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[Federal Register Volume 90, Number 23 (Wednesday, February 5, 2025)]
[Rules and Regulations]
[Pages 9003-9007]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2025-02218]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2024-2570; Special Conditions No. 25-875-SC]

Special Conditions: Airbus Model A321neo ACF and A321neo XLR 
Series Airplanes; Dynamic Test Requirements for Single Occupant Oblique 
Seats at an Installation Angle of 49 Degrees With Airbags and 3-Point 
Restraint or Pretensioner Restraint Systems

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Airbus Model 
A321neo ACF and 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 a single-occupant oblique 
seat with an airbag and 3-point or pretensioner restraint system 
positioned at a 49-degree angle from the cabin centerline. 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 February 5, 2025.

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, WA 98198; telephone (206) 231-3209; 
email [email protected].

SUPPLEMENTARY INFORMATION: 

Background

    On April 6, 2022, Airbus SAS applied for an amendment to Type 
Certificate (TC) No. A28NM for the installation of a single-occupant 
oblique seat with an airbag and 3-point or pretensioner restraint 
system, positioned at a 49-degree angle from the cabin centerline in 
new Airbus Model A321neo ACF and A321neo XLR airplanes. Airbus Model 
A321neo ACF and A321neo 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 A321neo ACF is 
approximately 213,848 pounds, while the Airbus Model A321neo XLR has a 
maximum takeoff weight of approximately 222,667 pounds.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Airbus SAS must show that 
the Model A321neo ACF and A321neo 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 Airbus Model A321neo ACF and 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, Airbus Model A321neo ACF and A321neo 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 Model A321neo ACF and A321neo XLR airplanes will incorporate 
the following novel or unusual design feature: single-occupant oblique 
seats with airbag devices and 3-point restraints or a pretensioner 
restraint system installed at 49 degrees relative to the aircraft cabin 
centerline.

Discussion

    Title 14 of the CFR, Sec.  25.785(d), requires that each occupant 
of a seat installed at an angle of more than 18 degrees relative to 
airplane cabin centerline, must be protected from head injury using a 
seatbelt and an energy-absorbing rest that supports the arms, 
shoulders, head, and spine, or using a seatbelt and shoulder harness 
designed to prevent the head from contacting any injurious object.
    The Airbus Model A321neo ACF and A321neo XLR airplane's single 
occupant oblique seat installation with airbag devices and 3-point 
restraint or pretensioner restraint system is novel such that the 
current requirements do not adequately address airbag or pretensioner 
devices and protection of the occupant's neck, spine, torso, and legs 
for seating configurations that are positioned at an angle of 49 
degrees from the airplane centerline. The seating configuration 
installation angle is beyond the installation-design limits of current 
special conditions issued for seat positions at angles between 18 
degrees and 45 degrees. At angles greater than 45 degrees, lateral neck 
bending and other injury mechanisms prevalent from a fully side-facing 
installation become a concern, given the addition of oblique seat 
properties. To address these potential injury mechanisms, these special 
conditions are based on FAA Policy Statement PS-AIR-25-27, ``Technical 
Criteria for Approving Obliques Seats'' as well as Policy Statement PS-
ANM-25-03-R1, ``Technical Criteria for Approving Side-Facing Seats.''
    To provide a level of safety equivalent to that afforded to the 
occupants of forward and aft-facing seats, new special conditions 
containing additional airworthiness standards for dynamic testing 
requirements, including both the injury criteria limits from the 
oblique-seat policy and the fully side-facing seat policy, are 
necessary.
    FAA-sponsored research found that an un-restrained flailing of the 
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

