[Federal Register Volume 83, Number 198 (Friday, October 12, 2018)]
[Rules and Regulations]
[Pages 51624-51625]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-22265]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 29
[Docket No.FAA-2017-1128; Notice No. 29-045-SC]
Special Conditions: Bell Helicopter Textron, Inc. (BHTI), Model
525 Helicopters; Control Margin Awareness
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the BHTI Model 525
helicopter. This helicopter will have a novel or unusual design feature
associated with the fly-by-wire flight control system (FBW FCS) in the
area of pilot awareness of the control margins remaining while
maneuvering the helicopter. 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: These special conditions are effective November 13, 2018.
FOR FURTHER INFORMATION CONTACT: George Harrum, Aerospace Engineer,
FAA, Rotorcraft Standards Branch, Policy and Innovation Division, 10101
Hillwood Pkwy., Fort Worth, TX 76177; telephone (817) 222-4087; email
[email protected].
SUPPLEMENTARY INFORMATION:
Background
On December 15, 2011, BHTI applied for a type certificate for a new
transport category helicopter designated as the Model 525. The Model
525 is a medium twin-engine rotorcraft. The design maximum takeoff
weight is 20,500 pounds, with a maximum capacity of 19 passengers and a
crew of 2.
The BHTI Model 525 helicopter will be equipped with a four-axis
full authority digital FBW FCS that provides for aircraft control
through pilot input and coupled flight director modes. The current 14
CFR part 29 regulations do not contain adequate standards for FBW FCS
with respect to control margin awareness. The airworthiness standards
for controllability and maneuverability of the rotorcraft are contained
in Sec. 29.143. These controllability requirements are compatible with
most FBW systems, while most of the maneuverability requirements are
not affected by FBW systems, except for the control margins. One of the
purposes of the rule is to ensure that control margins (at the rotor
and the anti-torque system level) are sufficient in the defined flight
envelope to avoid loss of control (that is, the rotorcraft has adequate
control power for the pilot to exit potentially hazardous flight
conditions). Implicit in this purpose is that the pilot is provided
with sufficient awareness of proximity to control limits. Because Sec.
29.143 was written to address hydro-mechanical flight control systems,
through which pilot awareness of control margins is provided by cyclic
and pedal position relative to cockpit control stops, the rule is
inadequate for certification of a FBW FCS, where there is no mechanical
link between the inceptor and the receptor. Without a constant
correlation between cockpit control and main or tail rotor actuator
positions, the FCS may not provide tactile control margin feedback to
the pilot through cockpit control position relative to the control
position physical stop or limit, for all flight conditions. The special
conditions will require the minimum safety standard to ensure awareness
of proximity to control limits at the main rotor and tail rotor is
provided to pilots of the Bell Model 525 helicopter.
Type Certification Basis
Under the provisions of 14 CFR 21.17, BHTI must show that the Model
525 helicopter meets the applicable
[[Page 51625]]
provisions of part 29, as amended by Amendment 29-1 through 29-55
thereto. The BHTI Model 525 certification basis date is December 31,
2013, the effective date of application to the FAA.
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 BHTI 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 or similar
novel or unusual design feature, the special conditions would also
apply to the other model under Sec. 21.101.
In addition to the applicable airworthiness regulations and special
conditions, the BHTI Model 525 helicopter must comply with the noise
certification requirements of 14 CFR part 36, and the FAA must issue a
finding of regulatory adequacy under section 611 of Public Law 92-574,
the ``Noise Control Act of 1972.''
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 Features
The BHTI Model 525 helicopter incorporates the following novel or
unusual design features: A four-axis full authority digital FBW FCS.
Pilot control inputs, through the mechanically linked cockpit controls
(cyclic, collective, directional pedals), are transmitted electrically
to each of the three Flight Control Computers (FCCs). The pilot control
input signals are then processed and transmitted to the hydraulic
flight control actuators which affect control of the main and tail
rotors.
Discussion
These special conditions require the minimum safety standard to
ensure awareness of proximity to control limits at the main rotor and
tail rotor is provided to pilots of the Bell Model 525 helicopter. The
system design must provide the pilot with sufficient awareness of
proximity to control limits, traditionally achieved through
conventional flight controls by the pilot's inherent awareness of
cyclic stick and pedal position relative to control stops.
Discussion of Comments
Notice of proposed special conditions No. 29-045-SC for the BHTI
Model 525 helicopter was published in the Federal Register on June 6,
2018 (83 FR 26225). No comments were received, and the special
conditions are adopted as proposed.
Applicability
As discussed above, these special conditions are applicable to the
BHTI Model 525 helicopter. Should BHTI apply at a later date for a
change to the type certificate to include another model incorporating
the same novel or unusual design feature, the special conditions would
apply to that model as well.
Conclusion
This action affects only certain novel or unusual design features
on one model of rotorcraft. It is not a rule of general applicability.
List of Subjects in 14 CFR Part 29
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 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 Bell Helicopter Textron, Inc., Model
525 helicopters:
Control Margin Awareness
In addition to the existing Sec. 29.143 requirements, the
following special condition applies: The system design must ensure that
the flight crew is made suitably aware whenever the means of primary
flight control approaches the limits of control authority. For the
context of this special condition, the term ``suitable'' indicates an
appropriate balance between nuisance and necessary operation.
Issued in Ft Worth, Texas, on October 3, 2018.
Jorge Castillo,
Acting Manager, Rotorcraft Standards Branch, Policy and Innovation
Division, Aircraft Certification Service.
[FR Doc. 2018-22265 Filed 10-11-18; 8:45 am]
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