Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 707 and 720 series airplanes. This proposal would require a preventive modification of the front spar fitting on the outboard engine nacelle. This action is necessary to prevent fatigue cracking of the front spar fitting on the outboard engine nacelle, which could reduce the structural integrity of the nacelle, and result in separation of the engine from the airplane. This action is intended to address the identified unsafe condition.