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PROPOSED AD THE BOEING COMPANY: Docket No. FAA-2019-0323; Product Identifier 2019-NM-026-AD.
(a) COMMENTS DUE DATE

    We must receive comments by June 28, 2019.

(b) AFFECTED ADS

    None.

(c) APPLICABILITY

    This AD applies to The Boeing Company Model 737-800 series  airplanes,
    certificated  in  any  category,   line  numbers  4919  through   5063
    inclusive, modified by supplemental type certificate (STC) ST00830SE.

(d) SUBJECT

    Air Transport Association (ATA) of America Code 28, Fuel.

(e) UNSAFE CONDITION

    This 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.  We
    are issuing this AD to address this condition, which could result in a
    potential  source of  ignition in  a  fuel  tank and  consequent fire,
    overpressure, and structural failure of the wing and possible loss  of
    the airplane.

(f) COMPLIANCE

    Comply  with this  AD within  the compliance  times specified,  unless
    already done.

(g) INSPECTION AND REPAIR

    Within  18  months  after the  effective date  of this  AD: Perform  a
    detailed inspection to determine  the clearance between the  FQIS tank
    unit at  rib 21  (WSTA 617)  and stringer  U-14 reinforcement angle in
    accordance with the  Accomplishment Instructions of  Aviation Partners
    Boeing  Service Bulletin  AP737-57-020, dated  April 5, 2018.  If  the
    measured  clearance is  less than  0.10-inch:  Before  further flight,
    perform  the  repair  action  in  accordance  with  the Accomplishment
    Instructions  of Aviation  Partners Boeing  Service Bulletin  AP737-57
    -020, dated April 5, 2018.

(h) ALTERNATIVE METHODS OF COMPLIANCE (AMOCS)

(1) The  Manager,  Seattle ACO Branch,  FAA,  has the authority to approve
    AMOCs for this AD, if requested  using the procedures found in 14  CFR
    39.19. In  accordance with  14 CFR  39.19, send  your request  to your
    principal  inspector  or  local Flight  Standards District  Office, as
    appropriate. If  sending information  directly to  the manager  of the
    certification  office,  send  it  to  the  attention  of  the   person
    identified in paragraph (i)(1) of this AD.  Information may be emailed
    to: 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.

(2) Before using any approved AMOC,  notify your appropriate principal in-
    spector, or lacking  a principal inspector,  the manager of  the local
    flight standards district office/certificate holding district office.

(3) An AMOC that provides an acceptable level of  safety  may  be used for
    any repair, modification, or alteration  required by this AD if  it is
    approved by the  Boeing Commercial Airplanes  Organization Designation
    Authorization (ODA) that has  been authorized by the  Manager, Seattle
    ACO Branch, FAA,  to make those  findings. To be  approved, the repair
    method, modification deviation, or alteration deviation must meet  the
    certification  basis   of  the   airplane,  and   the  approval   must
    specifically refer to this AD.

(i) RELATED INFORMATION

(1) For more information about this AD,  contact Christopher Baker,  Aero-
    space Engineer, Propulsion Section, FAA Seattle ACO Branch, 2200 South
    216th St., Des Moines, WA 98198;  phone and fax: 206-231-3552;  email:
    christopher.r.baker@faa.gov.

(2) For  service  information  identified  in  this  AD,  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.

Issued in Des Moines, Washington, on May 3, 2019. Michael Kaszycki, Acting
Director, System Oversight Division, Aircraft Certification Service.

DATES: We must receive comments on this proposed AD by June 28, 2019.
PREAMBLE 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2019-0323; Product Identifier 2019-NM-026-AD]
RIN 2120-AA64

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) for
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 on
these products.

DATES: We must receive comments on this proposed AD by June 28, 2019.

ADDRESSES: You may send comments, using the procedures found in 14 CFR
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.

Fax: 202-493-2251.

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:
christopher.r.baker@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

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.

Discussion

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 a
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.

FAA's Determination

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
AD:

Estimated Costs

Action
Labor cost
Parts cost
Cost per product
Cost on U.S. operators
Detailed Inspection 7 work-hours x $85 per hour = $595
$0
$595
$9,520

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
repair:

On-Condition Costs

Action
Labor cost
Parts cost
Cost per product
Repair 4 work-hours x $85 per hour = $340
$0
$340

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
rulemaking action.

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.

Regulatory Findings

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
regulation:

(1) Is not a "significant regulatory action" under Executive
Order 12866,

(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
reference, Safety.

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
directive (AD):