Airworthiness Directives; Boeing Model 747-200, -300, and -400 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747-200, -300, and -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 amendment requires that the existing inspection be accomplished at a reduced threshold, and adds a requirement that the existing HFEC inspection be accomplished on repaired areas. This amendment 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 this 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.