AD NUMBER: 2017-19-26

PRODUCT: Certain Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes.

ACTION: Final Rule.

SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2008-12-04, which applied to the aircraft listed above.

AD 2008-12-04 required various repetitive inspections to detect cracks along the chem-milled steps of the fuselage skin, and to detect missing or loose fasteners in the area of a certain preventive modification or repairs; replacement of the time-limited repair with a permanent repair, if applicable; and applicable corrective actions which would end certain repetitive inspections.

This AD reduces the post-modification inspection compliance times, limits installation of the preventive modification to airplanes with fewer than 30,000 total flight cycles, and adds repetitive inspections for modified airplanes.

This AD was prompted by an evaluation by the design approval holder (DAH) that indicated that the upper skin panel at the chem-milled step above the lap joint is subject to widespread fatigue damage (WFD) if the modification was installed after 30,000 total flight cycles.

COST: The FAA estimates this AD affects 376 airplanes of U.S. registry. The cost of the inspection is estimated to be Up to $2,125 per airplane per inspection cycle. Repairs, if necessary, are estimated to cost $85 for labor, with a "minimal" cost for parts.

DATES: This AD is effective October 30, 2017

FMI: AD