[Federal Register Volume 84, Number 211 (Thursday, October 31, 2019)]
[Rules and Regulations]
[Pages 58311-58313]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-23740]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2019-0540; Special Conditions No. 25-757-SC]


Special Conditions: The Boeing Company Model 737 Series 
Airplanes; Seats With Inertia Locking Devices

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 737 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 an inertia locking device (ILD) 
installed in 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 December 2, 2019.

FOR FURTHER INFORMATION CONTACT: Shannon Lennon, Cabin and Airframe 
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: 

Background

    On January 27, 2012, Boeing applied for Type Certificate No. A16WE 
for Model 737-8 airplanes. On September 19, 2018, Boeing applied for a 
change to Type Certificate No. A16WE for seats with inertia locking 
devices in Model 737 series airplanes. The Model 737 series airplane is 
a twin-engine, transport-category airplane with a maximum takeoff 
weight of 194,700 pounds and seating for 220 passengers.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 737 series airplanes, as 
changed, continue to meet the applicable provisions of the regulations 
listed in Type Certificate No. A16WE, or the applicable regulations in

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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 (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for Boeing Model 737 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 737 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 737 series airplanes will incorporate the following 
novel or unusual design features:
    Seats with inertia locking devices.

Discussion

    Boeing will install, in Model 737 series airplanes, Thompson Aero 
Seating Ltd. passenger seats that can be translated in the fore and aft 
direction by an electrically powered motor (actuator) that is attached 
to the seat primary structure. Under typical service-loading 
conditions, the motor internal brake is able to translate the seat and 
hold the seat in the translated position. However, under the inertial 
loads of emergency-landing loading conditions specified in 14 CFR 
25.562, the motor internal brake may not be able to maintain the seat 
in the required position. The ILD is an ``active'' device intended to 
control seat movement (i.e., a system that mechanically deploys during 
an impact event) to lock the gears of the motor assembly in place. The 
ILD mechanism is activated by the higher inertial load factors that 
could occur during an emergency landing event. Each seat place 
incorporates two ILDs, one on either side of the seat pan. Only one ILD 
is required to hold an occupied seat in position during worst-case 
dynamic loading specified in Sec.  25.562.
    The ILD will self-activate only in the event of a predetermined 
airplane loading condition such as that occurring during crash or 
emergency landing, and will prevent excessive seat forward translation. 
A minimum level of protection must be provided if the seat-locking 
device does not deploy.
    The normal means of satisfying the structural and occupant 
protection requirements of Sec.  25.562 result in a non-quantified, but 
nominally predictable, progressive structural deformation or reduction 
of injury severity for impact conditions less than the maximum 
specified by the rule. However, a seat using ILD technology may involve 
a step change in protection for impacts below and above that at which 
the ILD activates and deploys to retain the seat pan in place. This 
could result in structural deformation or occupant injury output being 
higher at an intermediate impact condition than that resulting from the 
maximum impact condition. It is acceptable for such step-change 
characteristics to exist, provided the resulting output does not exceed 
the maximum allowable criteria at any condition at which the ILD does 
or does not deploy, up to the maximum severity pulse specified by the 
requirements.
    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 ILD 
deployment 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 1.33t1 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.
    Conditions 1 through 5 address ensuring that the ILD activates when 
intended, to provide the necessary protection of occupants. This 
includes protection of a range of occupants under various accident 
conditions. Conditions 6 through 10 address maintenance and reliability 
of the ILD, 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. 25-19-11-
SC for the Boeing Model 737 series airplanes, which was published in 
the Federal Register on August 9, 2019 (84 FR 39237). The FAA received 
responses from one commenter.
    Boeing states that, as written, because t1 is an 
arbitrary point in the shock pulse, the relevance of 1.33t1 
is unclear, and believes this is a typographical error. Boeing further 
states that the 0.5g deviation below the ideal pulse for the evaluation 
and testing of less-severe pulses was proposed for airbags where the 
airbag activates a lower pulses (9g or less). The ILD activates at a 
higher pulse (14.5g), closer to the pulse specified in the 
airworthiness requirements. Boeing states that, in this case, a 2g 
deviation below this ideal pulse is more appropriate and would be 
acceptable for ensuring the pulse meets the pulse-shape requirement.
    The FAA determined that the ideal pulse discussion in the proposed 
special conditions is consistent with FAA's previous guidance on this 
issue. The FAA's intent in the Discussion section is to model the less-
severe or reduced-pulse test conditions after the ideal pulse defined 
in AC 25.562-1B, figure 3.1, where t1 is defined as the rise 
time. The recommendation to not deviate from the ideal pulse by more 
than 0.5g until 1.33t1 is intended to ensure an appropriate 
pulse shape is achieved for such reduced-pulse tests. This is not a 
typographical error and is consistent with previous policy provided for 
conducting reduced-pulse tests for seats with airbag systems. This 
recommendation remains true regardless of the activation setting for 
the feature under consideration, provided that the activation setting 
is less than the minimum pulse defined in AC 25.562-1B, figure 3.1, 
e.g., 16g for a forward test. A 2g deviation from the ideal pulse is 
discussed in appendix 1 of AC 25.562-1B, and is relevant only when 
evaluating an actual pulse to the ideal pulse under normal (non-
reduced) conditions. Because the Discussion section of this special 
conditions document is intended to convey an acceptable means for 
conducting reduced-pulse tests, and is not a regulatory requirement, 
the content of the Discussion section remains as proposed. However, the 
FAA recognizes that other means to conduct reduced-pulse tests may be 
proposed, provided

