[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