[[Page 9004]]

pelvis, these injuries did not occur. Tests with an FAA H-III 
anthropomorphic test device (ATD) have identified a level of lumbar 
spinal tension corresponding to the no-injury impact severity. The FAA 
has implemented this spinal tension limit in special conditions for 
oblique seats. The spine tension limit selected by the FAA 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 restrain 
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 an 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 (a)(3) 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 with 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 (a) through (g) address occupant protection in 
consideration of the oblique-facing seats. Condition (h) addresses 
airbag systems. Conditions (i)(1) through (i)(3) ensure that the 
pretensioner system activates when intended and protects a range of 
occupants under various accident conditions. Conditions (i)(4) through 
(9) address the maintenance and reliability of the pretensioner system, 
including any outside influences on the mechanism, to ensure it 
functions as intended. Condition (j) addresses general instructions 
that supplement these special conditions when tests are required to 
assist with test set-ups and appropriate ATD selection.
    The 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. 25-24-05-
SC for the Airbus Model A321neo ACF and A321neo XLR airplanes, which 
was published in the Federal Register on December 23, 2024 (89 FR 
104455).
    The FAA received responses from two commenters: Airbus Commercial 
Aircraft (Airbus) and The Boeing Company (Boeing).
    Airbus, the applicant, requested that the FAA update paragraph 
(j)(1) of this special condition to include cross-references to the 
conditions in paragraphs (c)(5), (d)(3), and (e)(3). These conditions 
may necessitate additional tests using the ES-2re ATD.
    The FAA concurs with the comment and added the cross-references to 
paragraph (j)(1).
    Boeing requested that the FAA add a new condition to paragraph (i) 
of this special condition to ensure pretensioner exhaust is not 
hazardous to passengers, similar to the corresponding condition 
required for airbag systems.
    The FAA concurs with the comment. Certain pretensioner restraint 
systems, like airbag systems, incorporate firing mechanisms that may 
exhaust small amounts of gas and particulate when activated. The FAA 
has previously published special conditions (see Special Condition No. 
25-375-SC) to address this concern for airbags and has added a 
condition to paragraph (i)(8)(ii) to address the need to similarly 
ensure that pretensioner activation exhaust and particulate are not 
hazardous to passengers.
    Except as discussed above, the special conditions are adopted as 
proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Airbus Model A321neo ACF and A321neo XLR airplanes. 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.
    Under standard practice, the effective date of final special 
conditions would be 30 days after the date of publication in the 
Federal Register. However, as the certification date for the Airbus 
Model A321neo ACF and A321neo XLR airplanes is imminent, the FAA finds 
that good cause exists to make these special conditions effective upon 
publication.

Conclusion

    This action affects only a certain novel or unusual design feature 
on one model series 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 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 A321neo ACF and 
A321neo XLR airplanes.
    In addition to the requirements of Sec. Sec.  25.562 and 25.785, 
passenger seats with airbag devices and 3-point restraints or 
pretensioner restraints installed at an angle 49 degrees from the 
aircraft centerline must meet the following conditions:

(a) Head Injury Criteria (HIC)

    HIC assessments are required only for head contact with the seat 
and other structures.
    (1) Compliance with Sec.  25.562(c)(5) is required, except when an 
airbag device is present in addition to the 3-point restraint system 
and the anthropomorphic test dummy (ATD)

[[Page 9005]]

has no apparent contact with the seat and other structure but has 
contact with the airbag. An HIC score in excess of 1,000 is acceptable, 
provided the HIC15 score (calculated in accordance with 49 CFR 571.208) 
for that contact is less than 700.
    (2) ATD head contact with the seat or other structure, through the 
airbag (if installed), or contact subsequent to contact with the airbag 
requires an HIC value not exceeding 1,000.
    (3) The HIC value must not exceed 1,000 in any condition in which 
the airbag or pretensioner (if installed) does or does not deploy up to 
the maximum severity pulse specified by the existing requirements.
    (4) To accommodate a range of occupant heights (5th percentile 
female to 95th percentile male), any surface, airbag or otherwise, that 
provides support for the occupant's head must provide that support in a 
consistent manner regardless of occupant stature. Otherwise, additional 
HIC assessment tests may be needed.

