[Federal Register Volume 87, Number 30 (Monday, February 14, 2022)]
[Rules and Regulations]
[Pages 8147-8150]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-03012]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2021-1023; Special Conditions No. 25-811-SC]


Special Conditions: The Boeing Company, Model 737-10 Airplane; 
Dynamic Test Requirements for Single-Occupant, Oblique (Side-Facing) 
Seats Installed at 49 Degrees With Airbag Devices and 3-Point 
Restraints

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for The Boeing Company 
(Boeing) Model 737-10 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 single-occupant oblique seats with 
airbag devices and 3-point restraints, installed at 49 degrees relative 
to the airplane cabin bow-to-stern 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 14, 2022.

FOR FURTHER INFORMATION CONTACT: John Shelden, Human Machine Interface 
Section, AIR-626, Technical Innovation Policy Branch, Policy and 
Innovation Division, Aircraft Certification Service, Federal Aviation 
Administration, 2200 South 216th Street, Des Moines, Washington 98198; 
telephone and fax 206-231-3214; email [email protected].

SUPPLEMENTARY INFORMATION:

Background

    On January 30, 2019, Boeing applied for a change to Type 
Certificate No. A16WE for the installation of single-occupant oblique 
seats, with airbag devices and 3-point restraints, installed at 49 
degrees relative to the airplane cabin bow-to-stern centerline in the 
Boeing Model 737-10 airplane. The Boeing Model 737-10 airplane is a 
twin-engine, transport-category airplane with seating for 230 
passengers and a maximum takeoff weight of 197,900 pounds.

[[Page 8148]]

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Boeing must show that the 
Model 737-10 airplane, as changed, continues 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 airplane 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of Sec.  21.16.
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same novel or 
unusual design feature, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, these special conditions would also apply to 
the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Boeing Model 737-10 airplane must comply with the fuel-
vent and exhaust-emission requirements of 14 CFR part 34, and the 
noise-certification requirements of 14 CFR part 36.
    The FAA issues special conditions, as defined in Sec.  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 airplane will incorporate the following 
novel or unusual design feature:
    Single-occupant oblique seats, with airbag devices and 3-point 
restraints, installed at 49 degrees relative to the airplane cabin bow-
to-stern centerline.

Discussion

    Section 25.785(d) requires that each occupant of a seat installed 
at an angle of more than 18 degrees, relative to bow-to-stern 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 Boeing Model 737-10 airplane single-occupant oblique seat 
installation, with airbag devices and 3-point restraints, is novel such 
that the current requirements do not adequately address airbag 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. For example, at these angles, lateral neck bending and 
other injury mechanisms prevalent from a fully side-facing installation 
become a concern. Although special conditions no. 25-552-SC was issued 
for Boeing Model 787 airplane seats installed at 49 degrees in 2014, 
that document is no longer applicable because they were issued prior to 
the current oblique-seat special conditions that are based on the July 
11, 2018, FAA policy statement PS-AIR-25-27, ``Technical Criteria for 
Approving Oblique Seats.'' These special conditions are based on the 
Boeing Model 787 airplane special conditions, with updates from that 
policy statement, and to align with the fully side-facing-seat 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 
occupants of forward- and aft-facing seats, additional airworthiness 
standards, in the form of dynamic testing requirements, including both 
the injury criteria limits from the oblique-seat policy and the fully 
side-facing-seat policy through new special conditions, are necessary.
    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. 25-21-05-
SC for the Boeing Model 737-10 airplane, which was published in the 
Federal Register on December 15, 2021 (86 FR 71183). The FAA received 
one comment from the Air Line Pilots Association, International, in 
support of the special conditions.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 737-10 airplane. Should Boeing apply at a later date for a 
change to the type certificate to include another model incorporating 
the same novel or unusual design feature, these special conditions 
would apply to that model as well.

Conclusion

    This action affects only a certain novel or unusual design feature 
on one model of airplane. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

Authority Citation

    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701, 44702, 44704.

The 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 Boeing Model 737-10 airplanes.
    In addition to the requirements of Sec. Sec.  25.562 and 25.785, 
passenger seats with airbag devices and 3-point restraints, installed 
at an angle 49 degrees relative to the airplane cabin bow-to-stern 
centerline, must meet the following:

a. Head Injury Criteria (HIC)

    HIC assessments are required only for head contact with the seat 
and other structure.
    1. Compliance with Sec.  25.562(c)(5) is required, except that, 
because an airbag device is present in addition to the 3-point 
restraint system, when the anthropomorphic test dummy (ATD) has no 
apparent contact with the seat and other structure but has contact with 
the airbag, a HIC 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. ATD head contact with the seat or other structure through the 
airbag, or contact subsequent to contact with the airbag, requires an 
HIC value not exceeding 1000.
    3. The HIC value must not exceed 1000 in any condition in which the 
airbag 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 head, must provide that support in a 
consistent manner regardless of occupant stature. Otherwise, additional 
HIC assessment tests may be needed.

[[Page 8149]]

b. Body-to-Wall/Furnishing Contact

    If a seat is installed aft of 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 may require 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 reason to also 
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 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,'' applying 
the following criteria: 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

    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 (CFC) 600 as defined in SAE Recommended 
Practice J211-1, ``Instrumentation for Impact Test Part 1--Electrionic 
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 
the 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, conducted to measure the injury 
criteria above, using the FAA Hybrid III ATD or using 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), to 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 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 the FAA Hybrid II 
ATD (49 CFR part 572, subpart B, as specified in Sec.  25.562) or 
equivalent.
    5. The design and installation of seatbelt 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

    An inflatable airbag-restraint system will be installed, and must 
meet the requirements of Special Conditions No. 25-386-SC, ``Boeing 
Model 737-600/-700/-700C/-800/-900 and 900ER Series

[[Page 8150]]

Airplanes; Seats With Inflatable Lapbelts,'' applicable to Boeing Model 
737-10 series airplanes.

i. General Test Guidelines

    1. The determination of the appropriate ATD to be used in assessing 
occupant injury (FAA Hybrid III or ES-2re) is 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, 
are required.
    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 FAA Hybrid III ATD or ES-2re ATD, undeformed floor, yaw, and with 
all lateral structural supports (e.g., armrests or walls) critically 
represented, and which are within contact range of the occupant.
    i. Pass/fail injury assessments:
    A. Perform HIC, fore and aft neck injury, spinal tension, and femur 
evaluations using the FAA Hybrid III ATD.
    B. Perform lateral neck injury, thoracic, abdominal, pelvis, and 
femur evaluations using the ES-2re ATD.
    5. For injury assessments accomplished by testing with the ES-2re 
ATD for longitudinal tests 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 such 
that they are on the side of the ATD 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 captured during the test. The ES-2re jacket is sufficient 
for torso clothing, although a form-fitting shirt may be used in 
addition, 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) to 
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 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 joints' 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.

    Note: Seats installed via plinths or pallets must meet 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.


    Issued in Kansas City, Missouri, on February 8, 2022.
Patrick R. Mullen,
Manager, Technical Innovation Policy Branch, Policy and Innovation 
Division, Aircraft Certification Service.
[FR Doc. 2022-03012 Filed 2-11-22; 8:45 am]
BILLING CODE 4910-13-P