Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-100, -200 and 747SP series airplanes. This proposal would require repetitive detailed visual and ultrasonic inspections to detect missing, damaged, or broken taperlock bolts in the diagonal brace underwing fittings; and corrective actions, if necessary. This proposal also would require eventual replacement of the aft 10 taperlock bolts with new bolts, which would constitute terminating action for the repetitive inspections. This proposal is prompted by reports of damaged, broken, and corroded taperlock bolts of the diagonal brace underwing fittings on the outboard strut due to stress corrosion cracking. The actions specified by the proposed AD are intended to prevent loss of the underwing fitting load path due to missing, damaged, or broken taperlock bolts, which could result in separation of the engine and strut from the airplane.