Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Model 747-200C, -200F, -400, - 400D, and -400F series airplanes. The existing AD currently requires repetitive inspections for cracks in the overlapping (upper) skin, upper fastener row of the lap joints of the fuselage skin in sections 41, 42, and 46; and related investigative and corrective actions, if necessary. This proposed AD would expand the inspection area in the existing AD, and add a modification of certain lap joints and certain post-repair inspections of the lap joints. Accomplishing the modification would end the repetitive inspections required by the existing AD for the length of lap joint that is modified. This proposed AD results from a structural review of affected skin lap joints for widespread fatigue damage. We are proposing this AD to prevent fatigue cracking in certain lap joints, which could result in rapid depressurization of the airplane.