Federal Register - September 17, 2021
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Source: Federal Register
51790
Federal Register / Vol. 86, No. 178 / Friday, September 17, 2021 / Rules and Regulations
another stiffener as referenced in Boeing Alert Service Bulletin 77753A0093, dated November 24, 2020. UAL stated that Condition 4 requires operators to contact Boeing and request repair instructions and to do the repair if any damaged rivet is found on both fastener rows within the same stiffener.
In addition, UAL requested the following clarifications.
When contacting Boeing, should operators provide all details of affected stiffeners regardless of the condition identified in Boeing Alert Service Bulletin 77753A0093, dated November 24, 2020? UAL commented that Boeing Alert Service Bulletin 77753A0093, dated November 24, 2020, appears to request details associated with a specific stiffener only.
Where a Condition 4 discrepancy is present, is it acceptable to continue with the repair of an adjacent Condition 3
stiffener discrepancy or is further manufacturer approval required?
UAL stated that it assumes that the conservative approach would be for the operator to provide all details of affected stiffeners to the manufacturer and then the manufacturer will provide approval to repair both Conditions 3 and 4, as referenced in Boeing Alert Service Bulletin 77753A0093, dated November 24, 2020. UAL asserted that clarification will help operators determine which information is required by the manufacturer to make a repair assessment, and it will also provide clarification as to what to do in the event of a parallel process involving both Condition 3 and Condition 4
repair.
The FAA provides the following clarification for the commenter. This AD
requires operators to use Boeing Alert Requirements Bulletin 77753A0093
RB, dated November 24, 2020, to perform the actions required in this AD.
Boeing Alert Service Bulletin 777
53A0093, dated November 24, 2020, is for guidance only. Boeing Alert Requirements Bulletin 77753A0093
RB, dated November 24, 2020, does not specify any limitations on a Condition 3 repair based on any conditions found on another stiffener. When a Condition 3 is found, the FAA finds no issues with continuing with the Condition 3 repair of replacing all solid rivets even in the event a Condition 4 is found in an adjacent stiffener. Regarding the question on the details to provide to Boeing for a repair, as specified in Note 4. of 5.A., General Information, of Boeing Alert Requirements Bulletin 77753A0093 RB, dated November 24, 2020, operators can refer to Boeing Service Letter 777SL51013, Damage Reporting and Repair Plan/Design Guidelines, which describes what information must be provided to Boeing before a structural repair can be provided. The structural repair must be approved by the FAA or the Boeing Company Organization Designation Authorization ODA as specified in paragraph h2 of this AD. The FAA
has not revised this AD in this regard.
Conclusion The FAA reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed. Except for minor editorial changes, and any
other changes described previously, this AD is adopted as proposed in the NPRM. None of the changes will increase the economic burden on any operator.
Related Service Information Under 1
CFR Part 51
The FAA reviewed Boeing Alert Requirements Bulletin 77753A0093
RB, dated November 24, 2020. This service information specifies procedures for doing a detailed inspection of the leftand right-side sloping pressure deck from station STA 1245 to STA
1287 for any damaged i.e., missing solid rivet heads, cracking or deformation of the solid rivet, or gaps between the solid rivet head and the sloping pressure deck surface solid rivets, and applicable on-condition actions. On-condition actions include repeating the detailed inspection of the left-and right-side sloping pressure deck from STA 1245 to STA 1287 for any damaged solid rivet; repetitive detailed inspections of two rows of fasteners common to the affected stiffener for any damaged solid rivet or damaged blind fastener; replacing solid rivets or blind fasteners; and repair. 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 ADDRESSES.
Costs of Compliance The FAA estimates that this AD
affects 224 airplanes of U.S. registry.
The FAA estimates the following costs to comply with this AD:
ESTIMATED COSTS
Action
Labor cost
Detailed inspections
Up to 384 work-hours $85 per hour =
Up to $32,640.
The FAA estimates the following costs to do any necessary replacements or inspections that would be required
Cost per product
Parts cost $0
Cost on U.S.
operators
Up to $32,640
based on the results of the inspection.
The agency has no way of determining
Up to $7,311,360.
the number of aircraft that might need these replacements or inspections:
ON-CONDITION COSTS
Action
Labor cost
Parts cost
Replacement solid fastener
338 work-hours $85 per hour =
$28,730.
11 work-hour $85 per hour =
$935.
326 work-hours $85 per hour =
$27,710 per inspection cycle.
Up to $3,200
Up to $31,930.
Up to $450
Up to $1,385.
$0 per inspection cycle
$27,710 per inspection cycle.
Replacement blind fastener
Repetitive inspections of fastener rows.
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