Airworthiness Directives; Boeing Model 747 Series Airplanes

The FAA is superseding an existing airworthiness directive (AD) that applies to all Boeing Model 747 series airplanes. The existing AD currently requires repetitive inspections for cracking of the top and side panel webs and panel stiffeners of the nose wheel well (NWW), and corrective actions if necessary. This new AD expands the area of inspection, adds a new "secondary" inspection if certain cracking is found, and reduces the intervals for the repetitive inspections. This AD is prompted by a report of an in-flight decompression of a Model 747-100 series airplane that had accumulated 27,241 total flight cycles. We are issuing this AD to detect and correct fatigue cracks in the top and side panel webs and stiffeners of the NWW, which could compromise the structural integrity of the NWW and could lead to the rapid decompression of the airplane.