Special Conditions: Airbus Model A321neo XLR Airplanes; Flight Envelope Protection, Icing and Non-Icing Conditions; High Incidence Protection

<RULE> DEPARTMENT OF TRANSPORTATION <SUBAGY>Federal Aviation Administration</SUBAGY> <CFR>14 CFR Part 25</CFR> <DEPDOC>[Docket No. No. FAA-2021-1032; Special Conditions No. 25-854-SC]</DEPDOC> <SUBJECT>Special Conditions: Airbus Model A321neo XLR Airplanes; Flight Envelope Protection, Icing and Non-Icing Conditions; High Incidence Protection</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Federal Aviation Administration (FAA), DOT. <HD SOURCE="HED">ACTION:</HD> Final special conditions. <SUM> <HD SOURCE="HED">SUMMARY:</HD> These special conditions are issued for the Airbus Model A321neo XLR airplane. This airplane will have a novel or unusual design feature when compared to the state of technology envisioned in the applicable airworthiness standards for transport category airplanes. This design feature is flight-envelope protections, in icing and non-icing conditions, that use high-incidence protection and an alpha-floor system to automatically advance throttles when the airplane angle of attack reaches a predetermined value. 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. </SUM> <DATES> <HD SOURCE="HED">DATES:</HD> Effective June 17, 2024. </DATES> <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Troy Brown, Performance and Environment Unit, AIR-621A, Technical Policy Branch, Policy and Standards Division, Aircraft Certification Service, Federal Aviation Administration, 1801 S Airport Rd., Wichita, KS 67209-2190; telephone and fax 405-666-1050; email <E T="03">troy.a.brown@faa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> <HD SOURCE="HD1">Background</HD> 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 take-off weight of 222,000 pounds. <HD SOURCE="HD1">Type Certification Basis</HD> Under the provisions of 14 CFR 21.101, Airbus must show that the Model A321neo XLR airplane meets 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 T="03">e.g.,</E> 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 § 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 § 21.101. In addition to the applicable airworthiness regulations and special conditions, the Airbus Model A321neo XLR airplane 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 § 11.19, in accordance with § 11.38, and they become part of the type certification basis under 14 CFR 21.101. <HD SOURCE="HD1">Novel or Unusual Design Feature</HD> The Airbus Model A321neo XLR airplane will incorporate the following novel or unusual design feature: Flight-envelope protections, in icing and non-icing conditions, that use high- incidence protection and an alpha-floor function to automatically advance throttles when the airplane angle of attack (AoA) reaches a predetermined value. <HD SOURCE="HD1">Discussion</HD> The current airworthiness standards do not contain adequate safety standards for the high-incidence protection system and the alpha-floor system for the Airbus Model A321neo XLR series airplanes. This is because the FAA's current standards were designed for more traditional electronic flight control systems (EFCS), which involve less advanced envelope protections, such as stick shakers and pushers. These special conditions address the more advanced flight envelope protections, including icing and non-icing conditions, that are part of the EFCS design of the A321neo XLR airplane. The high-incidence protection system prevents the airplane from stalling and, therefore, the stall warning system is not needed during normal flight conditions. However, during failure conditions which are not shown to be extremely improbable, the requirements of §§ 25.203 and 25.207 apply, although slightly modified by these conditions. If there are failures not shown to be extremely improbable, the flight characteristics at the angle-of-attack for C <E T="52">LMAX</E> must be suitable in the traditional sense, and stall warning must be provided in a conventional manner. These special conditions address the need for modification during icing conditions and non-icing conditions. The alpha-floor function automatically advances the throttles on the operating engines under flight circumstances of low speed if the airplane reaches a predetermined high AoA. This function is intended to provide increased climb capability. These special conditions address this novel or unusual design feature on the Airbus Model A321neo XLR and 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. <HD SOURCE="HD1">Discussion of Comments</HD> The FAA issued Notice of Special Conditions No. 25-23-03-SC for the Airbus Model A321neo XLR airplane. They were published in the <E T="04">Federal Register</E> on November 3, 2023 (88 FR 75513). The FAA received comments from Airbus Commercial Aircraft (Airbus) and The Boeing Company (Boeing). Boeing requested that the FAA add statements to sections (e)(1)(ii)(B) and (C) of the proposed special conditions regarding the demonstration of satisfactory lateral control at the aft stop and the consideration of rapid application of go-around power or thrust. Boeing requested these changes for consistency with the proposed regulatory material for § 25.202(d)(2) and (4) in the Flight Test Harmonization Working Group Phase 2 Rev A Final Report  <SU>1</SU> <FTREF/> (FTHWG Report). The FAA does not agree to this change. The FAA has previously published special conditions on this subject. The terms of those special conditions were consistent with the terms of these special conditions, and the FAA finds that they provide an adequate level of safety, <E T="03">i.e.,</E> a level equivalent to the standards that, absent these special conditions, would otherwise be applicable. <FTNT> <SU>1</SU>   <E T="03">https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/09%20-%20FTHWG_Final_Report_Phase_2_RevA__Apr_2017.pdf.</E> </FTNT> Boeing recommended the FAA add “and emergency” to the proposed special conditions regarding the alpha-floor setting not interfering with normal maneuvering because this change would be consistent with proposed regulatory material for § 25.144(a) in the FTHWG Report. The FAA declines to make this change. This special condition only addresses the alpha-floor setting in normal maneuvering. The general limiting special conditions  <SU>2</SU> <FTREF/> for the A321neo XLR already include requirements for normal and emergency operations of all flight envelope protection functions, which include the alpha-floor function. <FTNT> <SU>2</SU>  88 FR 12133 (Feb. 27, 2023). </FTNT> Boeing requested the FAA revise the deceleration rate in icing conditions in section (e)(1)(ii)(C)( <E T="03">2</E> ) of the proposed special conditions to 3 knots per second because this change would be consistent with the Airbus Model A350-900 Special Conditions No. 25-517-SC part I section 5.1(b)(3)(ii) and the proposed regulatory material for § 25.202(d)(4) in the FTHWG Report. The FAA does not concur with Boeing's request because this change would not be appropriate for the design of the A321neo XLR. The XLR EFCS architecture is based on a previously certified architecture for the Airbus Model A321neo ACF. The A321neo ACF used a deceleration rate in icing conditions of 2 knots per second; therefore, using the same requirement for the A321neo XLR is appropriate and provides an adequate (equivalent) level of safety. Boeing requested the FAA revise section (e)(2)(i)(D) of the proposed special conditions related to buffeting to have the same requirement for icing and non-icing conditions, which Boeing said would also be consistent with 25-517-SC part II section 3(a)(2)(i) and the proposed regulatory material for 25.105(a)(2)(iii) in the FTHWG Report. Boeing stated that the requirement for icing conditions appears to indicate that buffet of a deterrent magnitude and severity would be acceptable for demonstration. The FAA does not concur with Boeing's request. The FAA does not intend the buffeting requirement for icing conditions to allow deterrent buffet. The wording of these special conditions is appropriate because the magnitude of the buffet can be a driver in setting the protections while still requiring the airplane be free from excessive vibration and buffet. Therefore, these special conditions provide an adequate level of safety. Boeing requested that the FAA remov ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 33k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━