(b) Body-to-Wall/Furnishing Contact

    If a seat is installed aft of a structure, such as an interior wall 
or furnishing 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 an occupant could contact. For example, 
different yaw angles could result in different injury considerations 
and airbag performance, and additional analysis or separate tests may 
be necessary to evaluate performance.

(c) Neck Injury Criteria

    (1) The seating system must protect the occupant from experiencing 
serious neck injury. The assessment of neck injury must be conducted 
with the airbag device activated unless there is also reason to 
consider that the neck injury potential would be higher for impacts 
below the airbag device deployment threshold.
    (2) Rotation of the head about its vertical axis, relative to the 
torso, is limited to 105 degrees in either direction from forward-
facing.
    (3) The neck must not impact any surface that would produce 
concentrated loading on the neck.
    (4) Assess neck injury for fore and aft neck bending using an FAA 
Hybrid III ATD, as described in SAE International (SAE) Technical Paper 
1999-01-1609, ``A Lumbar Spine Modification to the Hybrid III ATD for 
Aircraft Seat Tests,'' applying the following criteria:
    (i) 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:

Fzc = 1,530 lbs (6805 N) for tension
Fzc = 1,385 lbs (6160 N) for compression
Myc = 229 lb-ft (301 Nm) in flexion
Myc = 100 lb-ft (136 Nm) in extension

    (ii) In addition, peak upper-neck Fz must be below 937 lbs (4168 N) 
in tension and 899 lbs (3999 N) in compression.
    (5) When lateral neck bending is present, assess it using an ES-2re 
ATD as defined by 49 CFR part 572, subpart U. The data must be filtered 
at channel frequency class 600 as defined in SAE Recommended Practice 
J211/11, ``Instrumentation for Impact Test Part 1- Electronic 
Instrumentation.''
    (i) The upper-neck tension force at the occipital condyle (O.C.) 
location must be less than 405 lbs (1,800 N).
    (ii) The upper-neck compression force at the O.C. location must be 
less than 405 lbs (1,800 N).
    (iii) The upper-neck bending torque about the ATD x-axis at the 
O.C. location must be less than 1,018 in-lbs (115 Nm).
    (iv) The upper-neck resultant shear force at the O.C. location must 
be less than 186 lbs (825 N).

(d) Spine and Torso Injury Criteria

    (1) The seating system must protect the occupant from experiencing 
spine and torso injury. The assessment of spine and torso injury must 
be conducted with the airbag device activated unless it is necessary to 
also consider that the occupant-injury potential would be higher for 
impacts below the airbag-device deployment threshold.
    (2) Assess spine and torso injury for oblique torso bending using 
an FAA Hybrid III ATD, applying the following criteria:
    (i) The lumbar spine tension (Fz) cannot exceed 1,200 lbs (5338 N).
    (ii) 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 Recommended Practice J211/1.
    (3) When lateral torso bending is present, assess spine and torso 
injury using an ES-2re ATD, applying the following criteria:
    (i) Thoracic: The deflection of any of the ES-2re ATD upper, 
middle, and lower ribs must not exceed 1.73 inches (44 mm). Process the 
data as defined in Federal Motor Vehicle Safety Standards (FMVSS) 
571.214, title 49 of the CFR.
    (ii) Abdominal: The sum of the measured ES-2re ATD front, middle, 
and rear abdominal forces must not exceed 562 lbs (2,500 N). Process 
the data as defined in FMVSS 571.214.
    (iii) Upper-torso support: The lateral flexion of the ATD torso 
must not exceed 40 degrees from the normal upright positions during 
impact.

(e) Pelvic Criteria

    (1) The seating system must protect the occupant from experiencing 
pelvis injury.
    (2) 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.
    (3) When pelvis contact with the armrest or surrounding interior 
components is present, assess it using an ES-2re ATD. The pubic 
symphysis force measured by the ES-2re ATD must not exceed 1,350 lbs 
(6,000 N). Process the data as defined in FMVSS 571.214.

