
[Federal Register Volume 88, Number 156 (Tuesday, August 15, 2023)]
[Rules and Regulations]
[Pages 55359-55362]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-17403]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2023-1467; Special Conditions No. 25-840-SC]


Special Conditions: The Boeing Company Model 737-10 Airplane; 
Dynamic Test Requirements for Single Occupant Oblique Seats With or 
Without Airbags and/or 3-Point Restraints

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 Boeing Company 
(Boeing) Model 737-10 series airplane. This airplane 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 oblique (side-facing) single-occupant 
seats equipped with airbag devices or 3-point restraints. 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 Boeing on August 15, 2023. Send 
comments on or before September 29, 2023.

ADDRESSES: Send comments identified by Docket No. FAA-2023-1467 using 
any of the following methods:
     Federal eRegulations Portal: Go to https://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

[[Page 55360]]

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 https://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: John Shelden, 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 and fax 
206-231-3214; email [email protected].

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

    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 John Shelden, 
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 and fax 206-231-3214; email [email protected]. 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 and will consider comments filed late if it is possible to do 
so without incurring delay. The FAA may change these special conditions 
based on the comments received.

Background

    On October 28, 2022, Boeing applied for a change to Type 
Certificate No. A16WE for the installation of oblique (side-facing) 
passenger seats with or without airbag devices or 3-point restraints in 
the Boeing Model 737-10 series airplanes. The Boeing Model 737-10 
series airplanes are twin-engine, transport category airplanes with a 
maximum certified passenger capacity of up to 230, and a maximum 
takeoff weight of approximately 197,900 lbs.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 737-10 series airplanes, 
as changed, continue to meet the applicable provisions of the 
regulations listed in Type Certificate No. A16WE 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 Boeing Model 737-10 series 
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, the special conditions would also apply to the 
other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Boeing Model 737-10 series airplane 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

    The Boeing Model 737-10 series airplane will incorporate a seating 
configuration that is novel or unusual due to the installation of 
oblique (side-facing) passenger seats and surrounding furniture that 
introduces occupant alignment and loading concerns. These oblique seats 
may be installed at an angle of 18 to 45 degrees to the aircraft 
centerline and may include a 3-point restraint system and/or airbags, 
for occupant restraint and injury protection.

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 Boeing Model 737-10 airplane seat installation is 
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 system, or both.

[[Page 55361]]

In order to provide a level of safety that is 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. FAA-sponsored research has 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 
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.
    As noted in the special conditions for each airbag restraint 
system, because an airbag restraint system is essentially a single use 
device, there is the potential that it could deploy under crash 
conditions that are not sufficiently severe as to require head injury 
protection from the airbag restraint system. Since an actual crash is 
frequently composed of a series of impacts before the airplane comes to 
rest, this could render the airbag restraint system useless if a larger 
impact follows the initial impact. This situation does not exist with 
energy absorbing pads or upper torso restraints, which tend to provide 
protection according to the severity of the impact. Therefore, the 
installation of the airbag restraint system should be such that the 
airbag restraint system will provide protection when it is required, 
and will not expend its protection when it is not needed.
    Because these airbag restraint systems may or may not activate 
during various crash conditions, the injury criteria listed in these 
special conditions and in Sec.  25.562 must be met in an event that is 
slightly below the activation level of the airbag restraint system. If 
an airbag restraint system is included with the oblique seats, the 
system must meet the requirements in one of the airbag (inflatable 
restraint) special conditions applicable to the Boeing Model 737 series 
airplanes. These special conditions supplement part 25 and, more 
specifically, supplement Sec. Sec.  25.562 and 25.785.
    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 
Boeing Model 737-10 series airplane. Should Boeing apply at a later 
date for a change to the type certificate to include another 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 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

0
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 Boeing Company Model 737-10 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:

1. Head Injury Criteria (HIC)

    Compliance with Sec.  25.562(c)(5) is required, except that, if the 
anthropomorphic test dummy (ATD) has no apparent contact with the seat/
structure but has contact with an airbag, a HIC unlimited score in 
excess of 1000 is acceptable, provided the HIC15 score (calculated in 
accordance with 49 CFR 571.208) for that contact is less than 700.

2. Body-to-Wall/Furnishing Contact

    If a seat is installed aft of 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 
different yaw angles could result in different airbag device 
performance, then additional analysis or separate tests may be 
necessary to evaluate performance.

3. Neck Injury Criteria

    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 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:

    i. Fzc = 1530 lbs. for tension
    ii. Fzc = 1385 lbs. for compression
    iii. Myc = 229 lb-ft in flexion
    iv. 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.

4. Spine and Torso Injury Criteria

    a. The lumbar spine tension (Fz) cannot exceed 1200 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 (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.

5. Pelvis Criteria

    Any part of the load-bearing portion of the bottom of the ATD 
pelvis must not translate beyond the edges of the

[[Page 55362]]

seat bottom seat-cushion supporting structure.

6. 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.

7. 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 Lumbar 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: Boeing 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, is 
acceptable to the FAA.

8. Inflatable Airbag Restraint Systems Special Conditions

    If inflatable airbag restraint systems are installed, the airbag 
systems must meet the requirements in special conditions 25-386-SC, or 
other airbag system special conditions which are applicable to the 
Boeing Model 737 series airplanes.

    Issued in Des Moines, WA, on August 9, 2023.
Paul R. Siegmund,
Acting Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2023-17403 Filed 8-14-23; 8:45 am]
BILLING CODE 4910-13-P


