AD FAA-2015-3630

We are adopting a new airworthiness directive (AD) for all The Boeing Company Model 747-400F series airplanes. This AD was prompted by an analysis of the production methods used to increase fatigue resistance of the upper closure fittings at the nose cargo door portal's C-3 frame, which showed that cracking could start too early to be caught in a timely manner by the inspection or maintenance program. This AD requires inspections of the upper closure fitting and connected strap and doubler at the nose cargo door portal for cracking, and related investigative and corrective actions if necessary. We are issuing this AD to detect and correct such cracking, which could result in sudden decompression and loss of the airplane's structural integrity.