AD 97-24-17 Amendment 39-10428

This document publishes in the Federal Register an amendment adopting priority letter airworthiness directive (AD) 97-24-17, which was sent previously to all known U.S. owners and operators of Bell Helicopter Textron Canada (BHTC) Model 407 helicopters by individual letters. This AD requires inspections of components in the tail rotor drive system for scratches, cracks, fretting, corrosion, and proper torquing, lubrications of the oil cooler blower shaft hanger bearings and oil cooler hanger bearings (hanger bearings), and removal of corrosion inhibitive adhesive barrier tape (barrier tape) from the tail rotor gearbox and the tail rotor gearbox support assembly faying surfaces. This amendment is prompted by numerous reports of three problems, all of which are related to the tail rotor drive system. The actions specified by this AD are intended to: detect scratches, cracks, fretting, and corrosion in the disc pack couplings; prevent inadequate lubrication of the hanger bearings and oil cooler blower shaft; and prevent loss of mounting torque on the tail rotor gearbox. Failure of any of these components could result in loss of power to the tail rotor and subsequent loss of control of the helicopter.