Airworthiness Directives; Boeing Model 747-100, 747-200, 747-300, 747SP, and 747SR Series Airplanes Powered by Pratt & Whitney JT9D-3 and JT9D-7 Series Engines

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747-100, 747-200, 747-300, 747SP, and 747SR series airplanes powered by Pratt & Whitney JT9D-3 or JT9D-7 series engines. That AD currently requires inspections of the vertical chords of the aft torque bulkhead of the outboard nacelle struts, corrective action, if necessary, and a modification of the vertical chords, which ends the inspections. This amendment will reduce the compliance time and repetitive intervals for the currently required inspections. These actions are necessary to prevent cracking of the vertical chords adjacent to the lower spar fitting, which could result in separation of the diagonal brace load path. Continued operation with a separated diagonal brace load path increases loads on the upper link, midspar fitting, and dual side links, which could result in separation of the strut and engine from the airplane. These actions are intended to address the identified unsafe condition.