[Federal Register Volume 89, Number 91 (Thursday, May 9, 2024)]
[Rules and Regulations]
[Pages 39566-39569]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-10075]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2024-0566; Special Conditions No. 25-861-SC]


Special Conditions: The Boeing Model 737-8 Airplane; Dynamic Test 
Requirements for Single-Occupant Oblique Seats With 3-Point Seat Belt 
With Pretensioner

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 737-8 series airplane. This airplane, as modified by 
HAECO Cabin Solutions, LLC. (HAECO), 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 single-occupant oblique (side-facing) seats equipped 
with a 3-point seat belt with pretensioner. 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 HAECO on May 9, 2024. Send comments 
on or before June 24, 2024.

ADDRESSES: Send comments identified by Docket No. FAA-2024-0566 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, 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: 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

[[Page 39567]]

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 
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 these 
proposed special conditions. Send submissions containing CBI to the 
individual listed in the For Further Information Contact section below. 
Comments the FAA receives, which are not specifically designated as 
CBI, will be placed in the public docket for these proposed 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 December 20, 2022, HAECO applied for a supplemental type 
certificate for the installation of oblique (side-facing) passenger 
seats that incorporate a 3-point restraint with pretensioner system in 
Boeing Model 737-8 series airplanes. The Boeing Model 737-8 series 
airplane is a twin-engine, transport category airplane with a maximum 
passenger capacity of 189, and a maximum takeoff weight of 
approximately 182,200 pounds.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, HAECO must show that the Model 737-8 series airplane, 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 737-8 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 737-8 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 737-8 series airplane, as modified by HAECO, will 
incorporate a novel or unusual design feature which is the installation 
of 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 alignment 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 Boeing Model 737-8 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 restraint system.
    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, ``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 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

[[Page 39568]]

corresponds to a no-injury loading condition.
    Other 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 relate to other restraint 
systems. However, the use of pretensioners in the restraint system on 
transport-airplane seats 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.
    The existing special conditions for Boeing Model 737-8 series 
airplane oblique seat installations do not address oblique seats with 
3-point restraint systems equipped with pretensioners. Therefore, the 
proposed configuration requires special conditions.
    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 
Boeing Model 737-8 series airplane, modified by HAECO. Should HAECO 
apply at a later date for a supplemental type certificate to modify any 
other model included on Type Certificate No. A16WE 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 and affects only the applicant who applied to the FAA for 
approval of these features on the airplane.

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 Boeing Company Model 737-8 series 
airplanes, modified by HAECO.
    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/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 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.''

[[Page 39569]]

    (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 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:  HAECO 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.

7. Head Injury Criteria (HIC)

    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.

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 because 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 because 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 May 3, 2024.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2024-10075 Filed 5-8-24; 8:45 am]
BILLING CODE 4910-13-P