Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747 airplanes. The existing AD currently requires repetitive inspections for cracking, and repair as necessary, of lower lobe body frames (sections 42 and 46) of the fuselage. The existing AD also provides for optional modification of the frames, which terminates the repetitive inspections. This proposed AD would require additional repetitive inspections for cracking of certain fuselage frames, and corrective actions if necessary. This proposed AD would also revise the AD applicability. This proposed AD results from a new report of a crack found in a body frame with a tapered side guide bracket at fuselage station 1800, located on the left side between stringers 39 and 40; the frame was severed. We are proposing this AD to detect and correct the loss of structural integrity of the fuselage, which could result in rapid depressurization of the airplane.