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Federal Register / Vol. 86, No. 161 / Tuesday, August 24, 2021 / Proposed Rules
regarding the LOV applicable to their airplanes.
The FAA issued AD 20172302, Amendment 3919096 82 FR 52835, November 15, 2017 AD 20172302, for certain The Boeing Company Model 737200, 200C, 300, 400, and 500
series airplanes. AD 20172302 was prompted by an evaluation by the DAH
indicating that the fuselage crown skin panels are subject to WFD. AD 2017
2302 requires repetitive inspections, replacement, and applicable oncondition actions for certain fuselage crown skin panels. The agency issued AD 20172302 to address cracking in the fuselage crown skin panels. Multiple adjacent cracks in the fuselage crown skin could link up and lead to decompression or loss of structural integrity of the airplane.

Related Service Information Under 1
CFR Part 51
The FAA reviewed Boeing Alert Service Bulletin 73753A1358, Revision 1, dated February 26, 2021. This service information specifies procedures for repetitive non-destructive inspections for cracking, replacement of certain fuselage crown skin panels, and applicable on-condition actions. Oncondition actions include a general visual inspection of certain repairs for any loose or missing fasteners, a low frequency eddy current LFEC
inspection of certain repairs for cracking, 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 the ADDRESSES section.

Actions Since AD 20172302 Was Issued
Proposed AD Requirements in This NPRM
Although this proposed AD does not explicitly restate the requirements of AD
20172302, this AD would retain all of the requirements of AD 20172302.
Those requirements are referenced in the service information identified previously, which, in turn, is referenced in paragraph h of this proposed AD.
This proposed AD would revise certain airplane configurations and inspection locations, and add airplanes to the applicability. 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 73753A1358, Revision 1, dated February 26, 2021, described previously, except for any differences identified as exceptions in the regulatory text of this proposed AD.
For information on the procedures and compliance times, see this service
Since the FAA issued AD 201723
02, errors were found in Boeing Alert Service Bulletin 73753A1358, dated April 27, 2017, which is referenced in AD 20172302. These errors include airplanes that are incorrectly identified as being in certain groups, and inspection figures that show incorrect chem-mill locations. Additional airplanes were also identified as being subject to the unsafe condition. These errors affect operators ability to comply with AD 20172302, and the FAA
determined that a supersedure was needed to require corrected service information.
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.

information at https
www.regulations.gov by searching for and locating Docket No. FAA2021
0665.
Explanation of Proposed Compliance Time The compliance time for the replacement specified in this proposed AD for addressing WFD was established to ensure that discrepant structure is replaced before WFD develops in airplanes. Standard inspection techniques cannot be relied on to detect WFD before it becomes a hazard to flight. The FAA will not grant any extensions of the compliance time to complete any AD-mandated service bulletin related to WFD without extensive new data that would substantiate and clearly warrant such an extension.
Explanation of Proposed Applicability Model 737 airplanes having line numbers 1 through 291 have an LOV of 34,000 total flight cycles, and the actions proposed in this NPRM, as specified in Boeing Alert Service Bulletin 73753A1358, Revision 1, dated February 26, 2021, would be required at a compliance time occurring after that LOV. Although operation of an airplane beyond its LOV is prohibited by 14 CFR 121.1115 and 129.115, this NPRM would include those airplanes in the applicability so that these airplanes are tracked in the event the LOV is extended in the future.
Costs of Compliance The FAA estimates that this AD, if adopted as proposed, would affect 143
airplanes of U.S. registry. The FAA
estimates the following costs to comply with this proposed AD:

ESTIMATED COSTS
Action
Labor cost
Inspection

Up to 507 work-hours $85 per hour = Up to $43,095 per inspection cycle.
304 work-hours $85 per hour = $25,840 per skin panel.

lotter on DSK11XQN23PROD with PROPOSALS1

Replacement

The FAA estimates the following costs to do any necessary inspections that would be required based on the
Cost per product
Parts cost $0
95,000

results of the proposed inspection. The FAA has no way of determining the
Cost on U.S. operators
Up to $43,095 per inspection cycle.
$120,840 per skin panel.

Up to $6,162,585 per inspection cycle.
$17,280,120 per skin panel.

number of aircraft that might need these inspections:

ON-CONDITION COSTS
Action
Labor cost
LFEC inspection

1 work-hours $85 per hour = $85

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Cost per product
Parts cost
24AUP1

$0

$85