[Federal Register Volume 87, Number 66 (Wednesday, April 6, 2022)]
[Proposed Rules]
[Pages 19811-19813]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-07228]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2021-0891; Notice No. 25-21-04-SC]


Special Conditions: Airbus Model A321neoXLR Airplane; Passenger 
Protection From External Fire

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This action proposes special conditions for the Airbus Model 
A321neoXLR airplane. This airplane will have a novel or unusual design 
feature when compared to the technology envisaged by the airworthiness 
standards for transport category airplanes. This design feature is an 
integral rear center tank (RCT). 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 comments on or before May 23, 2022.

ADDRESSES: Send comments identified by Docket No. FAA-2021-0891 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 or 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 9 a.m. and 5 p.m., Monday 
through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: Except for Confidential Business Information (CBI) as 
described in the following paragraph, and other information as 
described in 14 CFR 11.35, the FAA will post all comments received 
without change to http://www.regulations.gov/, including any personal 
information you provide. The FAA will also post a report summarizing 
each substantive verbal contact received about this proposal.
    Confidential Business Information: Confidential Business 
Information (CBI) is commercial or financial information that is both 
customarily and actually treated as private by its owner. Under the 
Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from 
public disclosure. If your comments responsive to this Notice contain 
commercial or financial information that is customarily treated as 
private, that you actually treat as private, and that is relevant or 
responsive to this Notice, it is important that you clearly designate 
the submitted comments as CBI. Please mark each page of your submission 
containing CBI as ``PROPIN.'' The FAA will treat such marked 
submissions as confidential under the FOIA, and the indicated comments 
will not be placed in the public docket of this Notice. Submissions 
containing CBI should be sent to Shannon Lennon, Human Machine 
Interface, AIR-626, Technical Innovation Policy Branch, Policy and 
Innovation Division, Aircraft Certification Service, Federal Aviation 
Administration, 2200 South 216th Street, Des Moines, Washington 98198; 
telephone and fax 206-231-3209; email [email protected]. Comments 
the FAA receives, which are not specifically designated as CBI, will be 
placed in the public docket for this rulemaking.
    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 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: Shannon Lennon, Human Machine 
Interface, AIR-626, Technical Innovation Policy Branch, Policy and 
Innovation Division, Aircraft Certification Service, Federal Aviation 
Administration, 2200 South 216th Street, Des Moines, Washington 98198; 
telephone and fax 206-231-3209; email [email protected].

SUPPLEMENTARY INFORMATION: 

Comments Invited

    The FAA invites 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

[[Page 19812]]

recommended change, and include supporting data.
    The FAA will consider all comments received by the closing date for 
comments. The FAA may change these special conditions based on the 
comments received.

Background

    On September 16, 2019, Airbus applied for an amendment to Type 
Certificate No. A28NM to include the new Model A321neoXLR airplane. The 
Model A321neoXLR airplane, which is a derivative of the Model 
A321neoACF airplane currently approved under Type Certificate No. 
A28NM, is a twin-engine transport category aircraft that seats 244 
passengers and has a maximum takeoff weight of 202,000 lbs.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Airbus must show that the Model A321neoXLR 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.g., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the Airbus Model A321NeoXLR airplane 
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 A321NeoXLR 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 14 CFR 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 Feature

    The Airbus Model A321NeoXLR airplane will incorporate the following 
novel or unusual design feature:
    An integral RCT.

