Document ID: FAA-2022-0349-0003
Agency: faa
Document Type: Rule
Title: Special Conditions: Airbus Model A321neo XLR Airplane; Flight-Envelope Protection Functions-General
Posted Date: 2023-02-27T05:00Z

[Federal Register Volume 88, Number 38 (Monday, February 27, 2023)]
[Rules and Regulations]
[Pages 12133-12134]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-03980]

 ========================================================================
 Rules and Regulations
                                                 Federal Register
 ________________________________________________________________________
 
 This section of the FEDERAL REGISTER contains regulatory documents 
 having general applicability and legal effect, most of which are keyed 
 to and codified in the Code of Federal Regulations, which is published 
 under 50 titles pursuant to 44 U.S.C. 1510.
 
 The Code of Federal Regulations is sold by the Superintendent of Documents. 
 
 ========================================================================
 

  Federal Register / Vol. 88, No. 38 / Monday, February 27, 2023 / 
Rules and Regulations  

[[Page 12133]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2022-0349; Special Conditions No. 25-820-SC]

Special Conditions: Airbus Model A321neo XLR Airplane; Flight-
Envelope Protection Functions--General

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Final special conditions.

-----------------------------------------------------------------------

SUMMARY: These special conditions are issued for the Airbus Model 
A321neo XLR airplanes. These airplanes will have a novel or unusual 
design feature when compared to the state of technology envisioned in 
the airworthiness standards for transport-category airplanes. This 
design feature is an electronic flight-control system that provides 
flight-envelope protections. 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: Effective March 29, 2023.

FOR FURTHER INFORMATION CONTACT: Troy Brown, Performance and 
Environment Section, AIR-625, Technical Innovation Policy Branch, 
Policy and Innovation Division, Aircraft Certification Service, Federal 
Aviation Administration, 1801 S Airport Rd., Wichita, KS 67209-2190; 
telephone and fax 405-666-1050; email [email protected].

SUPPLEMENTARY INFORMATION: 

Background

    On September 16, 2019, Airbus applied for an amendment to Type 
Certificate No. A28NM to include the new Model A321neo XLR airplane. 
These airplanes are twin-engine, transport-category airplanes with 
seating for 244 passengers and a maximum takeoff weight of 222,000 
pounds.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Airbus must show that the 
Model A321neo XLR airplanes meet the applicable provisions of the 
regulations listed in Type Certificate No. A28NM, or the applicable 
regulations in effect on the date of application for the change, except 
for earlier amendments as agreed upon by the FAA.
    If the Administrator finds that the applicable airworthiness 
regulations (e.g., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the Airbus Model A321neo XLR airplanes 
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, or should any other model already included on 
the same type certificate be modified to incorporate 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 Airbus Model A321neo XLR airplanes must comply with the 
fuel-vent and 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 Sec.  11.19, in 
accordance with Sec.  11.38, and they become part of the type 
certification basis under Sec.  21.101.

Novel or Unusual Design Features

    The Airbus Model A321neo XLR airplanes will incorporate the 
following novel or unusual design feature:
    An electronic flight-control system that provides flight envelope 
protections.

