Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 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, -200, and -300 series airplanes. That AD currently requires repetitive inspections to detect cracking of certain lower lobe fuselage frames, and repair if necessary. This new AD retains all the requirements of the existing AD, and adds airplanes to the applicability. This AD results from reports indicating that fatigue cracks were found in lower lobe frames on the left side of the fuselage. We are issuing this AD to detect and correct fatigue cracking of certain lower lobe fuselage frames, which could lead to fatigue cracks in the fuselage skin, and consequent rapid decompression of the airplane.