Action
Notice of proposed rulemaking (NPRM).
Summary
We propose to supersede Airworthiness Directive (AD) 2010-03- 05, which applies to all The Boeing Company Model 747-200C and -200F series airplanes. AD 2010-03-05 currently requires, for section 41 upper deck floor beam upper chords, an inspection for cracks of certain fastener holes, and corrective action if necessary; and repetitive replacements of the upper chords, straps (or angles), and radius fillers of certain upper deck floor beams and, for any replacement that is done, inspections for cracks, and corrective actions if necessary. Since we issued AD 2010-03-05, we have determined that the upper deck floor beams are subject to widespread fatigue damage (WFD), the existing inspection program is not sufficient to maintain an acceptable level of safety, and section 42 upper deck floor beam upper chords are subject to the unsafe condition. This proposed AD would add post- replacement inspections for section 41 and reduce certain compliance times. This proposed AD would also require repetitive inspections of section 42 upper deck floor beam upper chords, repetitive replacements of the upper chords, post-replacement inspections, and corrective action if necessary. We are proposing this AD to detect and correct cracking of the upper chords and straps (or angles) of the floor beams, which could lead to failure of the floor beams and consequent loss of controllability, rapid decompression, and loss of structural integrity of the airplane.