Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-100, 747SP, and 747SR series airplanes. This proposal would require repetitive inspections to find fatigue cracking between the seal ribs of the front spar web of the wing, and repair of cracked structure. This proposal also provides for an optional modification of a certain area. This action is necessary to find and fix such fatigue cracking, which could result in fuel leakage into the area of the inboard engines, and consequent increased risk of a fire. This action is intended to address the identified unsafe condition.