AD FAA-2009-0351

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 2009-07-53, which was sent previously to all known U.S. owners and operators of Sikorsky Aircraft Corporation (Sikorsky) Model S-92A helicopters by individual letters. This amendment is prompted by the failure of 2 main gearbox filter bowl assembly studs (studs) that were found broken during a fatal accident investigation in Canada. Prior to the accident, the manufacturer was investigating a July 2008 incident that also involved broken studs. In both cases, the broken studs resulted in rapid loss of oil. The failures have been tied to fretting and galling of the original titanium studs; therefore, this AD requires removing all titanium studs and replacing them with steel studs. The actions specified by this AD are intended to prevent failure of a stud, which could result in rapid loss of oil, failure of the main gearbox, and subsequent loss of control of the helicopter.