Airworthiness Directive · Amendment 39-17165 · Main rotor drive system
Eurocopter France Helicopters
This AD applies to Eurocopter France (EC) Model SA-365N, SA-365N1, SA-366G1, AS-365N2, AS 365 N3, EC 155B, and EC155B1 helicopters with a mast nut, part number (P/N) 360A31-1020-20, installed, certificated in any category.
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.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) For EC Models SA-365N, SA-365N1, AS-365N2, and AS 365 N3, prior to accumulating 1,650 hours time-in-service (TIS) or within the next 50 hours TIS, whichever occurs later, remove mast nut P/N 360A31-1020-20 and replace with an airworthy mast nut that has a P/N other than P/N 360A31-1020-20.
(2) For EC Model SA-366G1, prior to accumulating 990 hours TIS or within the next 30 hours TIS, whichever occurs later, remove mast nut P/N 360A31-1020-20 and replace with an airworthy mast nut that has a P/N other than P/N 360A31-1020-20.
(3) For EC Models EC 155B and EC155B1, prior to accumulating 660 hours TIS or within the next 50 hours TIS, whichever occurs later, remove mast nut P/N 360A31-1020-20 and replace with an airworthy mast nut that has a P/N other than P/N 360A31-1020-20.
