Heli Downed By Turbine Blade Failure

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A Eurocopter AS3450BA that autorotated onto a canopy of trees in Maui lost power due to failure of a turbine blade, according to probable cause and factual reports released by the NTSB. All five aboard escaped serious injury, except the pilot, who broke his ankle. The NTSB reported that its investigation revealed "that the second stage turbine (T2) blade tips all exhibited fractures, and a single blade had separated at the blade platform flush with the disk circumference." Further, "a material laboratory analysis determined that the turbine blade failure was a result of a fatigue fracture that was initiated at a corrosion/oxidation pit." The engine involved was a Turbomeca Arriel 1B that had "operated for 9,593 hours since new, and 1,764 hours since the last overhaul." Turbomeca issued Service Letter No. 2436/06/ARL/182, dated April 12, 2006, notifying operators that Turbomeca was reducing the service life of the Arriel 1B second stage turbine blades from 6,000 hours to 3,000 hours. The company also issued Mandatory Service Bulletin No. A292 72 0807, and the FAA issued Airworthiness Directive 2006-02-08R1 and 2006-06-17.