Action
Final rule.
Summary
We are adopting a new airworthiness directive (AD) for all Eurocopter France (EC) Model SA-365N, SA-365N1, SA-366G1, AS-365N2, AS 365 N3, EC 155B, and EC155B1 helicopters. This AD was prompted by the discovery of a cracked main rotor mast nut. This condition, if not corrected, could lead to complete failure of the mast nut, resulting in failure of the rotor mast and loss of control of the helicopter. This AD will require replacing the main rotor mast nut with an airworthy main rotor mast nut to prevent this scenario.