AD NUMBER: 2018-10-12

PRODUCT: All Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes.

ACTION: Final rule; request for comments.

SUMMARY: This AD requires repetitive high frequency eddy current (HFEC) and detailed inspections, as applicable, for cracking of certain aft vertical stiffeners; repetitive detailed inspections for cracking of time-limited repairs, as applicable; a one-time HFEC inspection for cracking of the keel beam upper chord inboard flanges; a one-time general visual inspection for cracking of a certain angle; and applicable on-condition actions.

This AD was prompted by a report of cracks in the left-side and right-side keel beam upper chords and aft vertical stiffeners.

DATES: This AD is effective June 7, 2018. Comments must be received by July 9, 2018.

COST: The FAA estimates that this AD affects 67 airplanes of U.S. registry. The estimated costs of compliance are:

• Surface HFEC and detailed inspections of aft vertical stiffeners (for Configuration 1 airplanes) - $170 per aircraft per inspection cycle.
• Detailed inspection of aft vertical stiffeners and time-limited repair (for Configuration 2 airplanes) - $170 per aircraft per inspection cycle.
• Surface HFEC inspection of the keel beam upper chord inboard flanges and a general visual inspection of the angle (for all airplanes) - $170 per aircraft per inspection cycle.

FMI: AD