Airworthiness Directives; Boeing Model 747-100, 747SP, and 747SR Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747-100, 747SP, and 747SR series airplanes, that requires repetitive inspections to find fatigue cracking between the seal ribs of the front spar web of the wing and outboard of the outboard seal rib to front spar station inboard (FSSI) 711, and repair of cracked structure. This AD also provides for an optional modification of a certain area. This action is necessary to find and fix fatigue cracking between the seal ribs of the front spar web of the wing and outboard of the outboard seal rib to FSSI 711, 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.