Airworthiness Directives; Boeing Model 747 Airplanes

The FAA is adopting a new airworthiness directive (AD) for all Boeing Model 747 airplanes. This AD requires inspecting for cracks in the left- and right-side Stringer 11 longeron adjacent to the horizontal stabilizer pivot bulkhead, and related investigative and corrective actions if necessary. This AD results from a report of a crack found in the right-side Stringer 11 longeron horizontal flange, adjacent to the horizontal stabilizer pivot bulkhead, during a routine maintenance inspection. We are issuing this AD to detect and correct fatigue cracking of the longeron, which can propagate and cause damage to the adjacent horizontal stabilizer pivot bulkhead. This damage could result in loss of structural integrity and consequent inability of the bulkhead to carry flight loads, which could adversely affect controllability of the airplane.