[Federal Register Volume 85, Number 133 (Friday, July 10, 2020)]
[Rules and Regulations]
[Pages 41331-41334]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-13759]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2019-0840; Special Conditions No. 25-769-SC]


Special Conditions: The Boeing Company Model 777-300ER Series 
Airplanes; Dynamic Test Requirements for Single-Occupant Oblique Seats 
With Pretensioner Restraint Systems

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

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for The Boeing Company 
(Boeing) Model 777-300ER series 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 single-occupant, oblique 
seats equipped with pretensioner restraint systems. 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 August 10, 2020.

FOR FURTHER INFORMATION CONTACT: Shannon Lennon, Airframe and Cabin 
Safety Section, AIR-675, Transport Standards Branch, Policy and 
Innovation Division, Aircraft Certification Service, Federal Aviation 
Administration, 2200 South 216th Street, Des Moines, Washington 98198; 
telephone and fax 206-231-3209; email [email protected].

SUPPLEMENTARY INFORMATION:

[[Page 41332]]

Background

    On July 18, 2018, Boeing applied for a change to Type Certificate 
No. T00001SE for single-occupant oblique seats with pretensioner 
restraint systems, instead of airbags, which are the typical restraints 
used to protect the passengers from head injuries. These seats are to 
be installed in Boeing Model 777-300ER series airplanes. The Boeing 
Model 777-300ER series airplanes are twin-engine, transport-category 
airplanes with passenger seating capacity of 550 and a maximum takeoff 
weight of 775,000 pounds.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 777-300ER series 
airplanes, as changed, continue to meet the applicable provisions of 
the regulations listed in Type Certificate No. T00001SE 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 Boeing Model 777-300ER series 
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, Boeing Model 777-300ER series airplanes 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 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 777-300ER series airplanes will incorporate the 
following novel or unusual design feature:
    Single-occupant oblique seats with pretensioner restraint systems 
to protect the passengers from head injuries.

Discussion

    Boeing will install, in Model 777-300ER series airplanes, oblique 
(side-facing) seats that incorporate seatbelts with a pretensioner 
system at each seat place, to comply with the occupant injury criteria 
of Sec.  25.562(c)(5).
    The FAA has been conducting and sponsoring research on appropriate 
injury criteria for oblique seat installations. However, the FAA 
research program is not complete, and the FAA may update these criteria 
as further research results are collected. To reflect current research 
findings, the FAA issued policy statements PS-ANM-25-03-R1, ``Technical 
Criteria for Approving Side-Facing Seats,'' November 12, 2012, which 
updates injury criteria for fully side-facing seats, and PS-AIR-25-27, 
``Technical Criteria for Approving Oblique Seats,'' July 11, 2018, to 
define injury criteria for oblique seats. These policies provide 
background and technical information as well as applicable injury 
criteria.
    The installation of obliquely oriented passenger seats are novel 
such that the current certification basis does not adequately address 
occupant-protection expectations with regard to the occupant's neck and 
spine for seat configurations that are positioned at an angle greater 
than 18 degrees from the airplane longitudinal centerline.
    The installation of passenger seats at angles between 18 and 45 
degrees from the airplane longitudinal centerline are unusual due to 
the seat occupant interface with the surrounding furniture, and which 
introduce occupant alignment and loading concerns with or without the 
installation of 3-point or airbag-restraint systems.
    FAA-sponsored research has found that an unrestrained 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 the FAA Hybrid III anthropomorphic 
test device (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 spinal-tension 
limit selected is conservative with respect to other aviation injury 
criteria because it corresponds to a no-injury loading condition, but 
the degree of conservatism is unknown because the precise spinal-
loading level at which injuries would begin to occur is unknown. The 
small number of human-subject tests accomplished during this research 
project limits the robustness of the selected tension limit.
    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 exist that 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. This 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. 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 777-300ER series 
airplane oblique seat installations do not address oblique seats with 
3-point restraint systems equipped with

[[Page 41333]]

pretensioners. Therefore, the proposed configuration requires special 
conditions.
    Conditions 1 through 6 address occupant protection in consideration 
of the oblique-facing seats. Conditions 7 through 10 ensure that the 
pretensioner system activates when intended, to provide the necessary 
protection of occupants. This includes protection of 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.
    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. 25-20-01-
SC for the Boeing Model 777-300ER series airplane, which was published 
in the Federal Register on March 2, 2020 (85 FR 12227). The FAA 
received responses from one commenter.
    Boeing suggested one edit for clarity, to the paragraph immediately 
preceding the list of conditions in the Special Conditions section, to 
change text that reads, ``. . . passenger seats installed at an angle 
18 degrees and 45 degrees . . .'' to read, ``. . . passenger seats 
installed at an angle between 18 degrees and 45 degrees . . .'' The FAA 
concurs with the suggested change because the change more correctly 
conveys the installation angle range for oblique seats discussed in 
these special conditions.
    Boeing recommended adding two sentences at the end of condition no. 
7, regarding HIC, to be consistent with same-topic special conditions 
previously issued. It is the FAA's understanding that the proposed 
pretensioner restraint system is intended to replace the use of an 
airbag system as mentioned in the Background section of this document. 
Therefore, the information Boeing requested, pertaining to HIC 
associated with airbag contact, would not apply to these special 
conditions as originally proposed. However, in the event that an airbag 
device is incorporated in conjunction with a pretensioner restraint 
system, the FAA agrees to include the additional information consistent 
with the information provided in recently published oblique-seat 
special conditions. When present, the airbag device (e.g., inflatable 
lap-belt airbag or structure-mounted airbag) must also meet the 
existing special conditions applicable to either inflatable lap belts 
or structure-mounted airbags.
    Except as discussed above, the special conditions are adopted as 
proposed.

Applicability

    As discussed above, these special conditions are applicable to 
Boeing Model 777-300ER series airplanes. 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 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, 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 777-300ER 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 
airplane longitudinal centerline must meet the following:
    1. Body-to-Wall and Body-to-Furnishing Contact:
    If a seat is installed aft of structure, such as an interior wall 
or furnishings, and which 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 which 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:
    a. 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.
    b. 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 for tension
    Fzc = 1,385 lbs for compression
    Myc = 229 lb-ft in flexion
    Myc = 100 lb-ft in extension

    c. Peak Fz must be below 937 lbs in tension and 899 lbs 
in compression.
    d. Rotation of the head about its vertical axis relative to the 
torso is limited to 105 degrees in either direction from forward 
facing.
    e. 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 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. 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.

[[Page 41334]]

    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.
    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.
    When an airbag device is present in addition to the pretensioner 
restraint system, and the anthropormorphic test device (ATD) has no 
apparent contact with the seat/structure but has contact with an 
airbag, a HIC unlimited scored 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. 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 seating 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 Des Moines, Washington, on June 22, 2020.
James E. Wilborn,
Acting Manager, Transport Standards Branch, Policy and Innovation 
Division, Aircraft Certification Service.
[FR Doc. 2020-13759 Filed 7-9-20; 8:45 am]
BILLING CODE 4910-13-P