83 FR 51623 - Special Conditions: Bell Helicopter Textron, Inc. (BHTI), Model 525 Helicopters; Flight Envelope Protection

DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration

Federal Register Volume 83, Issue 198 (October 12, 2018)

These special conditions are issued for the BHTI Model 525 helicopter. This helicopter will have a novel or unusual design feature associated with fly-by-wire flight control system (FBW FCS) flight envelope protection. 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.

[Federal Register Volume 83, Number 198 (Friday, October 12, 2018)]
[Rules and Regulations]
[Pages 51623-51624]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2018-22267]



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Rules and Regulations
                                                Federal Register
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Federal Register / Vol. 83, No. 198 / Friday, October 12, 2018 / 
Rules and Regulations

[[Page 51623]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 29

[Docket No.FAA-2017-1127; Notice No. 29-044-SC]


Special Conditions: Bell Helicopter Textron, Inc. (BHTI), Model 
525 Helicopters; Flight Envelope Protection

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 fly-by-wire flight control system (FBW FCS) flight 
envelope protection. 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 FBW FCS will 
contain an advanced flight control system that will alter the nominal 
flight control laws to ensure that the aircraft remains in a 
predetermined flight envelope. These Flight Envelope Protection (FEP) 
features prevent the pilot or autopilot functions from making control 
commands that would force the aircraft to exceed its structural, 
aerodynamic, or operating limits. The design and construction 
standards, specifically 14 CFR Section 29.779(a), require that movement 
of the flight controls results in a corresponding sense of aircraft 
motion in the same axis. The airworthiness standards for an automatic 
pilot system in Section 29.1329 covers design requirements for basic 
operation of the system but does not address dynamic flight envelope 
limitations imposed by the automatic pilot system. Currently there are 
no specific airworthiness requirements that address FBW FCS FEP in 
rotorcraft. The special conditions will require the minimum safety 
standard for the FEP features.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, BHTI must show that the Model 
525 helicopter meets the applicable 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 Sec.  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 will incorporate the following novel 
or unusual design features: FBW FCS incorporating FEP features. FEP is 
used to prevent the pilot or an autopilot from making control commands 
that would force the rotorcraft to exceed its structural, aerodynamic, 
or operating limits. To accomplish this envelope limiting, the FCS 
control laws change as the limit is approached or exceeded.

Discussion

    These special conditions require the minimum safety standard for 
the flight envelope protection features. The FEP features must meet 
requirements for handling qualities, compatibility of flight parameter 
limit values, response to dynamic maneuvering, and failure modes.

Discussion of Comments

    Notice of proposed special conditions No. 29-044-SC for the BHTI 
Model 525 helicopter was published in the Federal Register on June 6, 
2018 (83 FR 26226). 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.

[[Page 51624]]

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:

Flight Envelope Protection

    The Flight Envelope Protection (FEP) features of the flight control 
system (FCS) must meet the following requirements:
    a. Onset characteristics of each envelope protection feature must 
be smooth, appropriate to the phase of flight and type of maneuver, and 
not in conflict with the ability of the pilot to satisfactorily change 
rotorcraft flight path, speed, or attitude within the approved flight 
envelope.
    b. Limit values of protected flight parameters (and if applicable, 
associated warning thresholds) must be compatible with:
    1. Rotorcraft structural limits;
    2. Safe and controllable maneuvering of the rotorcraft;
    3. Margins to critical conditions. Dynamic maneuvering, airframe 
and system tolerances (both manufacturing and in-service), and non-
steady atmospheric conditions--in any appropriate combination and phase 
of flight--must not result in a limited flight parameter beyond the 
nominal design limit value that would cause unsafe flight 
characteristics;
    4. Rotor rotational speed limits;
    5. Blade stall limits; and
    6. Engine and transmission torque limits.
    c. The aircraft must be responsive to pilot-commanded dynamic 
maneuvering within a suitable range of the parameter limits that define 
the approved flight envelope.
    d. The FEP system must not create unusual or adverse flight 
characteristics when atmospheric conditions or unintentional pilot 
action causes the approved flight envelope to be exceeded.
    e. When simultaneous envelope limiting is active, adverse coupling 
or adverse priority must not result.
    f. Following a single FEP failure shown to not be extremely 
improbable, the rotorcraft must:
    1. Be capable of continued safe flight and landing;
    2. Be capable of initial counteraction of malfunctions without 
requiring exceptional pilot skill or strength;
    3. Be controllable and maneuverable when operated with a degraded 
FCS, within a practical flight envelope identified in the Rotorcraft 
Flight Manual;
    4. Be capable of prolonged instrument flight without requiring 
exceptional pilot skill;
    5. Meet the controllability and maneuverability requirements of 14 
CFR part 29 Subpart B throughout a practical flight envelope; and
    6. Be safely controllable following any additional failure or 
malfunction shown to not be extremely improbable occurring within the 
approved flight envelope.

    Issued in Fort Worth, Texas, on October 3, 2018.
Jorge Castillo,
Acting Manager, Rotorcraft Standards Branch, Policy and Innovation 
Division, Aircraft Certification Services.
[FR Doc. 2018-22267 Filed 10-11-18; 8:45 am]
BILLING CODE 4910-13-P