Airworthiness Directives; Sikorsky Aircraft Model S-76A Helicopters

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 99-11-04 which was sent previously to all known U.S. owners and operators of Sikorsky Aircraft Model S-76A helicopters by individual letters. This AD requires, before further flight, either revising the flight manual to show reduced single-engine rotorcraft performance or determining if an AC generator interlock system is installed. If an interlock system is installed, the flight manual revision is not required. This amendment is prompted by the discovery that Sikorsky Aircraft Model S-76A helicopters with Turbomeca Arriel 1S1 engines may fail to achieve the specified single- engine rotorcraft performance if an AC generator interlock system is not installed. The actions specified by this AD are intended to prevent the inability of the rotorcraft to achieve certain published one- engine-inoperative performance.