83 FR 26226 - Special Conditions: Bell Helicopter Textron, Inc. (BHTI), Model 525 Helicopters; Flight Envelope Protection

DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration

Federal Register Volume 83, Issue 109 (June 6, 2018)

This action proposes special conditions 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 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.

[Federal Register Volume 83, Number 109 (Wednesday, June 6, 2018)]
[Proposed Rules]
[Pages 26226-26228]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2018-12077]


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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: Notice of proposed special conditions.

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SUMMARY: This action proposes special conditions 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 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 your comments on or before July 23, 2018.

ADDRESSES: Send comments identified by docket number [FAA-2017-1127] 
using any of the following methods:
     Federal eRegulations Portal: Go to http://www.regulations.gov 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 of 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 8 a.m., and 5 p.m., 
Monday through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://www.regulations.gov, including any personal 
information the commenter provides. Using the search function of the 
docket website, anyone can find and read the electronic form of all 
comments received into any FAA docket, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov at any time. Follow the online instructions 
for accessing the docket or go to the 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: George Harrum, Aerospace Engineer,

[[Page 26227]]

FAA, Rotorcraft Standards Branch, Policy and Innovation Division, 10101 
Hillwood Pkwy, Fort Worth, TX 76177; telephone (817) 222-4087; email 
[email protected].

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite 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 special conditions, explain the 
reason for any recommended change, and include supporting data.
    We will consider all comments we receive on or before the closing 
date for comments. We will consider comments filed late if it is 
possible to do so without incurring expense or delay. We may change 
these special conditions based on the comments we receive.

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 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 Sec.  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 
proposed 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 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 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

    The proposed special conditions will 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.

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 Proposed Special Conditions

    Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions 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 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

[[Page 26228]]

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 May 24, 2018.
Jorge Castillo,
Acting Manager, Rotorcraft Standards Branch, Policy and Innovation 
Division, Aircraft Certification Services.
[FR Doc. 2018-12077 Filed 6-5-18; 8:45 am]
BILLING CODE 4910-13-P