```

[Federal Register Volume 89, Number 240 (Friday, December 13, 2024)]
[Rules and Regulations]
[Pages 100730-100734]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-27713]

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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 27

[Docket No. FAA-2024-0875; Special Conditions No. 27-058-SC]

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

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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

SUMMARY: These special conditions are issued 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 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 December 13, 2024.

FOR FURTHER INFORMATION CONTACT: Daniel Moore, Airframe Section, AIR-
622, Technical Policy Branch, Policy and Standards Division, Aircraft

[[Page 100731]]

Certification Service, Federal Aviation Administration, 901 Locust, 
Kansas City, MO 64106; telephone (303) 342-1066; email 
[email protected].

SUPPLEMENTARY INFORMATION:

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 has proposed 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 special conditions would give the applicant an option to 
offset the structural factor of safety based on the probability of 
system failure. These 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 
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 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.

Discussion of Comments

    The FAA issued Notice of Proposed Special Conditions No. 27-24-01-
SC for the Robinson Model R66 helicopter, as modified by Skyryse, which 
was published in the Federal Register on August 28, 2024 (89 FR 68833).
    No comments were received, and the special conditions are adopted 
as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Robinson R66 helicopter. Should Skyryse apply at a later date for a 
supplemental type certificate to modify any other model included on 
Type Certificate No. R00015LA to incorporate the same novel or unusual 
design feature, these special conditions would apply to that model as 
well.
    Under standard practice, the effective date of final special 
conditions would be 30 days after the date of publication in the 
Federal Register. However, as the certification date for the Robinson 
R66 helicopter, as modified by Skyryse, is imminent, the FAA finds that 
good cause exists to make these special conditions effective upon 
publication.

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, 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 the Robinson R66 helicopter, 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

[[Page 100732]]

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 of this part (or used in lieu of those specified in subpart C 
of this part), 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.
[GRAPHIC] [TIFF OMITTED] TR13DE24.078

    (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.

[[Page 100733]]

    (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 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] TR13DE24.079

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 of this part, below 1.25, or 
flutter and divergence margins below 1.11 VNE (power on and

[[Page 100734]]

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) of these special 
conditions for the dispatched condition and paragraph (c) of these 
special conditions 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 November 21, 2024.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2024-27713 Filed 12-12-24; 8:45 am]
BILLING CODE 4910-13-P
```