Overview
On 17 April 2023, at 1134 Mountain Standard Time, a Pilatus Aircraft Ltd. PC-12/47E (registration C-GMPX, serial number 1017) operated by the Royal Canadian Mounted Police departed Whitehorse/Erik Nielsen International Airport (CYXY), Yukon, on an instrument flight rules flight to Yellowknife Airport (CYZF), Northwest Territories. The pilot was the sole occupant.
Flight and Accident
Shortly after lifting off from Runway 32L, the aircraft's stall warning system activated, issuing an aural “STALL” warning and activating the stick shaker. The pilot informed the tower controller of the intention to return for landing. At 1138, while visually manoeuvring to land on Runway 32L, the aircraft impacted terrain approximately 520 feet west-southwest of the centre of the displaced threshold, in a right-wing-low attitude. Subsequently, the aircraft hit a pile of millings with its left wing, rolled onto its left side, and slid approximately 130 feet before coming to rest on an airport service road. There was no post-impact fire.
Injuries and Damage
The pilot was seriously injured and exited the aircraft through the emergency exit with assistance from aircraft rescue and firefighting personnel, who arrived within minutes. An emergency locator transmitter signal was received by the search and rescue satellite system. The aircraft was destroyed.
Probable Cause
The investigation identified five findings as causes or contributing factors: 1. During the final moments, the aircraft's right turn in excess of 45° of bank, while at low height and just above the calculated stall speed, likely resulted in an aerodynamic stall with insufficient height to recover. 2. The stainless steel belt in the left angle of attack (AOA) transmitter experienced a fatigue crack likely due to the wet-etch design process. The belt was an on-condition component, and the fatigue cracking went undetected until the belt failed at or just before takeoff, causing the AOA transmitter to transmit a false stall signal when the aircraft became airborne. 3. While aligning for landing, the pilot experienced attentional narrowing due to an intense stress reaction to a surprise event. This focused the pilot's attention outside the aircraft, unknowingly placing it in a flight regime that likely resulted in an aerodynamic stall at very low height. 4. The RCMP's training for stall warning system malfunctions on the PC-12 focused solely on inadvertent pusher activation. Thus, the pilot did not fully understand the symptoms of a false stall warning or options to mitigate risks. 5. The PC-12 pilot operating handbook provided limited guidance on the AURAL WARN INHIBIT switch during emergencies. Consequently, the pilot was unaware that this switch could be used to quickly eliminate the false aural stall warning that distracted throughout the flight.