Fire whirl, ground impact led to fatal May 2015 accident near Cold Lake: TSB
In its investigation report (A15W0069) released Thursday, the Transportation Safety Board of Canada (TSB) found that during firefighting operations, the aircraft encountered a fire whirl, which led to a loss of control and impact with terrain. The pilot was fatally injured in the accident, which occurred near Cold Lake, Alberta, on May 22. 2015.
The Conair Air Tractor AT-802A Fire Boss was operating as Tanker 692 in support of wildfire management operations 25 nautical miles northwest of Cold Lake. It was the last in a formation of four Fire Boss aircraft that had just completed two drops on the northern edge of the fire. The tankers were conducting their drops at a specified bombing height of approximately 150 to 200 feet above ground level (agl), and after releasing their loads, the aircraft would climb back up to the circuit height of approximately 1,000 feet agl. As Tanker 692 was coming out of its third drop, it encountered severe turbulence, which caused the aircraft to enter an undesired nose-up attitude, then roll to the left and pitch nose-down. The aircraft’s low altitude while fighting the wildfire made recovery improbable, resulting in impact with the terrain.
The investigation determined that the aircraft had encountered a tornado-like event generated by the fire, which is known as a fire whirl. A number of factors such as a large heat source, unstable atmosphere, and low winds can cause a fire whirl. When Tanker 692 completed its third drop on the fire, the pilot could not see the fire whirl and would not have anticipated it being in the flight path.
The investigation found that if fire behaviour training is not provided to personnel involved in fire-suppression activities, there is a risk of aircraft being flown into unsafe conditions. The investigation also found that not all types of restraint systems adequately protect pilots from the effects of severe turbulence, although this did not contribute to the accident.
Following the occurrence, Conair Group Inc. commissioned a fire behaviour study to look into the environmental conditions during the occurrence, and contracted a study into the accident. In addition, the company added a session to its training program focused on awareness of environmental conditions and the dangers around forest fires. It also conducted an operational review and installed five-point harnesses in its AT‑802 fleet.