AD FAA-2013-0638

We are adopting a new airworthiness directive (AD) for Eurocopter Model AS350B, AS350BA, AS350B1, AS350B2, AS350B3, AS350C, AS350D, and AS350D1 helicopters with a single hydraulic system and a certain hydraulic pump drive installed. This AD requires inspecting the hydraulic pump drive pulley bearing (pulley bearing) for leaks, rust, overheating, and condition. This AD is prompted by six reports of hydraulic pump drive belt failure caused by seizure of the pulley bearing. These actions are intended to prevent hydraulic pump drive belt failure, loss of hydraulic servo assistance, and subsequent loss of control of the helicopter.