AD FAA-2015-2460

We are superseding Airworthiness Directive (AD) 2010-26-10, which applied to certain The Boeing Company Model 747-200C, -200F, - 400, -400D, and -400F series airplanes. AD 2010-26-10 required repetitive inspections for cracking of the lap joints, modification of certain lap joints, and certain post-repair inspections of the lap joints. This new AD adds new repetitive post-modification inspections for cracking in the lap joints, and repair if necessary. This AD was prompted by an evaluation by the design approval holder (DAH) which indicated that certain lap joints are subject to widespread fatigue damage (WFD). We are issuing this AD to detect and correct fatigue cracking in certain lap joints, which could result in rapid depressurization and consequent reduced structural integrity of the airplane.