Rule2024-27713
Special Conditions: Skyryse, Robinson Helicopter Company Model R66 Helicopter; Interaction of Systems and Structures
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
December 13, 2024
Effective
December 13, 2024
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
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.
Full Text
<html>
<head>
<title>Federal Register, Volume 89 Issue 240 (Friday, December 13, 2024)</title>
</head>
<body><pre>
[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 [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[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
<a href="/cdn-cgi/l/email-protection#4400252a2d21286a016a092b2b3621042225256a232b32"><span class="__cf_email__" data-cfemail="8bcfeae5e2eee7a5cea5c6e4e4f9eecbedeaeaa5ece4fd">[email protected]</span></a>.
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 V<INF>NE</INF> (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 V<INF>NE</INF> (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<SUP>-3</SUP> 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 V<INF>NE</INF> (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 V<INF>NE</INF> (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<SUP>-3</SUP> 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
</pre><script data-cfasync="false" src="/cdn-cgi/scripts/5c5dd728/cloudflare-static/email-decode.min.js"></script></body>
</html>Indexed from Federal Register on December 13, 2024.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.