AD FAA-2013-0770

We are adopting a new airworthiness directive (AD) for certain Airbus Helicopters Model EC225LP helicopters. This AD adds a new operating limitation that requires increasing the minimum density altitude flight limitation for helicopters without certain Eurocopter modifications installed. This AD is prompted by a report that flights below a certain density altitude create oscillations in the main rotor which can transfer dynamic loads to the structure, the main gearbox (MGB), and the main servo-control inputs, which could result in subsequent loss of control of the helicopter.