[[Page 58313]]

that the applicant can show that the test conditions are scaled 
appropriately.
    Except as discussed above, the special conditions are adopted as 
proposed.

Applicability

    As discussed above, these special conditions are applicable to 
Boeing Model 737 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 one 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 737 series airplanes.
    In addition to the requirements of Sec.  25.562, passenger seats 
incorporating an inertia locking device (ILD) must meet the following:
    1. Level of Protection Provided by ILD--It must be demonstrated by 
test that the seats and attachments, when subject to the emergency-
landing dynamic conditions specified in Sec.  25.562, and with one ILD 
not deployed, do not experience structural failure that could result 
in:
    a. Separation of the seat from the airplane floor.
    b. Separation of any part of the seat that could form a hazard to 
the seat occupant or any other airplane occupant.
    c. Failure of the occupant restraint or any other condition that 
could result in the occupant separating from the seat.
    2. Protection Provided Below and Above the ILD Actuation 
Condition--If step-change effects on occupant protection exist for 
impacts below and above that at which the ILD deploys, tests must be 
performed to demonstrate that the occupant is shown to be protected at 
any condition at which the ILD does or does not deploy, up to the 
maximum severity pulse specified by Sec.  25.562. Test conditions must 
take into account any necessary tolerances for deployment.
    3. Protection Over a Range of Crash Pulse Vectors--The ILD must be 
shown to function as intended for all test vectors specified in Sec.  
25.562.
    4. Protection During Secondary Impacts--The ILD activation setting 
must be demonstrated to maximize the probability of the protection 
being available when needed, considering a secondary impact that is 
above the severity at which the device is intended to deploy up to the 
impact loading required by Sec.  25.562.
    5. 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.
    6. Inadvertent Operation--It must be shown that any inadvertent 
operation of the ILD does not affect the performance of the device 
during a subsequent emergency landing.
    7. Installation Protection--It must be shown that the ILD 
installation is protected from contamination and interference from 
foreign objects.
    8. Reliability--The performance of the ILD must not be altered by 
the effects of wear, manufacturing tolerances, aging/drying of 
lubricants, and corrosion.
    9. Maintenance and Functional Checks--The design, installation and 
operation of the ILD must be such that it is possible to functionally 
check the device in place. Additionally, a functional-check method and 
a maintenance-check interval must be included in the seat installer's 
instructions for continued airworthiness (ICA) document.
    10. Release Function--If a means exists to release an inadvertently 
activated ILD, the release means must not introduce additional hidden 
failures that would prevent the ILD from functioning properly.

    Issued in Des Moines, Washington, on October 25, 2019.
James E. Wilborn,
Acting Manager, Transport Standards Branch, Policy and Innovation 
Division, Aircraft Certification Service.
[FR Doc. 2019-23740 Filed 10-30-19; 8:45 am]
 BILLING CODE 4910-13-P