Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to all Boeing Model 747-200F, 747-200C, 747-400, 747-400D, and 747-400F series airplanes. The existing AD currently requires repetitive inspections for cracking of certain fuselage internal structure (i.e., Sections 42 and 46 fuselage frames, upper deck floor beams, electronic bay access door cutout, nose wheel well, and main entry doors and door cutouts), and repair if necessary. This proposed AD would require additional repetitive inspections for cracking of certain fuselage structure (i.e., Section 41 fuselage frames where they connect to upper deck floor beams, and section 41 fuselage frames between stringer (S-8 and S-12), and related investigative/corrective actions if necessary. This proposed AD would also reduce the inspection threshold and repetitive inspection intervals for certain airplanes. This proposed AD results from fatigue tests and analysis by Boeing that identified additionalareas of the fuselage where fatigue cracks can occur. We are proposing this AD to prevent the loss of structural integrity of the fuselage, which could result in rapid depressurization of the airplane.