Airworthiness Directives; McDonnell Douglas Helicopter Systems Model MD-900 Helicopters

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 98-12-30 which was sent previously to all known U.S. owners and operators of McDonnell Douglas Helicopter Systems (MDHS) Model MD-900 helicopters by individual letters. This AD requires inspecting the main rotor upper hub assembly (hub assembly) for cracks, and if a crack is found, replacing the hub assembly. The AD also requires verifying attachment nut torque values and a repetitive inspection at intervals not to exceed 150 hours time- in-service. This amendment is prompted by the discovery of cracks in 6 main rotor upper hub assemblies. This condition, if not corrected, could result in failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter.