Airworthiness Directives; MD Helicopters Inc. Model MD-900 Helicopters

This amendment supersedes an existing emergency airworthiness directive (AD) that applies to MD Helicopters Inc. (MDHI) Model MD-900 helicopters. That emergency AD requires, within 6 hours time-in-service (TIS), or before further flight after January 31, 2000, whichever occurs first, inspecting the main rotor upper hub assembly drive plate attachment flange (flange) and determining the torque of each flange nut (nut). If a crack is found, the hub assembly must be replaced before further flight. The emergency AD also requires, within 25 hours TIS or before further flight after January 31, 2000, whichever occurs first, inspecting the hub assembly and verifying that the torque on the nuts is correct. Replacing a cracked hub assembly with an airworthy hub assembly is required before further flight. This amendment requires the same actions as the existing emergency AD but removes the January compliance dates and corrects errors in the existing emergency AD. This amendment is prompted by the discovery that there are several errors in the emergency AD. The actions specified by this AD are intended to prevent failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter.