Helicopters Magazine

Features Procedures Safety & Training
Corrosion led to mechanical malfunction

January 10, 2013  By Carey Fredericks

Jan. 10, 2013, Gatineau, Que. - The Transportation Safety Board of Canada (TSB) today released its investigation report (A11C0152) into the September 2011 accident during a training flight in a Bell 206B helicopter operated by Wisk-Air
Limited, in Thunder Bay, Ont.

The instructor and student were practising an emergency landing exercise using a technique called autorotation.

On the afternoon of 13 September 2011, the helicopter was on a local training flight at the Thunder Bay International Airport with an instructor and a student on board. They were using the threshold of Runway 30 as a designated landing area. The student pilot entered a practice autorotation, which involved reducing the engine power setting, with intention to subsequently re-apply power when the autorotation exercise was completed. When the student pilot tried to re-apply power, the helicopter's transmission clutch did not engage, and the rotor speed decreased. The instructor took control and landed the helicopter. After the helicopter landed, the helicopter's clutch re-engaged and the main rotor mast severed just below the rotor head. The helicopter was then shut down and the crew exited without injuries. There was no fire.

The investigation found that moisture had contaminated the transmission oil causing corrosion of the internal components of the transmission-oil cooler and the clutch. Corrosion products from the oil cooler caused a blockage resulting in reduced oil flow to the clutch. The subsequent damage and overheating prevented the clutch from functioning properly.



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