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Federal Register / Vol. 86, No. 34 / Tuesday, February 23, 2021 / Rules and Regulations
Request To Clarify an Inspection Area Delta requested clarification on the inspection area addressed in certain portions Part 2, Step 3 and View 2D21s flagnote 63 of Boeing Multi Operator Message MOMMOM200049
01BR1, dated January 29, 2020. Delta stated that those parts could be interpreted to specify that the entire front spar of the center tank must be inspected for the fillet seal and SOB
slot, or only the SOB slot area.
The FAA agrees that the specifications of the area to be inspected should be clearer. As discussed above, the FAA has revised this AD to reference Boeing Multi Operator Message MOMMOM200049
01BR4, dated September 28, 2020, which clarifies that only the SOB slot area must be inspected as shown in Figure 1 of Boeing Multi Operator Message MOMMOM200049
01BR4, dated September 28, 2020. No additional changes to this AD have been made.
Request To Add Service-Based Compliance Time Southwest Airlines requested that a service-based compliance time be added to the calendar-based compliance time proposed in the NPRM. Southwest Airlines proposed that the compliance time be re-written to require compliance within 9 months or 2,000 flight cycles from AD effective date, whichever occurs later. Southwest Airlines pointed out that due to the reduced flight schedules in response to the COVID19 pandemic, many airplanes are in long-term storage. Southwest Airlines added that some of these longterm storage facilities might not be capable of providing heavy maintenance, and airplanes would need to be ferried to a facility where these actions may be accomplished.
The FAA disagrees with adding the 2,000 flight cycles to the compliance time. In developing an appropriate compliance time, the FAA considered the safety implications, parts availability, and normal maintenance schedules. In consideration of all of these factors, the FAA determined that the compliance time, as proposed, represents an appropriate interval for the general visual inspection for insufficient sealant in the SOB slot within the fleet, while still maintaining an adequate level of safety. However, under the provisions of paragraph k of this AD, the FAA will consider requests for approval of an extension of the compliance time if sufficient data are submitted to substantiate that the new compliance time would provide an
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acceptable level of safety. The FAA has not changed this AD in this regard.
Request To Extend Compliance Time Alaska requested that an additional compliance time deferral of 24 months be allowed under the following conditions: No fuel contamination in the ADMB; no external leak or signs of a previous external leak around the SOB
slot; insufficient sealing conditions temporarily corrected with PR1826 B
1/4 sealant or SF5387 secondary fuel barrier materials, in accordance with certain service information instructions;
and repetitive inspections for fuel contamination of the ADMB done at intervals not to exceed 12 months until the repair specified in paragraph g of this AD is completed. Alaska stated that the extended compliance time would relieve some of the operational impact and would aid in planning for the timeintensive repair during a heavy maintenance visit.
The FAA does not agree to provide a 24-month compliance time for the repair. The technical specifications provided for the proposed alternative sealant for temporary repair do not provide the FAA with enough information to determine that the temporary repair would comply with the certification basis of the airplane and provide an acceptable level of safety when incorporated into the existing fuel system design. There is also insufficient information on how the procedures for use in the temporary repair would differ from the permanent repair. However, under the provisions of paragraph k of this AD, the FAA will consider requests for approval of an extension of the repair compliance time if sufficient data are submitted to substantiate that the conditions and temporary repair would provide an acceptable level of safety.
The FAA has not changed this AD in this regard.
Request To Allow Removing Certain Other Parts To Gain Inspection Access American Airlines and Delta requested a revision to the proposed AD
to allow removing the air return grilles or sidewall panels to expose a hole in a beam above the SOB slot area so the inspection of the sealant can be done through the opening. Both commenters stated that the access procedure specified in Boeing Multi Operator Message MOMMOM200049
01BR1, dated January 29, 2020, removes seats and cabin floor panels to gain access to the inspection area.
American Airlines also stated that allowing the alternative access procedure for the inspection would reduce the amount of time necessary to
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accomplish an inspection of the SOB
slot, and that accomplishing any required corrective action would then require the removal of seats and cabin floor panels to gain access to the SOB
slot area.
The FAA agrees that the inspection could be accomplished by removing the air return grilles or sidewall panels. As discussed previously, the FAA has revised this AD to reference Boeing Multi Operator Message MOMMOM
20004901BR4, dated September 28, 2020, which does contain this additional method of compliance for accessing the inspection area. The FAA
has not made any additional revisions to this AD in this regard.
Request To Allow Use of Alternative Sealant Alaska stated that the sealant AC360
B1/2, which is specified as the sealant to use to fill a void, is discontinued. The FAA infers that Alaska wants the AD to be revised to remove reference to the discontinued sealant.
The FAA agrees that the sealant AC
360 B1/2 has been discontinued. As discussed above, this AD has been revised to reference Boeing Multi Operator Message MOMMOM20
004901BR4, dated September 28, 2020, which removes the reference to the sealant AC360 B1/2, but retains the reference to sealant BMS 5142, which is the appropriate sealant to use. The FAA has not made any further changes to this AD in this regard.
Request To Use Faster-Curing Sealants Alaska requested that the FAA allow alternative sealants that cure faster than the ones specified in the service information. Alaska suggested allowing the use of sealant PR1826 B1/4 in place of BMS 5142, and SF5387 in place of BMS 581. Alaska also provided technical data sheets for the proposed sealants. Alaska noted that use of the slower-curing sealants could result in an airplane being out of service for up to 34 hours, and that time could be reduced by use of faster-curing sealants that provide an equivalent level of safety.
The FAA agrees that the alternative sealants would provide a faster cure time. However, the FAA does not have enough data to determine if the alternative sealants comply with the certification basis of the airplane and if they will provide an acceptable level of safety when incorporated into the existing fuel system design. The FAA
will consider requests for alternative sealants as an alternative method of compliance if requested using the procedure specified in paragraph k of
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