Airworthiness Directives; Sikorsky Aircraft Corporation (Type Certificate Previously Held by Schweizer Aircraft Corporation)

We are adopting a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model 269A, 269A-1, 269B, 269C, 269C-1, 269D, and TH-55A helicopters. This AD requires repetitively inspecting and lubricating the tail rotor (T/R) driveshaft splined fittings. This AD was prompted by a report that the T/R driveshaft can disconnect due to deterioration of the splined coupling. The actions are intended to detect and prevent excessive wear of the splined coupling, which could lead to failure of the T/R driveshaft and subsequent loss of control of the helicopter.