Action
Notice of proposed rulemaking (NPRM).
Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP series airplanes. The existing AD currently requires repetitive inspections to detect cracks and fractures of the strut front spar chord assembly (including the forward side) at each strut location, and repair if necessary. This proposed AD would add a one-time inspection for cracking of the forward side of the front spar chord assembly on the inboard and outboard struts, installation of a cap skin doublers for certain airplanes, and repair if necessary. These actions would terminate the repetitive inspections of the forward side of the strut front spar chord assembly; the inspections of the aft side assembly continue as specified in the existing AD. This proposed AD results from a report of a fractured front spar assembly for strut No. 3, which resulted in the loss of the strut upper link load path. We are proposing this AD to detect and correct cracks and fractures of the nacelle strut front spar chord assembly. Fracture of the front spar chord assembly could lead to loss of the strut upper link load path and consequent fracture of the diagonal brace, which could result in in- flight separation of the strut and engine from the airplane.