[Federal Register Volume 88, Number 205 (Wednesday, October 25, 2023)]
[Rules and Regulations]
[Pages 73219-73221]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-23519]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2022-1740; Special Conditions No. 25-841-SC]


Special Conditions: The Boeing Company Model 777 Series 
Airplanes; Passenger Seats With 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 Boeing Company 
(Boeing) Model 777 series airplanes. These airplanes 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 pretensioner restraint systems 
installed on passenger seats. 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 November 24, 2023.

FOR FURTHER INFORMATION CONTACT: Shannon Lennon, Cabin Safety, 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-
3209; email [email protected].

SUPPLEMENTARY INFORMATION:

Background

    On September 30, 2021, Boeing applied for an amendment to Type 
Certificate No. T00001SE for Boeing Model 777 series airplanes. These 
airplanes, currently approved under Type Certificate No. T00001SE, are 
twin-engine, transport-category airplanes with maximum seating for 495 
passengers and a maximum takeoff weight of 775,000 pounds.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Boeing must show that Model 
777 series airplanes 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 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 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

    Boeing Model 777 series airplanes will incorporate the following 
novel or unusual design feature:
    Forward-facing seats incorporating a shoulder harness with 
pretensioner

[[Page 73220]]

device, otherwise known as a pretensioner restraint system, which is 
intended to protect the occupants from head injuries.

Discussion

    Boeing will install, in Model 777 series airplanes, forward-facing 
seats that incorporate a shoulder harness with a pretensioner system, 
for head-injury protection, at each seat place.
    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.
    The pretensioner restraint system utilizes a retractor that 
eliminates slack in the shoulder harness and pulls the occupant back 
into the seat prior to impact. This has the effect of reducing forward 
translation of the occupant, reducing head arc, and reducing loads in 
the shoulder harness.
    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 1 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.
    Conditions 1 through 4 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 5 through 10 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. 25-23-01-
SC for Boeing Model 777 airplanes, which was published in the Federal 
Register on May 11, 2023 (88 FR 30262).
    The FAA received one response, from the Air Line Pilots 
Association, International, in support of the special conditions. The 
special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to 
Boeing Model 777 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

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 Boeing Model 777 series airplanes.
    In addition to the requirements of Sec.  25.562, forward-facing 
passenger seats with pretensioner restraint systems must meet the 
following:

(1) 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 anthropomorphic test device (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.
    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.

(2) 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.

(3) 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.

(4) Occupants Adopting the Brace Position

    Occupants in the traditional brace position when the pretensioner 
activates must not experience adverse effects from the pretensioner 
activation.

[[Page 73221]]

(5) 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 to be susceptible to inadvertent 
pretensioner actuation as a result of wear and tear, nor 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 actuation 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).

(6) 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.

(7) 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.

(8) Contamination Protection

    The pretensioner mechanisms and controls must be protected from 
external contamination associated with that which could occur on or 
around passenger seating.

(9) Prevention of Hazards

    The pretensioner system must not induce a hazard to passengers in 
case of fire, nor create a fire hazard, if activated.

(10) 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 October 19, 2023.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2023-23519 Filed 10-24-23; 8:45 am]
BILLING CODE 4910-13-P