Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747SR, and 747SP Series Airplanes

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Boeing Model 747 series airplanes. That AD currently requires inspecting to detect cracking in certain lower lobe fuselage skin lap joints, doing repetitive inspections for cracking at certain fastener locations having countersunk fasteners, and replacing countersunk fasteners with protruding head fasteners at certain fastener locations. This new AD requires replacing a previous high-frequency eddy current (HFEC) inspection method with a new HFEC inspection method, adding a one-time inspection for cracking of certain airplanes, and terminating the adjustment factor for the inspection compliance times based on cabin differential pressure. This AD also requires inspecting additional lap joints. This AD results from reports of fuselage skin cracks found at certain countersunk fastener locations in the upper row of lap joints near the wing-to-body fairings, and from a report that the presence of Alodine-coated rivets could cause faulty results during the required inspections using the optional sliding probe HFEC inspection method specified in the existing AD. We are issuing this AD to prevent reduced structural integrity of the fuselage.