Wednesday, August 1, 2007
Rotorcraft Report: NTSB Blames Air Tour Crash on Engine Blade Failure
An air tour Eurocopter AS350BA crashed in Hawaii in January 2006 because a blade in its Turbomeca Arriel 1B failed in flight and destroyed the engine, U.S. accident investigators have concluded.
The pilot broke his ankle and his four passengers suffered minor injuries after the Sunshine Helicopters aircraft, registration N3607P, lost power Jan. 10, 2006. The pilot autorotated into a dense tropical forest on a steep slope near Hana on the island of Maui. The aircraft was destroyed.
According to the U.S. National Transportation Safety Board’s report, the engine had been overhauled 1,764 hr before the accident. That work included replacing the second-stage turbine blades with overhauled blades with total time of 2,986.2 hr, well below Turbomeca’s life limit at the time of 6,000 hr.
When they tore down the engine’s Module 3 (the gas-generator, high-pressure turbine section), investigators found the tips of all the second-stage blades had been fractured. One had fractured through the "fir tree" that mates it to the turbine disk and separated from the disk. Another was found to have a fir-tree fracture, too. The failed blade’s cracks had started at pitting caused by corrosion, investigators concluded.
As a result of the investigation, the NTSB said, Turbomeca reduced the life limit of the second-stage turbine blades from 6,000 to 3,000 hr, and added inspection criteria. The U.S. FAA subsequently issued airworthiness directives requiring both inspection of second-stage turbine blades and their replacement under certain circumstances as well as inspection of second-stage turbine nozzle guide vanes. Both of those directives covered Arriel 1B, 1D, and 1D1 engines.