Discussion

    The proposed Airbus Model A321neoXLR incorporates an integral RCT. 
This tank is a ``center'' fuel tank, in that would, if approved, be 
located in the airplane fuselage rather than in its wings. The tank is 
a ``rear'' tank, that would be located aft of the wheel bay; it would 
be in an area of the lower fuselage that partially replaces the aft 
cargo compartment of the airplane from which this proposed model is 
derived. The top of the tank would be directly below the floor of the 
passenger cabin. The fuel tank would be ``integral'' to the airplane, 
in that its walls would be part of the airplane structure. The exterior 
skin of the airplane fuselage would constitute part of the walls of the 
fuel tank, and these areas would lack the thermal/acoustic insulation 
that usually lines the exterior skin of an airplane fuselage.
    This proposed design was not envisaged by the FAA's regulatory 
requirements for insulation installations on transport category 
airplanes. 14 CFR 25.856(b) requires all thermal/acoustic insulation in 
the lower half of the airplane fuselage and their installation to 
comply with the flame penetration resistance test of Appendix F Part 
VII. The FAA adopted Sec.  25.856(b) to raise the level of post-crash 
fire safety on transport category airplanes. Part VII of Appendix F 
requires a stringent test method for all thermal/acoustic insulation 
proposed for installation in the lower half of the fuselage. The FAA's 
intent in imposing this requirement was to ensure that this insulation 
provides an additional barrier between the occupants and an external 
post-crash fire, especially a fire resulting from a pool of spilled 
aviation fuel.\1\ This barrier extends the time available for 
evacuation.
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    \1\ See pg. 2 of FAA Advisory Circular 25.856-2A, Installation 
of Thermal/Acoustic Insulation for Burnthrough Protection (Jul. 29, 
2008), available at drs.faa.gov.
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    While the rule applies to the thermal/acoustic insulation that an 
applicant proposes as part of their design, it does not require 
applicants to install such insulation. Since the fuselage skins of the 
lower half of transport category airplanes are generally insulated, and 
were at the time these standards were developed, the FAA considered 
this approach to be sufficient to ensure safety. The rulemaking also 
noted, however, that if applicants began to propose designs that 
omitted this thermal/acoustic insulation, the FAA would revisit the 
need for a specific fuselage burnthrough standard.\2\
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    \2\ Improved Flammability Standards for Thermal/Acoustic 
Insulation Materials Used In Transport Category Airplanes, 68 FR 
45046, 45049 (Jul. 31, 2003).
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    Thus, since this proposed design will lack thermal/acoustic 
insulation under the fuselage skin in the area of the fuel tank, 
current FAA regulations do not ensure that it will provide a continuous 
flame penetration (burnthrough) resistant barrier between the 
passengers and an external fire, nor that it will provide enough 
protection, against an external post-crash fire, to allow time for 
passengers to evacuate.
    According to Airbus, its proposed design does not allow for 
compliant thermal/acoustic insulation to be placed beneath the cabin 
floor. This large volume of unheated liquid (fuel), directly below the 
floor of the passenger cabin, would, without mitigation, create a `cold 
feet' effect for the passengers above it. Therefore, Airbus plans to 
install insulation panels between the fuel tank and the cabin floor, 
for comfort reasons. These insulation panels would normally be required 
to meet Sec.  25.856(b). However, Airbus states that it is technically 
not feasible to install thermal/acoustic insulation that complies with 
Sec.  25.856(b), due to the lack of space in this area, and the need to 
keep nearby decompression panels free of blockages and ensure adequate 
ventilation.
    To address the assumption in the FAA's current flammability 
standards that proposed airplane designs would include thermal/acoustic 
insulation in the lower fuselage, and to ensure that this proposed 
design does not reduce the time available for passenger evacuation in 
the case of a post-crash external fire, special conditions are needed. 
Specifically, the FAA proposes to require that the lower half of the 
airplane fuselage, spanning the longitudinal area of the tank, be 
resistant to fire penetration. ``Resistant to fire penetration'' would, 
for this special condition, mean that this area provides fire 
penetration resistance equivalent to the resistance which would be 
provided if the fuselage were lined with thermal/acoustic insulation 
that meets the flame penetration resistance test requirements of part 
VII of Appendix F. The applicant's method of compliance may, but is not 
required to, be based upon any inherent flame penetration resistance 
capability

[[Page 19813]]

provided by the construction of the fuel tank and/or other surrounding 
features.
    The 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.

Applicability

    As discussed above, these special conditions are applicable to the 
Airbus Model A321NeoXLR airplane. Should Airbus apply at a later date 
for a change to the type certificate to include another model 
incorporating the same novel or unusual design feature, these special 
conditions would apply to that model as well.

Conclusion

    This action affects only a certain novel or unusual design feature 
on one model of airplane. 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 Proposed Special Conditions

    The Federal Aviation Administration (FAA) proposes the following 
special conditions as part of the type certification basis for Airbus 
Model A321NeoXLR airplanes.

Passenger Protection From External Fire

    The lower half of the fuselage, spanning the longitudinal location 
of the rear center fuel tank, must be resistant to fire penetration.

    Issued in Kansas City, Missouri, on April 1, 2022.
Patrick R. Mullen,
Manager, Technical Innovation Policy Branch, Policy and Innovation 
Division, Aircraft Certification Service.
[FR Doc. 2022-07228 Filed 4-5-22; 8:45 am]
BILLING CODE 4910-13-P