Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-300, 747-400, 747-400D, and 747SR Series Airplanes

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Boeing Model 747-100 and -200 series airplanes. That AD currently requires repetitive inspections for cracking of the station 800 frame assembly, and repair if necessary. This new AD retains the repetitive inspection requirements of the existing AD, but expands the area to be inspected. This AD also reduces the initial inspection threshold, removes the adjustment of the compliance threshold and repetitive interval based on cabin differential pressure, and adds airplanes to the applicability. This AD results from several reports of cracks of the station 800 frame assembly on airplanes that had accumulated fewer total flight cycles than the initial inspection threshold in the existing AD. We are issuing this AD to detect and correct fatigue cracks that could extend and fully sever the frame, which could result in development of skin cracks that could lead to rapid depressurization of the airplane.