The pilot involved in a fatal maintenance ground run abbreviated the operator’s checklist, missing crucial steps that led the aircraft to perform a “rapid rotation” striking two maintenance engineers, an accident investigation from the Transportation Safety Board (TSB) of Canada has revealed.
The incident happened on May 6, 2023, as the aircraft — an Airbus AS350 B3 operated by Mustang Helicopters — was completing its third maintenance ground run to balance its tail rotor drive shaft at Smithers Airport in British Columbia.
After the pilot increased the aircraft engine power from IDLE to FLT (flight idle), it suddenly began to rotate to the right — but the pilot was looking down at the time. Its tail rotor struck two maintenance technicians who had been working with the pilot, fatally injuring one and causing serious injuries to the other.
In its final report on the accident, the TSB said the pilot “expressed to the maintenance staff members that he was interested in following a live sporting event using his cellphone, which he brought into the cockpit” before the first maintenance ground run. He was wearing a Bluetooth earbud in his left ear and listening to music playing through the earpiece.
When the pilot started the helicopter for the second ground run, he did so after completing, from memory, an abbreviated version of the steps in the pre-start and start sections of Mustang’s checklist — omitting the freedom of travel controls check, the hydraulic accumulator check, and the hydraulic pressure isolation check.
The helicopter was shut down using the post-landing and shutdown section of the checklist from memory, but the pilot forgot to complete the yaw load compensator check.
“The yaw load compensator check includes a step where anti-torque pedals are manually re-centred, creating an opportunity for the anti-torque pedals to be placed in the correct position for the next pre-start,” the TSB report states.
“Without completing the yaw load compensator check, the pedals will hydraulically lock with the right anti-torque pedal fully forward.”
When he started the helicopter for a third time, he used the same abbreviated version of the pre-start and start checklists, from memory, as he had before. The TSB said his feet were either lightly resting on the bottom of the anti-torque pedals, or not on them at all. Once the aircraft had reached flight idle, it lifted slightly and began to rotate.
The pilot moved the engine control to IDLE, turned off the fuel and applied the rotor brake, but the helicopter had already rotated 540 degrees by the time it stopped. The TSB said it could not determine if he had tried to counteract the rotation with the anti-torque pedals.
The aircraft manufacturer, Airbus Helicopters, recreated the incident conditions — starting and running an AS350, shutting it down without depleting the tail rotor accumulator or completing the yaw load compensator check, and then restarting it without completing the two pre-flight hydraulic checks — and the same uncommanded rotation began when engine power was increased to flight idle.
The TSB reiterated the risks of using cellphones or other portable electronic devices (PEDs) in various transportation modes. While it said it could not determine whether the pilot was interacting or viewing his cellphone immediately before the incident, it highlighted the fact that there are no regulations in Canada that prohibit the non-essential use of PEDs in the cockpit — whereas the U.S. Federal Aviation Administration prohibits the use of PEDs by flight crew members in airline operations while the aircraft is being operated.
After the incident, Mustang Helicopters introduced a new distraction policy, which includes stowing electronic devices, and changed its maintenance procedures to require that aircraft maintenance engineers to be inside the helicopter during maintenance ground runs.
