins is 
allowed if the subsequent system failure rate is greater than 
10-3 per flight hour.

    Issued in Kansas City, Missouri, on August 22, 2024.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2024-19329 Filed 8-27-24; 8:45 am]
BILLING CODE 4910-13-P