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[Federal Register Volume 89, Number 240 (Friday, December 13, 2024)]
[Rules and Regulations]
[Pages 100727-100730]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-29442]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2024-2387; Special Conditions No. 25-871-SC]

Special Conditions: Airbus Models A321 neo ACF and A321 neo XLR; 
Single-Occupant Oblique Seats With Pretensioner Restraint Systems

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

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SUMMARY: These special conditions are issued for the Airbus Model A321 
neo ACF and A321 neo XLR airplanes. These airplanes 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 incorporates oblique (side-facing) 
passenger seats which may include a 3-point restraint system with 
pretensioner. These oblique seats may be installed at an angle of 18 to 
45 degrees to the aircraft centerline and have surrounding furniture 
that introduces occupant and loading concerns. 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: This action is effective on Airbus S.A.S. on December 13, 2024. 
Send comments on or before January 27, 2025.

ADDRESSES: Send comments identified by Docket No. FAA-2024-2387 using 
any of the following methods:
     Federal eRegulations Portal: Go to 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.
    Docket: Background documents or comments received may be read at 
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, Cabin Safety Section, 
AIR-624, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service, Federal Aviation Administration, 2200 
South 216th Street, Des Moines, Washington 98198; telephone (206) 231-
3209; fax (206) 231-3827; email [email protected].

SUPPLEMENTARY INFORMATION: The substance of these special conditions 
has been published in the Federal

[[Page 100728]]

Register for public comment in several prior instances with no 
substantive comments received. Therefore, the FAA finds, pursuant to 14 
CFR 11.38(b), that new comments are unlikely, and notice and comment 
prior to this publication are unnecessary.

Privacy

    Except for Confidential Business Information (CBI) as described in 
the following paragraph, and other information as described in title 
14, Code of Federal Regulations (14 CFR) 11.35, the FAA will post all 
comments received without change to www.regulations.gov, including any 
personal information you provide. The FAA will also post a report 
summarizing each substantive verbal contact received about these 
special conditions.

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 
these special conditions contain commercial or financial information 
that is customarily treated as private, that you actually treat as 
private, and that is relevant or responsive to these special 
conditions, 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 these special conditions. Send 
submissions containing CBI to the individual listed in the For Further 
Information Contact section above. Comments the FAA receives, which are 
not specifically designated as CBI, will be placed in the public docket 
for these special conditions.

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 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 23, 2024, Airbus S.A.S. applied for an amendment to 
Type Certificate No. (TC no.) A28NM to include new Models A321 neo ACF 
and A321 neo XLR airplanes. Airbus Model A321 neo ACF and Model A321 
neo XLR airplanes, which are derivatives of the Model A321 currently 
approved under TC no. A28NM, are twin-engine transport category 
airplanes with a maximum passenger capacity of 244. The maximum takeoff 
weight of the Airbus Model A321 neo ACF is approximately 213,848 
pounds, while the Airbus Model A321 neo XLR has a maximum takeoff 
weight of approximately 222,667 pounds.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Airbus S.A.S must show that Models A321 neo ACF and A321 
neo XLR airplanes, as changed, continue to meet the applicable 
provisions of the regulations listed in TC 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 Models A321 neo ACF and 
A321 neo 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, Airbus Models A321 neo ACF and A321 neo XLR airplanes must 
comply with the 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 Features

    Airbus Models A321 neo ACF and A321 neo XLR airplanes will 
incorporate a novel or unusual design feature: single occupant oblique 
(side-facing) passenger seats that may include a 3-point restraint 
system with pretensioner. These oblique seats may be installed at an 
angle of 18 to 45 degrees relative to the aircraft centerline and have 
surrounding furniture that introduces occupant and loading concerns.

