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Federal Register / Vol. 86, No. 178 / Friday, September 17, 2021 / Rules and Regulations prompted by a report that an operator found solid rivets with missing heads at the left buttock line 25 on the sloping pressure deck web. In the NPRM, the FAA proposed to require doing a detailed inspection of the leftand rightside sloping pressure deck at certain stations for any damaged solid rivets, and applicable on-condition actions.
The FAA is issuing this AD to address damaged or missing solid rivet heads on the sloping pressure deck web, which could result in loss of sloping pressure deck panels, causing decompression and pressure loss, and loss of the hydraulic systems in the area for wheel brakes both normal and alternate and steering, and potentially leading to runway departure and adversely affecting the structural integrity of the airplane.

for the reasons provided above; the FAA
has revised this final rule accordingly.

Discussion of Final Airworthiness Directive
AA asked if the rivet problems specified in the NPRM affect any airplanes in the AA livery, particularly N-numbers nose numbers so it can keep better track on preflights.
For clarification, this AD does affect AA airplanes because its fleet includes Model 777200 and 300ER airplanes.
This AD applies to all Model 777200, 200LR, 300, 300ER, and 777F
airplanes, as specified in paragraph c of this AD. Since all Model 777
airplanes are affected, it is not necessary to identify airplanes by N-numbers. The FAA has not changed this AD in this regard.

Comments The FAA received comments from four commenters, including Boeing, American Airlines AA, FedEx, and United Airlines UAL. The following presents the comments received on the NPRM and the FAAs response to each comment.
Request To Revise the On-Condition Actions Statement Boeing requested a revision to the oncondition actions statement in the third sentence of the Related Service Information Under 1 CFR part 51
paragraph of the NPRM. Boeing stated that the repetitive detailed inspections cover two rows of fasteners common to the affected stiffener, instead of two rows of blind fasteners and solid rivets common to the affected stiffener.
Boeing commented that the blind fastener repair option is allowed only under Condition 2 of Boeing Alert Requirements Bulletin 77753A0093
RB, dated November 24, 2020, which is limited to findings of a maximum of nine damaged rivets within the same stiffener. Boeing commented that the damage rivets must be within the same fastener row, and therefore, the compliance action does not allow for blind fasteners to be installed in both fastener rows of an affected stiffener.
Boeing commented that the revised language improves clarity of the oncondition actions because it does not imply that blind fasteners can be installed in both fastener rows of an affected stiffener.
The FAA agrees to revise the oncondition actions statement in the Related Service Information Under 1
CFR part 51 paragraph of this final rule
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Request To Revise Cost of Compliance Paragraph Boeing requested a revision to the oncondition work-hours for replacing a blind fastener. Boeing stated that the blind fastener replacement does not require internal access, and therefore, the 328 work-hours can be reduced to 11 work-hours as noted in Boeing Information Notice 77753A0093 IN 01, dated January 27, 2021.
The FAA agrees to revise the oncondition work-hours for replacing a blind fastener for the reason provided above; this final rule has been revised accordingly.
Request To Clarify the Applicability
Request To Revise the Compliance Time FedEx Express FedEx agreed with the intent of the proposed AD, but found the 16-month compliance time for the initial inspection does not align with its heavy maintenance visits and requested an extension. FedEx stated that its current heavy maintenance visits would be the suitable time to accomplish the actions in the proposed AD, and that accomplishing the initial inspection in the proposed AD may require performing special maintenance visits. FedEx commented that it currently has 26 Model 777F airplanes that have accumulated more than 32,000
flight hours, and therefore, will be required to accomplish the initial inspection within the 16-month initial compliance time.
FedEx also commented that since Boeing found the missing rivet heads from a retired Model 777200 airplane, the current in-service Model 777
airplanes can operate with missing rivets without experiencing adverse structural complications since the issue was not discovered until after that airplane retired from service.

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The FAA disagrees with the commenters request to extend the initial compliance time. The FAA
cannot assume that Model 777 airplanes can operate with missing rivet heads without experiencing adverse structural complications. The FAA determined that the compliance time, as proposed, represents the maximum interval of time allowable for the affected airplanes to continue to safely operate before the initial and repetitive inspections and on-condition actions are done. If the inspection interval were based on maintenance schedules, which vary among operators, there would be no assurance that the airplane would be inspected and repaired during that maximum interval. In addition, in developing an appropriate compliance time, the FAA coordinated with the manufacturer to provide a compliance time with an acceptable level of safety.
However, under the provisions of paragraph i 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 change would provide an acceptable level of safety.
The FAA has not changed this AD in this regard.
Request To Clarify Required Service Information FedEx requested that the FAA revise note 1 to paragraph g in the proposed AD to clarify that the proposed AD
requires accomplishment of the actions only specified in Boeing Alert Requirements Bulletin 77753A0093
RB, dated November 24, 2020. FedEx stated that note 1 does not clearly distinguish the required actions from the guidance service information for accomplishing the actions in the proposed AD.
The FAA disagrees with the commenters request to change the note.
For clarification, paragraph g of this AD states the required actions for applicable airplanes, and only specifies to do all applicable actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 777
53A0093 RB, dated November 24, 2020.
The FAA clearly states that note 1 to paragraph g of this AD is guidance and Boeing Alert Service Bulletin 777
53A0093, dated November 24, 2020, is only referred to in that note. The FAA
has not changed this AD in this regard.
Request To Clarify Repair Instructions UAL indicated support for the NPRM, but requested clarification as to what to do if a Condition 4 is found in one stiffener and a Condition 3 is found in
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