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Federal Register / Vol. 86, No. 123 / Wednesday, June 30, 2021 / Proposed Rules fuselage pressurization fatigue cycles and clamp-up stresses. Cracks in the inspection area of AD 20050518 have now been found on airplanes within the range of line numbers 1167 through 1755 inclusive. At one location, the crack was linked from the first to the second fastener row. This cracking was identified during an inspection for cracking of the web lap splice of the aft pressure bulkhead, as required by AD
20171022, Amendment 3918896 82
FR 23507, May 23, 2017 AD 201710
22. The inspections and intervals specified in AD 20171022 are not adequate to address the specific fatigue cracking occurring in the web apex area that is the subject of this NPRM.
FAAs Determination The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.
Related Service Information Under 1
CFR Part 51
The FAA reviewed Boeing Alert Service Bulletin 73753A1251, Revision 2, dated January 20, 2021. This service information specifies procedures for a general visual inspection for existing
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repairs, repetitive detailed and HFEC
inspections for cracks around the web fasteners, repetitive LFEC inspection for cracks around the hidden web lap splice fastener locations, and repair of cracks.
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.

identified as exceptions in the regulatory text of this proposed AD.
For information on the procedures and compliance times, see this service information at https
www.regulations.gov by searching for and locating Docket No. FAA2021
0503.

Proposed AD Requirements in This NPRM

For Group 1 airplanes, the Accomplishment Instructions of Boeing Alert Service Bulletin 73753A1251
Revision 2, dated January 20, 2021, do not include any RC required for compliance steps. The RC tagging was inadvertently removed from Boeing Alert Service Bulletin 73753A1251
Revision 2, dated January 20, 2021. For Group 1 airplanes, this proposed AD
would therefore require treating Step 3.B.2. of the Accomplishment Instructions of Boeing Alert Service Bulletin 73753A1251 Revision 2, dated January 20, 2021, as an RC step.

Although this proposed AD does not explicitly restate the requirements of AD
20050518, this proposed AD would retain all of the requirements of AD
20050518. Those requirements are referenced in the service information identified previously, which, in turn, is referenced in paragraph g of this proposed AD. This proposed AD would revise the applicability to include additional airplanes, and add an inspection for existing repairs on those airplanes. This proposed AD would also require accomplishment of the actions identified as RC required for compliance in the Accomplishment Instructions of Boeing Alert Service Bulletin 73753A1251, Revision 2, dated January 20, 2021, described previously, except for any differences
Differences Between This Proposed AD
and the Service Information
Costs of Compliance The FAA estimates that this AD, if adopted as proposed, would affect 744
airplanes of U.S. registry. The FAA
estimates the following costs to comply with this proposed AD:

ESTIMATED COSTS
Action
Labor cost
Detailed, HFEC, and LFEC inspections.
General visual inspection 194 airplanes.

Parts cost
Up to 10 work-hours $85 per hour = Up to $850 per inspection cycle.
1 work-hour $85 per hour = $85

The FAA estimates the following costs to do any necessary repairs that
Cost per product $0
0

Up to $850 per inspection cycle.
$85

would be required based on the results of the proposed inspections. The FAA

Cost on U.S. operators Up to $632,400 per inspection cycle.
$16,490.

has no way of determining the number of aircraft that might need these repairs:

ON-CONDITION COSTS
Action
Labor cost
Parts cost
Repair

Up to 30 work-hours $85 per hour = Up to $2,550

Up to $30,000

Cost per product Up to $32,550

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Repair costs will vary depending on size of the repair required.

Authority for This Rulemaking Title 49 of the United States Code specifies the FAAs 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 Agencys 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

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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 rulemaking action.
Regulatory Findings The FAA has determined that this proposed AD would not have federalism
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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 that the proposed regulation:
1 Is not a significant regulatory action under Executive Order 12866, 2 Would not affect intrastate aviation in Alaska, and
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