AD 2011-26-10 Amendment 39-16900

We are adopting a new airworthiness directive (AD) for Enstrom Helicopter Corporation (Enstrom) Model F-28C, F-28C-2, F-28F, 280C, 280F, 280FX TH-28, 480, and 480B helicopters with certain trim relays to require modifying and testing the lateral and longitudinal cyclic trim actuator assemblies. This AD was prompted by four failures in the cyclic trim system on certain Enstrom model helicopters that resulted in reduced controllability of the helicopter. These actions are intended to prevent failure of the cyclic trim system and subsequent loss of control of the helicopter.