Airworthiness Directives; Enstrom Helicopter Corporation Model F-28, F-28A, F-28C, F-28C-2, F-28C-2R, F-28F, F-28F-R, 280, 280C, 280F, 280FX, TH-28, 480, and 480B Helicopters

This amendment adopts a new airworthiness directive (AD) for Enstrom Helicopter Corporation (Enstrom) Model F-28, F-28A, F-28C, F- 28C-2, F-28C-2R, F-28F, F-28F-R, 280, 280C, 280F, 280FX, TH-28, 480, and 480B helicopters. This action requires a visual check to determine if a certain serial-numbered main rotor blade retention pin (retention pin) is installed, and removing and replacing any affected retention pin with an airworthy retention pin. This amendment is prompted by a report from the manufacturer that some retention pins were not manufactured in accordance with specifications cited on the engineering drawing. The actions specified in this AD are intended to prevent failure of a retention pin, separation of a main rotor blade from the helicopter, and subsequent loss of control of the helicopter.