By Chuck Taylor
The Federal Aviation Administration today issued an urgent airworthiness directive requiring immediate inspections of Boeing 747-8s to ensure bushings are installed in power control actuators that move the horizontal stabilizers.
This AD was prompted by a report of unusual noise coming from the left inboard elevator during a functional check of the ram air turbine system, and a determination that a bushing was not installed. We are issuing this AD to detect and correct non-installation of bushings. If the bushings are not present, the stiffness of the load path will be decreased, which will cause wear of adjacent parts and increased freeplay of the elevator surfaces. Freeplay that exceeds acceptable limits could result in divergent flutter for certain maneuvers, which could lead to loss of controllability of the airplane.Boeing issued a service bulletin to operators of 747-8s on Aug. 23. The FAA action today mandates inspection and, if necessary, repair before further flight. The FAA says there are eight 747-8s in service in the U.S. Typically, foreign regulators adopt FAA rules, and there are 56 747-8s in service worldwide.