What happened
Approximately 20 minutes after departing Abbotsford airport, a Robinson R2-B helicopter, registration C-FHRL, experienced a catastrophic loss of rotor RPM while operating with a flight instructor and a student. Witnesses observed the aircraft descending in a flat attitude with pieces of the airframe falling away. The main rotor blades were observed to be stationary and coned during the descent. The aircraft struck the ground near Abbotsford, resulting in two fatalities. No fire occurred at the scene, though a strong smell of fuel was noted by responders.
The investigation
Investigators examined the wreckage and the Lycoming engine to determine the sequence of events. The debris field indicated the helicopter was moving very slowly or was nearly stationary at the time of impact. Analysis of the main rotor blades showed they had struck the fuselage, specifically the strobe light mount, which severed the tail boom. The blades were found in a 'tulip' shape, a condition consistent with low rotor-RPM.
While the engine was found to be mechanically capable of producing power prior to the crash, the carburettor heat control was found in the OFF position. At the time of the accident, weather conditions were at the threshold where carburettor icing could occur. Investigators also analyzed the electronic fuel control governor; while its operational status at the moment of the decay was unconfirmed, laboratory analysis suggested the governor was off at the time of impact.
Findings
- The primary cause of the accident was a decay in rotor RPM, which led to a rotor stall and subsequent structural failure of the tail boom.
- The specific event that triggered the RPM decay could not be definitively determined, though two scenarios were considered: a power-off descent demonstration gone wrong, or an abrupt control input by the student pilot.
- The carburettor heat being left in the OFF position increased the risk of engine performance degradation due to icing.
- The low-inertia rotor design of the Robinson R22B makes it highly susceptible to rapid RPM loss if flight controls are mishandled.