Summary
We propose to adopt a new airworthiness directive (AD) for all The Boeing Company Model 707 airplanes, and Model 720 and 720B series airplanes. This proposed AD was prompted by reports of scribe-line- related fatigue cracks on Model 727 airplanes, which are similar in design to Model 707 airplanes, and Model 720 and 720B series airplanes. This proposed AD would require inspections for scribe lines in the skin lap joints, external approved repairs, external features, skin butt joints, and decals, and related investigative and corrective actions if necessary. This proposed AD would also require surface finish restoration. We are proposing this AD to detect and correct scribe lines, which can develop into fatigue cracks in the skin and cause rapid decompression of the airplane.