Summary
We propose to supersede Airworthiness Directive (AD) 2010-26- 10, which applies to certain The Boeing Company Model 747-200C, -200F, -400, -400D, and -400F series airplanes. AD 2010-26-10 currently requires repetitive inspections for cracking of the lap joints, modification of certain lap joints, and certain post-repair inspections of the lap joints. Since we issued AD 2010-26-10, an evaluation by the design approval holder (DAH) has indicated that certain lap joints are subject to widespread fatigue damage (WFD). This proposed AD would add new repetitive post-modification inspections for cracking in the lap joints, and repair if necessary. We are proposing 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.