DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2020-0331; Product Identifier 2020-NM-019-AD]
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: The FAA proposes to adopt a new airworthiness directive
for certain The Boeing Company Model 737-600, -700, -700C, -800, -900,
and -900ER series airplanes. This proposed AD was prompted by a report
that the necessary sealant was not applied to the side of body (SOB) slot
as a result of a production drawing that provided unclear SOB slot sealant
application instructions. This proposed AD would require a general
visual inspection for insufficient sealant in the SOB slot, and related
investigative and corrective actions. The FAA is proposing this AD to
address the unsafe condition on these products.
DATES: The FAA must receive comments on this proposed AD by June
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 https://www.regulations.gov. Follow
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 Boeing
Commercial Airplanes, Attention: Contractual & Data Services (C&DS),
2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600;
telephone 562-797-1717; internet https://www.myboeingfleet.com. You may
view this service information at the FAA, Airworthiness Products
Section, Operational Safety Branch, 2200 South 216th St., Des Moines,
WA. For information on the availability of this material at the FAA,
call 206-231-3195. It is also available on the internet at https://www.
regulations.gov by searching for and locating Docket No. FAA-2020-
Examining the AD Docket
You may examine the AD docket on the internet at https://www.regulations.
gov by searching for and locating Docket No. FAA-2020-0331;
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, any comments received, and other information. The street
address for Docket Operations is listed above. Comments will be
available in the AD docket shortly after receipt.
FOR FURTHER INFORMATION CONTACT: James Laubaugh, Aerospace Engineer,
Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3622; email:
The FAA invites 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-2020-0331;
Product Identifier 2020-NM-019-AD" at the beginning of your comments.
The FAA specifically invites comments on the overall regulatory,
economic, environmental, and energy aspects of this NPRM. The FAA will
consider all comments received by the closing date and may amend this
NPRM because of those comments.
The FAA will post all comments, without change, to https://www.regulations
.gov, including any personal information you provide.
The FAA will also post a report summarizing each substantive verbal
contact received about this NPRM.
The FAA has received a report indicating that the necessary sealant
was not applied to the SOB slot as a result of a production drawing
providing unclear SOB slot sealant application instructions on certain
The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes. In 2019, an operator of a Model 737-800 airplane
reported a fuel smell in the cabin, and the airplane was diverted.
During post-flight inspection, insulation blankets in the air
distribution mix bay (ADMB) were found to be soaked with fuel. The ADMB
is located in the fuselage lower lobe immediately forward of the body
station (BS) 540 front spar bulkhead. An investigation of this incident
led to the finding that there was no sealant applied in the SOB slot.
For any part of a fuel tank that is inside the pressurized boundary, a
secondary fuel barrier is required. On The Boeing Company Model 737-
600, -700, -700C, -800, -900, and -900ER series airplanes, the areas
requiring secondary barrier are the wing center section upper surface
and the part of the wing center section front spar that is inside the
pressure boundary. The secondary barrier is achieved by application of
BMS 5-81 secondary fuel barrier sealant (commonly referred to as
"vapor barrier"). On the reporting airplane, sealant inside the
center fuel tank was repaired to correct the primary leak in the tank,
and the SOB slot sealant was restored. The investigation concluded that
the production drawing lacked clarity regarding the SOB slot sealant
application. The drawing was revised beginning at line number (L/N)
937, but production planning did not reflect the drawing change until
L/N 1935. The ADMB is not a flammable fluid leakage zone and therefore
does not have ignition prevention and fire detection features, and is
also immediately adjacent to the passenger compartment. Fuel leaking
into the ADMB, if not addressed, could possibly lead to an ignition of
flammable fluid vapors, fire, or explosion, or fuel vapor inhalation by
passengers and crew.
Related Service Information Under 1 CFR Part 51
The FAA reviewed Boeing Multiple Operator Message MOM-MOM-20-0049-
01B (R1), dated January 29, 2020. This service information describes
procedures for a general visual inspection for insufficient sealant in
the SOB slot. The service information also describes procedures for
related investigative actions including a general visual inspection of
the ADMB for fuel contamination, a check for external leaks of the
center fuel tank external surfaces inside the pressure boundary, and an
internal leak check of the center fuel tank to identify the leakage
path(s). The service information also describes procedures for
corrective actions including removal of all insulation blankets below
the crease beam left side to right side, clean-up of all fuel
contamination, repair of any leak, preparation of the SOB slot for
sealing, application of sealant, and repair of the secondary fuel
barrier. 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.
The FAA is proposing this AD because the FAA evaluated all the
relevant information and determined the unsafe condition described
previously is likely to exist or develop in other products of the same
Proposed AD Requirements
This proposed AD would require accomplishing the actions specified
in the service information described previously. For information on the
procedures, see this service information at https://www.regulations.gov
by searching for and locating Docket No. FAA-2020-0331.
Costs of Compliance
The FAA estimates that this proposed AD affects 731 airplanes of
U.S. registry. The FAA estimates the following costs to comply with
this proposed AD:
|Inspection for sealant
||30 work-hours x $85 per hour
The FAA estimates the following costs
to do any necessary repairs
that would be required based on the results of the proposed inspection.
The FAA has no way of determining the number of aircraft that might
need these repairs:
|Repair of sealant
||2 work-hours x $85 per hour =
|Insulation blanket replacement
||24 work-hours x $85 per hour
||6 work-hours x $85 per hour =
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.
The FAA is 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
The FAA 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) Will not affect intrastate aviation in Alaska, and
(3) 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