Proposed Rule2025-20611
Special Conditions: Skyryse, Robinson Model R66 Helicopter; Static Longitudinal Stability
Primary source
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Published
November 21, 2025
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
This action proposes special conditions for a modified 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 rotorcraft. This design features a four-axis full authority digital fly-by-wire (FBW) flight control system (FCS), which provides aircraft control through pilot input or coupled autopilot modes. The applicable airworthiness regulations do not contain 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.
Full Text
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<title>Federal Register, Volume 90 Issue 223 (Friday, November 21, 2025)</title>
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[Federal Register Volume 90, Number 223 (Friday, November 21, 2025)]
[Proposed Rules]
[Pages 52569-52570]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-20611]
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Proposed Rules
Federal Register
________________________________________________________________________
This section of the FEDERAL REGISTER contains notices to the public of
the proposed issuance of rules and regulations. The purpose of these
notices is to give interested persons an opportunity to participate in
the rule making prior to the adoption of the final rules.
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Federal Register / Vol. 90, No. 223 / Friday, November 21, 2025 /
Proposed Rules
[[Page 52569]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 27
[Docket No. FAA-2025-2303; Notice No. 27-25-01-SC]
Special Conditions: Skyryse, Robinson Model R66 Helicopter;
Static Longitudinal Stability
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This action proposes special conditions for a modified
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 rotorcraft. This design features a four-axis full authority
digital fly-by-wire (FBW) flight control system (FCS), which provides
aircraft control through pilot input or coupled autopilot modes. The
applicable airworthiness regulations do not contain 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 January 5, 2026.
ADDRESSES: Send comments identified by Docket No. FAA-2025-2303 using
any of the following methods:
Federal eRegulations Portal: Go to <a href="http://www.regulations.gov">www.regulations.gov</a> 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
<a href="http://www.regulations.gov">www.regulations.gov</a> 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: Mitch Soth, Product Policy Management,
AIR-62B, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service, Federal Aviation Administration, FAA
Southwest Regional Office, 10101 Hillwood Parkway, Fort Worth, TX
76177; telephone 817-222-5104; email <a href="/cdn-cgi/l/email-protection#f79a9e83949fd98498839fb7919696d9909881"><span class="__cf_email__" data-cfemail="3a57534e59521449554e527a5c5b5b145d554c">[email protected]</span></a>.
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
refer to 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 <a href="http://www.regulations.gov">www.regulations.gov</a>, 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 (STC) for the installation of novel control inputs and a
fly-by-wire system in the Model R66 helicopter. The Robinson Model R66
helicopter, currently approved under Type Certificate No. R00015LA, is
a single-engine, five passenger helicopter with a maximum takeoff
weight of 2,700 pounds.
Type Certification Basis
Under the provisions of 14 CFR 21.101, Skyryse must show that the
changes to the Robinson Model R66 helicopter continue to comply with
the applicable provisions of the regulations specified in Type
Certificate No. R00015LA or with the regulations in effect on the date
of the application for the change, except for any earlier amendments as
agreed upon by the FAA.
If the Administrator finds that the applicable airworthiness
regulations (e.g., 14 CFR part 27) 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
[[Page 52570]]
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 title 14, Code of Federal Regulations (14 CFR) Sec.
11.38, and they become part of the type certification basis under Sec.
21.101.
Novel or Unusual Design Features
The Robinson Model R66 helicopter will incorporate the following
novel or unusual design feature:
A four-axis full authority digital FBW FCS that provides aircraft
control through pilot control inputs or coupled autopilot modes in
addition to degraded modes.
Discussion
The Skyryse Robinson Model R66 helicopter is configured with a FBW
FCS, which needs to be evaluated for acceptable static stability
characteristics.
For conventional rotorcraft having mechanical linkages from the
primary cockpit flight controls to the rotor, static longitudinal
stability means that a pull displacement or force on the cyclic will
result in a reduction of speed relative to the trim speed, and that a
push displacement or force will result in a higher speed relative to
the trim speed. Acceptable longitudinal stability is necessary for the
following reasons:
<bullet> Airspeed change cues are provided to the pilot through
increased and decreased forces on the controller.
<bullet> Short periods of unattended control of the rotorcraft do
not result in significant changes in attitude, airspeed, or load
factor.
<bullet> A predictable pitch response is provided to the pilot.
<bullet> An acceptable level of pilot workload, to attain and
maintain trim speed and attitude, is provided to the pilot.
<bullet> Longitudinal stability provides gust stability.
The pitch control movement of the cyclic for the FBW FCS is an
attitude command, which results in a rotor movement to attain the
commanded pitch attitude. The flight path commanded by the initial
cyclic input will remain stick-free until the pilot gives another
command. This control function is applied during ``normal'' control
laws within the approved flight envelope.
Sections 27.171, 27.173, and 27.175 establish the minimum
requirements for static longitudinal stability for visual flight rules
(VFR), and appendix B of part 27, sections IV and VII, ``Airworthiness
Criteria for Helicopter Instrument Flight'', provides the airworthiness
criteria for helicopter instrument flight. However, these requirements
are inadequate for the modified Skyryse Robinson R-66 helicopter
because the longitudinal control laws may permit neutral or negative
static stability, rather than requiring positive static stability
throughout the approved flight envelope. As detailed in Sec. 27.173(b)
and considered in Advisory Circular (AC) 27.173(A), ``Static
Longitudinal Stability'', which is contained within AC 27-1B,
``Certification of Normal Category Rotorcraft'', and the positive
control force stability requirements in appendix B to part 27, sections
IV and VII, the slope of the control position (cyclic) versus the
airspeed curve must be positive (i.e., provide positive static
stability) throughout the full range of altitude for which
certification is requested with the throttle and collective pitch held
constant.
The design of the Skyryse FBW FCS is such that the static stability
requirements identified under part 27 and appendix B, section IV, may
not be met for all flight conditions.
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 the Model R66 of helicopters. 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), 40113, 44701, 44702, and 44704.
The Proposed Special Conditions
Accordingly, the FAA proposes the following special conditions as
part of the type certification basis for Robinson Model R66
helicopters, as modified by Skyryse.
In lieu of the requirements of Sec. Sec. 27.173(b) and 27.175 for
VFR operations, and the airworthiness criteria for helicopter
instrument flight requirements in part 27, appendix B, sections IV and
VII, the following special conditions apply:
The rotorcraft must be shown to have suitable longitudinal
stability in any condition normally encountered in service, including
the effects of atmospheric disturbance. The showing of suitable static
longitudinal stability must be based primarily on a positive control
movement (positive control sense of motion as referenced in AC
27.173A), in addition to rotorcraft handling qualities by assessing
pilot workload, cues, and pilot compensation for specific test
procedures during the flight test evaluation.
Issued in Kansas City, Missouri, on November 14, 2025.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service.
[FR Doc. 2025-20611 Filed 11-20-25; 8:45 am]
BILLING CODE 4910-13-P
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