Discussion

    Many new transport-category airplanes use advanced electronic 
flight-control systems (EFCS), which incorporate flight-envelope 
protection (limiting) designed to prevent the pilot from inadvertently 
or intentionally exceeding any number of flight-envelope parameters. 
Depending on a particular EFCS design, these limiting features may or 
may not be active in all normal and alternate flight-control modes, and 
may or may not be capable of being overridden by the pilot.
    The FAA currently applies 14 CFR 25.143 to airplanes incorporating 
EFCS. The purpose of Sec.  25.143 is to verify that operational 
maneuvers conducted within the operational envelope can be accomplished 
smoothly with average piloting skill, and without encountering a stall 
warning or other characteristics that might interfere with normal 
maneuvering, or without exceeding structural limits. The airplane 
response to control input should be predictable to the pilot. However, 
Sec.  25.143 does not adequately ensure that airplanes incorporating 
EFCS with flight-envelope protections will have a level of safety 
equivalent to that of existing standards.
    Envelope-protection functions are intended to reduce the likelihood 
of excursions, either commanded or uncommanded, to unintended or 
potentially hazardous airplane operating states. As a consequence of 
preventing excursions, these functions can also restrict aircraft 
maneuverability, and may introduce non-traditional behavior. The 
special conditions will ensure that flight-envelope protection 
functions support safe operation, and do not interfere with required 
maneuvering in normal and emergency operations, and in forseeable 
atmospheric conditions.
    The FAA previously issued separate special conditions for general 
limiting, normal load-factor limiting, high-speed limiting, and pitch 
and roll limiting for airplanes incorporating flight-envelope 
protection features. However, the FAA tasked the Aviation Rulemaking 
Advisory Committee (ARAC) in April 2014 (79 FR 20295) to develop 
recommended standards for fly-by-wire flight controls for general 
flight-envelope protection (limiting) similar to those provided for 
conventional control functions in 14 CFR 25.143. The ARAC 
recommended,\2\ among other things,

[[Page 12134]]

performance-based requirements that would encompass general limiting, 
normal load-factor limiting, high-speed limiting, and pitch and roll 
limiting which the FAA previously issued as separate special 
conditions. These proposed special conditions are based on that ARAC 
recommendation.
---------------------------------------------------------------------------

    \2\ FAA Aviation Rulemaking Advisory Committee, FTHWG Topic 1 
Envelope Protection, Recommendation Report--Rev. A, March, 2017, 
https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/09%20-%20FTHWG_Final_Report_Phase_2_RevA__Apr_2017.pdf.
---------------------------------------------------------------------------

    These special conditions provide the same level of safety as the 
prescriptive, design-specific special conditions the FAA has issued in 
the past for general limiting, normal load-factor limiting, high-speed 
limiting, and pitch and roll limiting, thus the FAA need not issue 
separate special conditions to address each of these areas.
    These special conditions are in addition to the requirements of 
Sec.  25.143.
    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.

Discussion of Comments

    The FAA issued notice of proposed Special Conditions No. 25-22-05-
SC for the Airbus Model A321neo XLR airplane, which was published in 
the Federal Register on November 17, 2022 (87 FR 68942).
    The FAA received one response from the Air Line Pilots Association 
supporting the special conditions. The special conditions are adopted 
as proposed.

Applicability

    As discussed above, these special conditions apply to Airbus Model 
A321neo XLR airplanes. Should Airbus apply later 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 series of airplanes. It is not a rule of general 
applicability.

List of Subjects in 14 CFR Part 25

    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, 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 Airbus Model A321neo XLR airplanes 
equipped with EFCS.
    In addition to Sec.  25.143, the following requirements apply:
    (a) Envelope protection functions must not unduly limit the 
maneuvering capability of the airplane, nor interfere with its ability 
to perform maneuvers required for normal and emergency operations.
    (b) Onset characteristics of each flight-envelope protection 
function must be appropriate to the phase of flight and type of 
maneuver, and must not conflict with the ability of the pilot to 
satisfactorily control the airplane flight path, speed, and attitude.
    (c) Excursions of a limited flight parameter beyond its nominal 
design-limit value due to dynamic maneuvering, airframe and system 
tolerances, and non-steady atmospheric conditions must not result in 
unsafe flight characteristics or conditions.
    (d) Operation of flight-envelope protection functions must not 
adversely affect aircraft control during expected levels of atmospheric 
disturbances, nor impede the application of recovery procedures in case 
of wind shear.
    (e) Simultaneous action of flight-envelope protection functions 
must not result in adverse coupling or adverse priority.
    (f) In case of abnormal attitude or excursion of flight parameters 
outside the protected boundaries, operation of flight-envelope 
protection functions must not hinder airplane recovery.

    Issued in Kansas City, Missouri, on February 22, 2023.
Patrick R. Mullen,
Manager, Technical Innovation Policy Branch, Policy and Innovation 
Division, Aircraft Certification Service.
[FR Doc. 2023-03980 Filed 2-24-23; 8:45 am]
BILLING CODE 4910-13-P