Airworthiness Directives; Eurocopter France (Eurocopter) Model SA-365N, SA-365N1, AS-365N2, and AS 365 N3 Helicopters

This amendment adopts a new airworthiness directive (AD) for the specified Eurocopter model helicopters. This action requires amending the Limitations section of the Rotorcraft Flight Manual (RFM) to limit the never-exceed velocity (VNE) to 150 Knots Indicated Air Speed (KIAS) and to add a 1,500 ft/minute rate of descent (R/D) limitation beyond 140 KIAS. This action also requires installing one or more placards on the cockpit instrument panel in full view of the pilot and co-pilot. This amendment is prompted by failures of the horizontal stabilizers on recently delivered Model AS 365 N3 helicopters. Tests indicate that the failures were due to a vibration phenomenon that may arise during the descent flight phases at high speed regardless of the stabilizer installed. The actions specified in this AD are intended to restrict the VNE, to prevent failure of the horizontal stabilizer, and subsequent loss of control of the helicopter.