Discussion

    Title 14, Code of Federal Regulations (14 CFR) 25.785(d) requires 
that each occupant of a seat that makes more than an 18 degree angle 
with the vertical plane containing the airplane centerline must be 
protected from head injury by a safety belt and an energy absorbing 
rest that will support the arms, shoulders, head, and spine, or by a 
safety belt and shoulder harness that will prevent the head from 
contacting any injurious object.
    The proposed Airbus Model A321 neo ACF and A321 neo XLR seat 
installations are novel in that the current requirements do not 
adequately address protection of the occupant's neck and spine for 
seating configurations that are positioned at angles greater than 18 
degrees up to and including 45 degrees from the airplane centerline. 
The installation of passenger seats at angles of 18 to 45 degrees to 
the airplane centerline is unique due to the seat/occupant interface 
with the surrounding furniture that introduces occupant alignment/
loading concerns with or without the installation of a 3-point or 
airbag restraint systems. The existing special conditions for Airbus 
Model A321 neo ACF series airplane oblique seat installations (Special 
Conditions No. 25-779-SC) also do not address oblique seats with 3-
point restraint systems equipped with pretensioners. Therefore, in 
order to provide a level of safety equivalent to that afforded to 
occupants of forward and aft facing seating, additional airworthiness 
standards in the form of new special conditions are necessary.
    The FAA has been conducting and sponsoring research on appropriate 
injury criteria for oblique (side-facing) seat installations. To 
reflect current research findings, the FAA issued Policy Statement PS-
AIR-25-27, ``Technical Criteria for Approving Side-Facing Seats,'' 
dated July 11, 2018, which defines injury criteria for oblique seats.
    FAA-sponsored research has found that an un-restrained flailing of 
the

[[Page 100729]]

upper torso, even when the pelvis and torso are nearly aligned, can 
produce serious spinal and torso injuries. At lower impact severities, 
even with significant misalignment between the torso and pelvis, these 
injuries did not occur. Tests with an FAA H-III anthropomorphic test 
dummy (ATD) have identified a level of lumbar spinal tension 
corresponding to the no-injury impact severity. This level of tension 
is included as a limit in the special conditions. The spine tension 
limit selected is conservative with respect to other aviation injury 
criteria since it corresponds to a no-injury loading condition.
    Other restraint systems, in lieu of single lap belt restraint 
systems have been used to comply with the occupant injury criteria of 
Sec.  25.562(c)(5). For instance, shoulder harnesses have been widely 
used on flight-attendant seats, flight-deck seats, in business jets, 
and in general-aviation airplanes to reduce occupant head injury in the 
event of an emergency landing. Special conditions, pertinent 
regulations, and published guidance exist that relate to other 
restraint systems. However, the use of pretensioners in the restraint 
system on transport category airplane seats to comply with the occupant 
injury criteria of Sec.  25.562(c)(5) is a novel design.
    Pretensioner technology involves a step-change in loading 
experienced by the occupant for impacts below and above that at which 
the device deploys, because activation of the shoulder harness, at the 
point at which the pretensioner engages, interrupts upper-torso 
excursion. Such excursion could result in the head-injury criteria 
(HIC) being higher at an intermediate impact condition than that 
resulting from the maximum impact condition corresponding to the test 
conditions specified in Sec.  25.562. See condition 7 in these special 
conditions.
    The ideal triangular maximum-severity pulse is defined in Advisory 
Circular (AC) 25.562-1B, ``Dynamic Evaluation of Seat Restraint Systems 
and Occupant Protection on Transport Airplanes''. For the evaluation 
and testing of less-severe pulses for purposes of assessing the 
effectiveness of the pretensioner setting, a similar triangular pulse 
should be used with acceleration, rise time, and velocity change scaled 
accordingly. The magnitude of the required pulse should not deviate 
below the ideal pulse by more than 0.5g until 1.33 t1 is reached, where 
t1 represents the time interval between 0 and t1 on the referenced 
pulse shape, as shown in AC 25.562-1B. This is an acceptable method of 
compliance to the test requirements of the special conditions.
    Additionally, the pretensioner might not provide protection, after 
actuation, during secondary impacts. Therefore, the case where a small 
impact is followed by a large impact should be addressed. If the 
minimum deceleration severity at which the pretensioner is set to 
deploy is unnecessarily low, the protection offered by the pretensioner 
may be lost by the time a second, larger impact occurs.
    Conditions 1 through 7 address occupant protection in consideration 
of the oblique-facing seats. Conditions 8 through 10 ensure that the 
pretensioner system activates when intended and protects a range of 
occupants under various accident conditions. Conditions 11 through 16 
address maintenance and reliability of the pretensioner system, 
including any outside influences on the mechanism, to ensure it 
functions as intended.
    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.

