Airworthiness Directives; Schweizer Aircraft Corporation Model 269D Helicopters

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 98-26-06 which was sent previously to all known U.S. owners and operators of Schweizer Aircraft Corporation (Schweizer) Model 269D helicopters by individual letters. This AD requires removing the main rotor drive shaft (shaft) and inspecting it for cracks. If a crack is found, replacing the shaft with an airworthy shaft is required. This AD also requires periodically verifying the torque of the main rotor hub (hub) bolts. This amendment is prompted by four reports of cracking in the shaft of helicopters with a large diameter hub. Wear patterns indicate cracking was caused by loss of clamping torque on the hub and shaft assembly due to the use of grease between the hub and shaft. This condition, if not corrected, could result in failure of the shaft and subsequent loss of control of the helicopter.