Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747- 200, -300, -400 series airplanes, that currently requires repetitive high frequency eddy current (HFEC) inspections to detect cracking of the front spar web of the center section of the wing, and repair, if necessary. This action would require that the existing inspection be accomplished at a reduced threshold. This action also would add a requirement that the existing HFEC inspection be accomplished on repaired areas. This proposal is prompted by reports of cracking in repaired areas of the front spar web and cracking of the front spar web on an airplane that had accumulated fewer flight cycles than the inspection threshold of the existing AD. The actions specified by the proposed AD are intended to prevent the leakage of fuel into the forward cargo bay, as a result of fatigue cracking in the front spar web, which could result in a potential fire hazard.