Applicability

    As discussed above, these special conditions are applicable to the 
Airbus Model A321 neo ACF and Model A321 neo XLR airplanes. Should 
Airbus S.A.S. apply at a later date for a change to the type 
certificate to include another model incorporating 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 apply to that 
model as well.

Conclusion

    This action affects only a certain novel or unusual design feature 
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, and 
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 the Airbus Model A321 neo ACF and A321 
neo XLR series airplanes.
    In addition to the requirements of Sec.  25.562, passenger seats 
installed at an angle between 18 degrees and 45 degrees from the 
aircraft centerline must meet the following conditions:
    1. Body-to-Wall and Body-to-Furnishing Contact:
    If a seat is installed aft of a structure (e.g., interior wall or 
furnishings) that does not provide a homogenous contact surface for the 
expected range of occupants and yaw angles, then additional analysis 
and tests may be required to demonstrate that the injury criteria are 
met for the area that an occupant could contact. For example, if, in 
addition to a pretensioner restraint system, an airbag device is 
present, different yaw angles could result in different airbag-device 
performance, then additional analysis or separate tests may be 
necessary to evaluate performance.
    2. Neck Injury Criteria:
    The seating system must protect the occupant from experiencing 
serious neck injury. In addition to a pretensioner restraint system, if 
an airbag device also is present, the assessment of neck injury must be 
conducted with the airbag device activated, unless there is reason to 
also consider that the neck injury potential would be higher for 
impacts below the airbag-device deployment threshold.
    (a) The Nij (calculated in accordance with 49 CFR 571.208) must be 
below 1.0, where Nij = Fz/Fzc + My/Myc, and Nij critical values are:

(1) Fzc = 1530 lbs. for tension
(2) Fzc = 1385 lbs. for compression
(3) Myc = 229 lb-ft in flexion
(4) Myc = 100 lb-ft in extension

    (b) In addition, peak Fz must be below 937 lbs. in tension and 899 
lbs. in compression.
    (c) Rotation of the head about its vertical axis relative to the 
torso is limited to 105 degrees in either direction from forward 
facing.
    (d) The neck must not impact any surface that would produce 
concentrated loading on the neck.
    3. Spine and Torso Injury Criteria:
    (a) The lumbar spine tension (Fz) cannot exceed 1,200 lbs.
    (b) Significant concentrated loading on the occupant's spine, in 
the area between the pelvis and shoulders during impact, including 
rebound, is not acceptable. During this type of contact, the interval 
for any rearward (X direction) acceleration exceeding 20g must be less 
than 3 milliseconds as measured by the thoracic instrumentation 
specified in 49 CFR part 572, subpart E, filtered in accordance with 
SAE International

[[Page 100730]]

(SAE) recommended practice J211/1, ``Instrumentation for Impact Test-
Part 1-Electronic Instrumentation.''
    (c) The occupant must not interact with the armrest or other seat 
components in any manner significantly different than would be expected 
for a forward-facing seat installation.
    4. Pelvis Criteria:
    Any part of the load-bearing portion of the bottom of the ATD 
pelvis must not translate beyond the edges of the seat bottom seat-
cushion supporting structure.
    5. Femur Criteria:
    Axial rotation of the upper leg (about the Z-axis of the femur per 
SAE Recommended Practice J211/1) must be limited to 35 degrees from the 
nominal seated position. Evaluation during rebound does not need to be 
considered.
    6. ATD and Test Conditions:
    Longitudinal tests conducted to measure the injury criteria above 
must be performed with the FAA Hybrid III ATD, as described in SAE 
1999-01-1609, ``A Lumber Spine Modification to the Hybrid III ATD for 
Aircraft Seat Tests.'' The tests must be conducted with an undeformed 
floor, at the most-critical yaw cases for injury, and with all lateral 
structural supports (e.g. armrests or walls) installed.

