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Federal Register / Vol. 86, No. 34 / Tuesday, February 23, 2021 / Rules and Regulations information. The address for Docket Operations is U.S. Department of Transportation, Docket Operations, M
30, West Building Ground Floor, Room W12140, 1200 New Jersey Avenue SE, Washington, DC 20590.
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
2313622; email: james.laubaugh@
faa.gov.
SUPPLEMENTARY INFORMATION:

Discussion The FAA issued a notice of proposed rulemaking NPRM to amend 14 CFR
part 39 by adding an AD that would apply to certain The Boeing Company Model 737600, 700, 700C, 800, 900, and 900ER series airplanes. The NPRM published in the Federal Register on May 6, 2020 85 FR 26893.
The NPRM was prompted by 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 737600, 700, 700C, 800, 900, and 900ER series airplanes. The NPRM proposed to require a general visual inspection for insufficient sealant in the SOB slot, and related investigative and corrective actions.
The FAA is issuing this AD to address fuel leaking into the air distribution mix bay ADMB, which if not addressed, could possibly lead to an ignition of flammable fluid vapors, fire, or explosion, or fuel vapor inhalation by passengers and crew.
Comments The FAA gave the public the opportunity to participate in developing this final rule. The following presents the comments received on the NPRM
and the FAAs response to each comment.
Supportive Comment United Airlines stated it had no technical objection to the NPRM.
Effects of Winglets on Accomplishment of the Proposed Actions Aviation Partners Boeing stated that the installation of blended or split scimitar winglets per Supplemental Type Certificate STC ST00830SE does not affect compliance with the proposed actions.
The FAA agrees with the commenter that STC ST00830SE does not affect the accomplishment of the manufacturers
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service instructions. Therefore, the installation of STC ST00830SE does not affect the ability to accomplish the actions required by this AD. The FAA
has not changed this AD in this regard.
Request To Reference Later Revision of Multi Operator Message MOM
Boeing requested that the FAA revise the proposed AD to reference a later revision of the MOM, specifically, Boeing Multi Operator Message MOM
MOM20004901BR2, with an anticipated publication date of July 31, 2020. Boeing stated that the revision has improved illustration and work instructions, clarifies how to distinguish between certain application flaws and more severe flaws and deterioration, and provides relief from certain corrective actions for certain secondary fuel barrier coating conditions.
The FAA agrees to reference a later revision of the service information.
However, Boeing has released additional later revisions that provide additional clarity. Boeing Multi Operator Message MOMMOM20
004901BR4, dated September 28, 2020, provides clarification on the definitions of sufficient sealant in the SOB slot, fillet seal in the SOB slot, and secondary fuel barrier. It also provides clarifications to the inspection area, and revisions were made to improve the identification of applicable figures. The changes in the revision provide relief on repairs of serviceable secondary fuel barrier coating. This later revision 4
contains no substantive change from MOMMOM20004901BR1, dated January 29, 2020. The FAA has revised paragraphs g and i of this AD to reference Boeing Multi Operator Message MOMMOM200049
01BR4, dated September 28, 2020. The FAA has also added paragraph j to this AD to provide credit for accomplishing certain earlier revisions of this service information before the effective date of this AD.
Request To Define Type of Inspection Required Delta Air Lines Delta requested clarification on what type of inspection is needed to accomplish the inspection requirements. Delta noted that in the General Notes section of the attachment to Boeing Multi Operator Message MOMMOM20004901BR2, dated August 4, 2020, the MOM provides a definition of a detailed inspection.
However, Delta noted that because detailed inspection is not used in other parts of the service information, it seems the definition of a detailed visual inspection should have been provided instead. Delta stated that this
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inconsistency could lead to an inability to comply with the instructions in the MOM.
The FAA agrees to clarify. As stated previously, the FAA has revised this AD
to reference Boeing Multi Operator Message MOMMOM200049
01BR4, dated September 28, 2020, and in this later revision, both the steps and General Notes refer to detailed inspection as well as general visual inspection. The FAA has removed paragraph g of the proposed AD as this definition is no longer needed. The FAA
has redesignated subsequent paragraphs accordingly.
Request To Clarify Figures Alaska Airlines Alaska and Delta requested that the figures within Boeing Multi Operator Message MOMMOM
20004901BR1, dated January 29, 2020, be revised to add clarity. Alaska and Delta stated that the figures lack clear reference links from the text to the figures. Delta also stated that not addressing the unclear figures could lead to incorrect accomplishment of the SOB slot inspection.
The FAA agrees that the figures are unclear and the internal reference links need to be revised. As stated previously, this AD has been revised to reference Boeing Multi Operator Message MOM
MOM20004901BR4, dated September 28, 2020, which contains improved figure references. No further changes to this AD have been made.
Request To Clarify Inspection Area and Acceptance Criteria for Sealant Alaska, Delta, and Southwest Airlines requested clarification on what is considered to be acceptable or insufficient sealant in the SOB slot.
Alaska and Delta requested that the inspection area and acceptance criteria for sealant in the SOB slot and secondary fuel barrier be clarified.
Southwest Airlines proposed a compliance table be added to the proposed AD to define acceptable sealant conditions, and Alaska supported Southwest Airlines idea.
Delta also suggested that the unclear criteria for sealant could lead to incorrect accomplishment of the SOB
slot inspection.
The FAA agrees that the criteria for acceptable sealant are unclear. As described above, the FAA has revised this AD to refer to Boeing Multi Operator Message MOMMOM20
004901BR4, dated September 28, 2020, which clarifies the area of inspection and the acceptable conditions of the sealant.

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