Proposed Rule2024-11158
Special Conditions: Bell Textron Inc. (Bell) Model 525 Helicopter; Static Longitudinal Stability Compliance
Primary source
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Published
May 22, 2024
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
This action proposes special conditions for the Bell Model 525 helicopter. This helicopter will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport category helicopters. This design feature is a four-axis full authority digital fly-by-wire (FBW) flight control system (FCS) that provides for aircraft control through pilot input or coupled auto pilot 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 89 Issue 100 (Wednesday, May 22, 2024)</title>
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[Federal Register Volume 89, Number 100 (Wednesday, May 22, 2024)]
[Proposed Rules]
[Pages 44928-44930]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-11158]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 29
[Docket No. FAA-2024-0895; Notice No. 29-24-01-SC]
Special Conditions: Bell Textron Inc. (Bell) Model 525
Helicopter; Static Longitudinal Stability Compliance
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This action proposes special conditions for the Bell Model 525
helicopter. This helicopter will have a novel or unusual design feature
when compared to the state of technology envisioned in the
airworthiness standards for transport category helicopters. This design
feature is a four-axis full authority digital fly-by-wire (FBW) flight
control system (FCS) that provides for aircraft control through pilot
input or coupled auto pilot 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 July 8, 2024.
ADDRESSES: Send comments identified by Docket No. FAA-2024-0895 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.
[[Page 44929]]
Docket: Background documents or comments received may be read at
<a href="https://www.regulations.gov/">https://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: Gregory Thumann, Performance and
Environment Unit, AIR-621A, Technical Policy Branch, Policy and
Standards Division, Aircraft Certification Service, Federal Aviation
Administration, 1801 S Airport Road, Wichita, KS 67209; telephone and
fax (405) 666-1052; email <a href="/cdn-cgi/l/email-protection#b8ffcadddfd7cac196ff96ecd0cdd5d9d6d6f8ded9d996dfd7ce"><span class="__cf_email__" data-cfemail="b2f5c0d7d5ddc0cb9cf59ce6dac7dfd3dcdcf2d4d3d39cd5ddc4">[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
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 <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 December 15, 2011, Bell applied for a type certificate for a new
14 CFR part 29 transport category helicopter designated as the Model
525. Bell applied for multiple extensions to its certification
application, with the most recent occurring on September 21, 2023. The
helicopter is a medium twin-engine rotorcraft. The maximum takeoff
weight is 20,500 pounds, with a maximum capacity of 16 passengers and a
crew of 2.
Type Certification Basis
Under the provisions of 14 CFR 21.17, Bell must show that the Model
525 meets the applicable provisions of part 29, as amended by
Amendments 29-1 through 29-55 thereto. The Bell Model 525 certification
basis date is December 31, 2019.
If the Administrator finds that the applicable airworthiness
regulations (i.e., 14 CFR part 29) do not contain adequate or
appropriate safety standards for the Bell Model 525 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 type certificate for that model be amended
later to include any other model that incorporates 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 Bell Model 525 helicopter must comply with the 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. 21.17(a)(2).
Novel or Unusual Design Feature
The Bell Model 525 helicopter will incorporate the following novel
or unusual design feature: a four-axis full authority digital FBW FCS
that provides aircraft control through pilot input or coupled auto
pilot modes in addition to degraded modes.
Discussion
For a conventional rotorcraft having mechanical linkages from the
primary cockpit flight controls to the rotor, static longitudinal
stability means that a pull force on the controller (i.e., cyclic) will
result in a reduction in speed relative to the trim speed, and a push
force will result in a higher speed relative to the trim speed.
Longitudinal stability is required by the regulations 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 altitude, is provided to the pilot.
<bullet> Longitudinal stability provides gust stability.
The pitch control movement of the controller (i.e., 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. The relevant regulations in
part 29, which are Sec. Sec. 29.173(b), 29.175 for visual flight rules
(VFR) operations, and Appendix B to part 29 sections IV and VII--
Airworthiness Criteria for Helicopter Instrument Flight, are inadequate
for the Bell 525 because the longitudinal flight control laws for the
Bell 525 provide neutral and negative static stability, rather than
positive static stability, within the normal operational envelope. As
detailed in Sec. 29.173(b) and considered in Advisory Circular (AC)
29.173A, ``Static Longitudinal Stability'' (AC 29.173A), which is
contained in AC 29-2C, ``Certification of Transport Category
Rotorcraft'' (AC 29-2C), and the positive control force stability
requirements in Appendix B to part 29, sections IV and VII, the slope
of the control position (i.e., cyclic) versus
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airspeed curve must be positive (i.e., provide positive static
stability) throughout the full range of altitude for which
certification is requested and with the throttle and collective pitch
held constant.
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.
In lieu of meeting the requirements of Sec. Sec. 29.173(b), 29.175
for VFR operations and the airworthiness criteria for helicopter
instrument flight requirements of Appendix B to part 29, sections IV
and VII, the proposed special conditions would require the rotorcraft
to be shown to have suitable longitudinal stability and acceptable
rotorcraft handling qualities. The suitable static longitudinal
stability must be primarily based on a positive control movement, which
is described as ``control sense of motion'' in AC 29.173A contained in
AC 29-2C. Additionally, the static longitudinal stability and
rotorcraft handling qualities are determined through an assessment of
pilot workload, cues, and pilot compensation for specific test
procedures performed during the flight test evaluation.
The language ``must be primarily based on a positive control
movement'' reflects a pilot's perception of aircraft control where the
first concern is that the control movements are primarily positive in
control movement. Once that is established, the pilot must observe that
the second concern of ``rotorcraft handling qualities'' is not degraded
or mis-aligned where the anticipated flight behavior is not what the
pilot is witnessing. The proposed special conditions address the
concern that these highly computer-controlled control systems can cause
the pilot to become disconnected or out-of-sync with the aircraft's
control. Such a situation can lead to control input errors and
undesirable feedback that can in turn result in loss of control.
Applicability
As discussed above, these proposed special conditions are
applicable to the model for which they are issued. Should the type
certificate for that model be amended later to include any other model
that incorporates 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.
List of Subjects in 14 CFR Part 29
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
In lieu of meeting the requirements of Sec. Sec. 29.173(b), 29.175
for VFR operations and the airworthiness criteria for helicopter
instrument flight requirements of Appendix B to part 29, sections IV
and VII, the Federal Aviation Administration (FAA) proposes the
following special conditions as part of the type certification basis
for Bell Model 525 helicopters.
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 primarily based on a positive control
movement in addition to acceptable rotorcraft handling qualities, both
of which are determined by assessing pilot workload, cues, and pilot
compensation for specific test procedures during the flight test
evaluation.
Issued in Des Moines, Washington, on May 16, 2024.
Caspar K. Wang,
Manager, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service.
[FR Doc. 2024-11158 Filed 5-21-24; 8:45 am]
BILLING CODE 4910-13-P
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