Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires inspections to detect fatigue cracking of the vertical beam webs and chords of the nose wheel well (NWW) and of the inner chord and web of the fuselage frames at body station (BS) 300 and BS 320, and repair, if necessary. This amendment expands the applicability of the existing AD to include additional airplanes, and adds new requirements for repetitive inspections to detect fatigue cracking of the NWW vertical beam webs and frames from BS 260 to BS 320, and follow-on actions, if necessary, which would end the currently required inspections for airplanes subject to them. This amendment also provides terminating action for the new repetitive inspections. The actions specified by this AD are intended to detect and correct fatigue cracking of the NWW vertical beam webs and frames, which could result in collapse of the NWW pressure bulkhead and subsequent rapid decompression of the airplane. This action is intended to address the identified unsafe condition.