The Transportation Safety Board has determined that a Conair Air Tractor Fire Boss air tanker was caught up in a “fire whirl” before it went down near Cold Lake, Alberta, in 2015.
The TSB said the invisible and unpredictable phenomeon caused the aircraft to pitch up and stall while it was making a drop in Alberta.
“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 board found. “The aircraft’s low altitude while fighting the wildfire made recovery improbable, resulting in impact with the terrain.”
The aircraft was one of four fighting the fire on the Cold Lake Air Weapons Range and the pilot, William Hilts, was killed.
Instrumentation on the aircraft recorded the effects of the turbulence as changing from a positive 4.2 Gs to -3.2 Gs in about a second.
Since the accident, Conair has given its pilots extra training on fire behaviour and installed five-point harnesses in the Air Tractors. The TSB said Hilts likely didn’t know what hit him.
“The pilot could not see the fire whirl, as it had not yet ingested enough loose debris to make it visible,” the report said. “Because the pilot had not experienced any difficulties on the previous drops, he likely would not have anticipated what was in the flight path.”