Action
Final rule.
Summary
We are superseding Airworthiness Directive (AD) 2013-24-12 for all The Boeing Company Model 747-8 and 747-8F airplanes. AD 2013-24-12 required repetitive ultrasonic or dye penetrant inspections for cracking of the barrel nuts and bolts on each forward engine mount, and related investigative and corrective actions if necessary. This new AD retains the requirements of AD 2013-24-12 and also requires installing new barrel nuts at the forward engine mounts; or identifying the part number of the barrel nuts, inspecting affected barrel nuts for gaps of the strut bulkhead and forward engine mount, and doing related investigative and corrective actions if necessary. This new AD also removes airplanes from the applicability. This new AD also requires revising the maintenance or inspection program, as applicable, to include a new structurally significant item. This AD was prompted by our determination that it is necessary to mandate the installation of new barrel nuts or new inspections to adequately address the unsafe condition. We are issuing this AD to detect and correct cracked barrel nuts on a forward engine mount, which could result in reduced load capacity of the forward engine mount, separation of an engine under power from the airplane, and consequent loss of control of the airplane.