Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes equipped with General Electric Model CF6-45 or -50 series engines; or Pratt & Whitney Model JT9D-3, -7, or -70 series engines; and all 747-E4B (military) airplanes. That AD currently requires repetitive inspections to detect cracking or fracture of the steel attachment fittings of the diagonal brace to the nacelle struts; and replacement of the attachment fittings with new steel fittings, if necessary. This action would add new repetitive inspections of the fasteners of the steel attachment fittings of the diagonal brace to the inboard and outboard nacelle struts to find discrepancies; and mandate certain one-time inspections of the existing attachment fittings, installation of new fasteners, and replacement or rework of the fittings, which would terminate the repetitive inspections. This proposal is prompted by a report of fatigue cracking in a steel attachment fitting of a diagonal brace to the number 2 nacelle strut. The actions specified by the proposed AD are intended to prevent such cracking, which could result in failure of a nacelle strut diagonal brace load path and possible separation of the nacelle from the wing.