Document ID: FAA-2017-1128-0002
Agency: faa
Document Type: Rule
Title: Special Conditions: Bell Helicopter Textron, Inc. (BHTI), Model 525 Helicopters; Control Margin Awareness
Posted Date: 2018-10-12T04:00Z

[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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