What happened
During a night-time medical evacuation flight from Wollaston Lake, Saskatchewan, a Piper PA-31-325 experienced a sudden loss of performance shortly after takeoff. The aircraft, operated by Eagle Air Services, was en route to La Ronge when the pilot reported that the engines appeared to lose synchronization immediately after activating the combustion heaters.
As the aircraft climbed, it maintained a shallow angle and eventually began a left turn. The aircraft descended and struck the ice-covered surface of Wollable Lake approximately 0.75 nautical miles from the departure runway. The impact resulted in two serious injuries—sustained by the pilot and the patient—and two minor injuries to the remaining occupants. The aircraft was destroyed in the crash.
The investigation
Investigators examined the wreckage and found that the left wing and engine had been severed from the fuselage due to impact forces. Both propellers detached from their engines during the accident. A detailed examination of the left propeller revealed that the start lock stop pins were broken, suggesting the propeller was likely in its start lock position during flight.
Testing of the right engine showed no pre-existing mechanical faults that would have caused a loss of power. However, the investigation focused on the left propeller, determining that because the blades were at the start lock position, the propeller was able to overspeed as airspeed increased. This overspeeding likely reduced effective thrust.
Furthermore, the investigation looked into the medical evacuation setup, noting that the patient was being transported using a stretcher and straps that did not meet approved installation standards. The investigation also reviewed the pilot's training and the operator's regulatory compliance regarding air ambulance procedures.
Findings
- The left propeller was likely on its start locks, which allowed the propeller to overspeed as the aircraft's airspeed increased.
- The pilot was unable to rectify the engine/propeller situation before the aircraft struck the lake.
- The severity of the patient's injuries was increased by the inadequate restraint provided by the stretcher and its straps.
- There was a lack of established standards regarding the use of stretchers and the specific operational procedures for MEDEVAC flights.