(f) Femur Criteria

    Limit axial rotations of the upper leg (about the z-axis of the 
femur, per SAE Recommended Practice J211/1) to 35 degrees from the 
nominal seated position. Evaluation during rebound does not need to be 
considered.

(g) ATD and Test Condition

    (1) Perform longitudinal tests to measure the injury criteria above 
using the FAA Hybrid III ATD or the ES-2re ATD. Conduct the tests with 
the undeformed floor, at the most critical yaw cases for injury, and 
with all lateral structural supports (e.g., armrests or walls) 
installed.
    (2) For longitudinal tests conducted in accordance with Sec.  
25.562(b)(2), show compliance with the seat-strength requirements of 
Sec.  25.562(c)(7) and (8), and these special conditions, to ensure 
proper loading of the seat by the occupant, the ATD pelvis must remain 
supported by the seat pan, and the restraint system must remain on the 
pelvis of the ATD until rebound begins. No injury criteria evaluation 
is necessary for tests conducted only to assess seat-strength 
requirements.
    (3) If a seat installation includes adjacent items that are within 
contact range of an occupant, assess the injury potential of that 
contact. To make this assessment, tests may be conducted to include the 
actual contact item, located

[[Page 9006]]

and attached in a representative fashion. Alternatively, the injury 
potential may be assessed through a combination of tests with contact 
items having the same geometry as the actual contact item but having 
stiffness characteristics that would create the worst case for injury, 
such as injuries due to both contact with the item and lack of support 
from the item.
    (4) Conduct the combined horizontal and vertical test, required by 
Sec.  25.562(b)(1) and these special conditions, with a Hybrid II ATD 
(49 CFR part 572, subpart B, as specified in Sec.  25.562) or 
equivalent.
    (5) The design and installation of seat belt buckles must prevent 
unbuckling due to applied inertial forces or impact from seat occupant 
hands and arms during an emergency landing.

(h) Inflatable Airbag-Restraint System Special Conditions (When 
Installed)

    An inflatable airbag-restraint system must meet the requirements of 
Special Conditions No. 25-375-SC, ``Airbus A318, A319, A320 and A321 
Series Airplanes Inflatable Restraints.''

(i) Pretensioner System Special Conditions (When Installed)

    (1) 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.
    (2) 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 seating configurations:
    (i) The seat occupant is holding an infant.
    (ii) The seat occupant is a child in a child-restraint device.
    (iii) The seat occupant is a pregnant woman.
    (3) Occupants Adopting the Brace Position:
    Occupants in the traditional brace position, when the pretensioner 
activates, must not experience adverse effects from the pretensioner 
activation.
    (4) Inadvertent Pretensioner Actuation:
    (i) 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).
    (ii) The system must be shown not susceptible to inadvertent 
pretensioner actuation due to wear and tear or inertia loads resulting 
from in-flight or ground maneuvers likely to be experienced in service.
    (iii) The seated occupant must not be seriously injured due to 
inadvertent pretensioner actuation.
    (iv) Inadvertent pretensioner activation must not cause a hazard to 
the airplane nor cause serious injury to anyone positioned close to the 
retractor or belt (e.g., seated in an adjacent seat or standing 
adjacent to the seat).
    (5) Availability of the Pretensioner Function Before Flight:
    The design must provide means for a crewmember to verify the 
availability of the pretensioner function before 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.)
    (6) 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.
    (7) Contamination Protection:
    The pretensioner mechanisms and controls must be protected from 
external contamination that could occur on or around passenger seating.
    (8) Prevention of Hazards:
    (i) The pretensioner system must not induce a hazard to passengers 
in case of fire, nor create a fire hazard if activated.
    (ii) The pretensioner system must not release hazardous quantities 
of gas or particulate matter into the cabin.
    (9) Functionality After Loss of Power:
    The system must function properly after the 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.

