Summary
The FAA proposes to revise an existing airworthiness directive (AD) that applies to certain Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-300, 747-400, 747-400D, and 747SR series airplanes. The existing AD currently requires repetitive inspections to detect cracking of certain lower lobe fuselage frames, and repair if necessary. This proposed AD would specify appropriate service information for certain corrective actions. This proposed AD results from reports indicating that fatigue cracks were found in lower lobe frames on the left side of the fuselage. We are proposing 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.