Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747SP, and 747SR Series Airplanes; Equipped With Pratt & Whitney Model JT9D-3 and -7 Series Engines

The FAA is adopting a new airworthiness directive (AD) for certain Boeing transport category airplanes listed above. This AD requires repetitive inspections for cracks of the upper surface of the aft lower spar web of the inboard and outboard struts, as applicable; and repetitive inspections for cracks of the upper surface of the intermediate web bay of the aft lower spar. This AD also requires repetitive inspections and torque checks of the bolts common to the aft lower spar chords and the fitting of the rear engine mount bulkhead for missing, loose, or fractured bolts, as applicable; and corrective action, if necessary. This AD is prompted by reports of cracking in the aft lower spar web and reports of missing and fractured bolts. We are issuing this AD to detect and correct cracking of the aft lower spar web, and to prevent missing, loose, or fractured bolts common to the aft lower spar chords and the fitting of the rear engine mount bulkhead, which could result in the loss of the aft lower spar load path and reduced structural capability of the pylon, which may result in the separation of the engine from the airplane.