(j) General Test Instructions

    (1) The appropriate ATD to assess occupant injury (FAA Hybrid III 
or ES-2re) will be determined based on the occupant kinematics at the 
selected test angle. At the +10 degree yaw angle, the occupant 
kinematics show that occupant injury tests using both ATDs may be 
required. See the conditions in (c)(5), (d)(3), and (e)(3) when 
determining the necessity for additional tests using an ES-2re ATD.
    (2) Conduct vertical tests with the Hybrid II ATD or equivalent, 
with existing pass/fail criteria.
    (3) Conduct longitudinal structural tests with the Hybrid II ATD or 
equivalent, deformed floor, with 10 degrees yaw, and with all lateral 
structural supports (e.g., armrests or walls) required to support the 
occupant.
    (4) Conduct longitudinal occupant injury tests, as necessary, with 
the Hybrid III ATD or ES-2re ATD, or both, undeformed floor, yaw, and 
with all lateral structural supports (e.g., armrests or walls) 
critically represented which are within the contact range of the 
occupant.
    (i) Pass/fail injury assessments:
    (A) Perform HIC, fore/aft neck injury, spinal tension, and femur 
evaluations using an FAA Hybrid III ATD.
    (B) Perform lateral neck injury, thoracic, abdominal, pelvis, and 
femur evaluations using an ES-2re ATD.
    (ii) [Reserved]
    (5) For injury assessments accomplished by testing with the ES-2re 
ATD for the longitudinal test(s) conducted in accordance with Sec.  
25.562(b)(2) and these special conditions, the ATDs must be positioned, 
clothed, and have lateral instrumentation configured as follows:
    (i) ES-2re ATD Lateral Instrumentation:
    The rib-module linear slides are directional (i.e., deflection 
occurs in either a positive or negative ATD y-axis direction). Install 
the modules such that the moving end of the rib module is toward the 
front of the airplane. Install the three abdominal-force sensors so 
that they are on the side of the ATD and toward the front of the 
airplane.
    (ii) ATD Clothing:
    Clothe each ATD in form-fitting cotton stretch garments with short 
to full-length sleeves, mid-calf to full-length pants, and size 11E 
(45) shoes weighing about 2.5 lbs (1.1 kg) and having a heel height of 
about 1.5 inches (3.8 cm). The color of the clothing should be in 
contrast to the color of the restraint system and the background. The 
color of the clothing should be chosen to avoid overexposing the high-
speed images taken during the test. The ES-2re jacket is sufficient for 
torso clothing, although a form-fitting shirt may be used if desired.
    (iii) ATD Positioning:
    (A) Lower the ATD vertically into the seat while simultaneously:
    (1) Aligning the midsagittal plane (a vertical plane through the 
midline of the body; dividing the body into right and left halves) with 
approximately the middle of the seat place.
    (2) Keeping the upper legs horizontal by supporting them just 
behind the knees.
    (3) Applying a horizontal x-axis direction (in the ES-2re ATD 
coordinate system) force of about 20 lbs (89 N) to

[[Page 9007]]

the bottom rib of the ES-2re to compress the seat back cushion.
    (B) After all lifting devices have been removed from the ATD:
    (1) Rock it slightly to settle it in the seat.
    (2) Bend the knees of the ATD.
    (3) Separate the knees by about 4 inches (100 mm).
    (4) Set the ATD's head at approximately the midpoint of the 
available range of z-axis rotation (to align the head and torso 
midsagittal planes).
    (5) Position the ATD's arms at the joint's mechanical detent to 
position them to an approximately 20 to 40-degree angle with respect to 
the torso.
    (6) Position the feet such that the centerlines of the lower legs 
are approximately parallel.

    Issued in Kansas City, Missouri, on January 30, 2025.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2025-02218 Filed 2-4-25; 8:45 am]
BILLING CODE 4910-13-P
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