Airworthiness Directives; The Enstrom Helicopter Corporation Model F-28C, F-28C-2, F-28F, 280C, 280F, and 280FX Series Helicopters

Abstract

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 93-24-13 that was sent previously to all known U.S. owners and operators of The Enstrom Helicopter Corporation Model F-28C, F-28C-2, F-28F, 280C, 280F, and 280FX series helicopters by individual letters. This AD requires inspecting the trim motor, wiring, and relays (trim system) for failure, rewiring the trim system, and replacing the trim actuator circuit breaker. This amendment is prompted by three reports of trim system failures resulting in inadvertent trim motor operation due to struck relays. A stuck relay could cause the trim motor to deploy to the full trim position, resulting in high cyclic control forces that significantly reduce the controllability of the helicopter. The actions specified by this AD are intended to prevent failure of the trim motor relay that could result in full deployment of the trim system, high cyclic control forces, and loss of control of the helicopter.