Airworthiness Directives; Eurocopter France Model EC 120B Helicopters

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 99-19-23 which was sent previously to all known U.S. owners and operators of Eurocopter France Model EC 120B helicopters by individual letters. This AD requires, at specified time intervals, inspecting the engine coupling tube for cracks and replacing any cracked engine coupling tube with an airworthy engine coupling tube. This amendment is prompted by the discovery, during routine maintenance inspections, of three cracked engine coupling tubes caused by structural resonance. The actions specified by this AD are intended to detect a crack in the engine coupling tube which could result in coupling failure, loss of engine drive, and a subsequent forced landing.