    Note: The applicant must demonstrate that the installation of 
seats via plinths or pallets meets all applicable requirements. 
Compliance with the guidance contained in policy memorandum PS-ANM-
100-2000-00123, ``Guidance for Demonstrating Compliance with Seat 
Dynamic Testing for Plinths and Pallets,'' dated February 2, 2000, 
may be applied.

    7. Head Injury Criteria:
    The HIC value must not exceed 1000 at any condition at which the 
pretensioner does or does not deploy, up to the maximum severity pulse 
that corresponds to the test conditions specified in Sec.  25.562. 
Tests must be performed to demonstrate this, taking into account any 
necessary tolerances for deployment.
    When an airbag is present in addition to the pretensioner restraint 
system, and the anthropomorphic test dummy (ATD) has no apparent 
contact with the seat/structure but has contact with the airbag, a HIC 
unlimited score in excess of 1000 is acceptable provided the HIC15 
score (calculated in accordance with 49 CFR 571.208) for the contact is 
less than 700. ATD head contact with the seat or other structure, 
through the airbag, or contact subsequent to contact with the airbag, 
requires a HIC value that does not exceed 1000.
    8. Protection During Secondary Impacts:
    The pretensioner activation setting must be demonstrated to 
maximize the probability of the protection being available when needed, 
considering secondary impacts.
    9. Protection of Occupants Other than 50th Percentile:
    Protection of occupants for a range of stature from a 2-year-old 
child to a 95th percentile male must be shown. For shoulder harnesses 
that include pretensioners, protection of occupants other than a 50th 
percentile male may be shown by test or analysis. In addition, the 
pretensioner must not introduce a hazard to passengers due to the 
following seat configurations:
    (a) The seat occupant is holding an infant.
    (b) The seat occupant is a child in a child-restraint device.
    (c) The seat occupant is a pregnant woman.
    10. Occupants Adopting the Brace Position:
    Occupants in the traditional brace position when the pretensioner 
activates must not experience adverse effects from the pretensioner 
activation.
    11. Inadvertent Pretensioner Actuation:
    (a) The probability of inadvertent pretensioner actuation must be 
shown to be extremely remote (i.e., average probability per flight hour 
of less than 10-7).
    (b) The system must be shown not susceptible to inadvertent 
pretensioner actuation as a result of wear and tear, or inertia loads 
resulting from in-flight or ground maneuvers likely to be experienced 
in service.
    (c) The seated occupant must not be seriously injured as a result 
of inadvertent pretensioner actuation.
    (d) Inadvertent pretensioner activation must not cause a hazard to 
the airplane, nor cause serious injury to anyone who may be positioned 
close to the retractor or belt (e.g., seated in an adjacent seat or 
standing adjacent to the seat).
    12. Availability of the Pretensioner Function Prior to Flight:
    The design must provide means for a crewmember to verify the 
availability of the pretensioner function prior to each flight, or the 
probability of failure of the pretensioner function must be 
demonstrated to be extremely remote (i.e., average probability per 
flight hour of less than 10-7) between inspection intervals.
    13. Incorrect Seat Belt Orientation:
    The system design must ensure that any incorrect orientation 
(twisting) of the seat belt does not compromise the pretensioner 
protection function.
    14. Contamination Protection:
    The pretensioner mechanisms and controls must be protected from 
external contamination associated with that which could occur on or 
around passenger seating.
    15. Prevention of Hazards:
    The pretensioner system must not induce a hazard to passengers in 
case of fire, nor create a fire hazard, if activated.
    16. Functionality After Loss of Power:
    The system must function properly after loss of normal airplane 
electrical power, and after a transverse separation in the fuselage at 
the most critical location. A separation at the location of the system 
does not have to be considered.

    Issued in Kansas City, Missouri, on December 9, 2024.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2024-29442 Filed 12-12-24; 8:45 am]
BILLING CODE 4910-13-P
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