Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Lockheed Model L- 1011 series airplanes, that currently requires various modifications and corrective actions to prevent a potential fire hazard caused by heat damage to the flex fuel feed line from an undetected gearbox fire. In lieu of the various modifications and corrective actions, that AD also provides for an optional terminating action (i.e., installation of a vent air tube in the gear compartment and thickened gearbox housings) for another existing AD. For airplanes on which that optional terminating action has been accomplished, this action would require accomplishment of the various modifications and corrective actions. This proposal is prompted by a report indicating that, due to bearing failure, an in-flight fire occurred on an airplane on which a thickened gearbox housing was installed. The actions specified by the proposed AD are intended to detect and correct bearing failure, which could lead to a fire in the gearbox.