DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2019-0323; Product Identifier 2019-NM-026-AD]
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: We propose to adopt a new airworthiness directive (AD)
certain The Boeing Company Model 737-800 series airplanes. This
proposed AD was prompted by reports of inadequate clearance between a
certain fuel quantity indicating system (FQIS) tank unit and a certain
reinforcement angle upon accomplishment of a certain modification. This
proposed AD would require a detailed inspection to measure the clearance
between the FQIS tank unit and a certain reinforcement angle, and repair
if necessary. We are proposing this AD to address the unsafe condition
DATES: We must receive comments on this proposed AD by June 28,
ADDRESSES: You may send comments, using the procedures found in
11.43 and 11.45, by any of the following methods:
Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the
instructions for submitting comments.
Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.
Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
For service information identified in this NPRM, contact Aviation
Partners Boeing, 2811 S 102nd Street, Suite 200, Seattle, WA 98168;
telephone 206-830-7699; internet https://www.aviationpartnersboeing.com.
You may view this service information at the FAA, Transport Standards
Branch, 2200 South 216th St., Des Moines, WA. For information on the
availability of this material at the FAA, call 206-231-3195.
Examining the AD Docket
You may examine the AD docket on the internet at http://www.regulations.
gov by searching for and locating Docket No. FAA-2019-0323;
or in person at Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this NPRM, the regulatory evaluation, any comments received, and other
information. The street address for Docket Operations (phone: 800-647-
5527) is listed above. Comments will be available in the AD docket
shortly after receipt.
FOR FURTHER INFORMATION CONTACT: Christopher Baker, Aerospace Engineer,
Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3552; email:
We invite you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under the ADDRESSES section. Include "Docket No. FAA-2019-0323;
Product Identifier 2019-NM-026-AD" at the beginning of your comments.
We specifically invite comments on the overall regulatory, economic,
environmental, and energy aspects of this NPRM. We will consider all
comments received by the closing date and may amend this NPRM because
of those comments.
We will post all comments we receive, without change, to http://www.
regulations.gov, including any personal information you provide. We
will also post a report summarizing each substantive verbal contact we
receive about this NPRM.
We have received reports of inadequate clearance between an FQIS
tank unit at rib 21 and the stringer U-14 reinforcement angle upon
accomplishment of the split scimitar winglet modification of
supplemental type certificate (STC) ST00830SE. Following alterations or
maintenance in this area, the FQIS tank unit and the stringer U-14
reinforcement angle must maintain a minimum 0.10-inch clearance, as
specified in Aviation Partners Boeing (APB) Service Bulletin AP737-57-
020, dated April 5, 2018. A Boeing design change led to interference
between the FQIS tank unit and the winglet structure upon installation
of STC ST00830SE. STC ST00830SE, combined with the Boeing FQIS bracket
configuration on certain airplanes, leads to inadequate clearance or
interference between the structure and the FQIS tank unit in the
outboard area of the wing tanks. APB notified Boeing of the
nonconformance when APB was unable to meet the clearance requirements
upon installation of the STC ST00830SE on two separate modifications.
Such inadequate clearance, if not addressed, could result in a
potential source of ignition in a fuel tank, consequent fire,
overpressure, and structural failure of the wing.
An ignition in the fuel tank could result from either of two
scenarios. In one scenario, if the lightning protection shield over the
out-of-tank FQIS wiring has a degraded or missing connection to the
structure, excessive current can be induced in the FQIS wiring during
lightning strike, resulting in high voltage between the fuel probe and
the structure. This high voltage from lightning-induced current,
combined with inadequate clearance of the probe from the structure,
could result in arcs and sparks in the fuel tank. A degraded or missing
lightning protection shield connection to the structure is identified
as a latent failure.
In the second scenario, electrical sparks could occur if there is a
hot short between power wiring and out-of-tank FQIS wiring, when
combined with surface coatings that are worn as a result of a probe
that has been in contact with the structure. A probe in contact with
the structure would likely remain latent for a significant period of
time with worn coatings before actual metal-to-metal contact was made,
at which time the FQIS indication for that tank would blank, eventually
resulting in the need for troubleshooting.
Related Service Information Under 1 CFR Part 51
We reviewed Aviation Partners Boeing Service Bulletin AP737-57-020,
dated April 5, 2018. This service information describes procedures for
a detailed inspection to measure the clearance between the FQIS tank
unit and stringer U-14 reinforcement angle at rib 21 (WSTA 617) on the
left-hand wing, and repair including trimming the stringer U-14
reinforcement angle to obtain minimum clearance. This service
information is reasonably available because the interested parties have
access to it through their normal course of business or by the means
identified in the ADDRESSES section.
We are proposing this AD because we evaluated all the relevant
information and determined the unsafe condition described previously is
likely to exist or develop in other products of the same type design.
Proposed AD Requirements
This proposed AD would require accomplishing the actions specified
in the service information described previously.
Costs of Compliance
We estimate that this proposed AD affects 16 airplanes of U.S.
registry. We estimate the following costs to comply with this proposed
||7 work-hours x $85 per hour =
We estimate the following costs to
do any necessary repair that
would be required based on the results of the proposed inspection. We
have no way of determining the number of aircraft that might need this
||4 work-hours x $85 per hour =
According to the manufacturer, some
or all of the costs of this
proposed AD may be covered under warranty, thereby reducing the cost
impact on affected individuals. We do not control warranty coverage for
affected individuals. As a result, we have included all known costs in
our cost estimate.
Authority for This Rulemaking
Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII: Aviation Programs,
describes in more detail the scope of the Agency's authority.
We are issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701: "General
requirements." Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
This proposed AD is issued in accordance with authority delegated
by the Executive Director, Aircraft Certification Service, as
authorized by FAA Order 8000.51C. In accordance with that order,
issuance of ADs is normally a function of the Compliance and
Airworthiness Division, but during this transition period, the
Executive Director has delegated the authority to issue ADs applicable
to transport category airplanes and associated appliances to the
Director of the System Oversight Division.
We determined that this proposed AD would not have federalism
implications under Executive Order 13132. This proposed AD would not
have a substantial direct effect on the States, on the relationship
between the national Government and the States, or on the distribution
of power and responsibilities among the various levels of government.
For the reasons discussed above, I certify this proposed
(1) Is not a "significant regulatory action" under Executive
(2) Is not a "significant rule" under the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979),
(3) Will not affect intrastate aviation in Alaska, and
(4) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by
The Proposed Amendment
Accordingly, under the authority delegated to me by the
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. The FAA amends Sec. 39.13 by adding the following new airworthiness