Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 707 and 720 series airplanes. This proposal would require repetitive inspections of certain stringers and around certain fastener holes of the lower skin of the wings to detect fatigue cracking, and repair, if necessary. This action is necessary to detect and correct such cracking and consequent damage to adjacent structure, which could result in reduced structural integrity of the airplane. This action is intended to address the identified unsafe condition.