What happened
On 13 September 2011, a Bell 206B helicopter, registered C-GDPE, was conducting local training maneuvers at Thunder Bay International Airport. The flight, operated by Wisk-Air Limited, included a student pilot and an instructor. The crew was performing 180° autorotations, using the threshold of Runway 30 as a landing area.
During the sixth maneuver of the day, the student pilot attempted a planned power recovery. As the throttle was advanced to full power, the rotor RPM began to decay. The instructor took control of the aircraft to complete the autorotation. During the landing, the crew heard loud noises from the upper deck of the helicopter. Upon touchdown, the rotor blades struck the tail boom, and the mast separated just below the rotor head. The 0 fatalities and 0 injuries were reported as the crew exited the aircraft safely after a successful emergency landing.
The investigation
The investigation focused on the drivetrain and the failure of the engine to transmit power to the rotor system. Investigators examined the transmission oil system and found evidence of internal corrosion within the freewheel assembly and the transmission oil cooler fittings. This corrosion was linked to moisture that had likely entered the system via condensation during periods of aircraft inactivity.
Technical analysis revealed that a blockage in the oil-supply restrictor, caused by aluminum and magnesium corrosion products, had severely restricted oil flow. This lack of lubrication led to the overheating and damage of the freewheel assembly components. Furthermore, the investigation noted that an optional Bell technical bulletin regarding a filter to prevent such contamination had not been implemented on this aircraft.