Aircraft configuration and illusions caused by steep terrain contributed to 2021 collision with terrain in New Brunswick
Dartmouth, Nova Scotia, 10 August 2022 — In its investigation report (A21A0024) released today, the Transportation Safety Board of Canada (TSB) found that the aircraft configuration and illusions caused by steep terrain contributed to the 2021 collision with terrain of an aerial firefighting aircraft in New Brunswick.
On 11 August 2021, the Air Tractor AT-802 aircraft operated by Forest Protection Limited as Tanker 624 was conducting forest firefighting operations out of Miramichi Airport, New Brunswick, with 1 crew member on board. Following an aborted drop of fire retardant on a forest fire, the aircraft impacted the hillside of a heavily wooded area of northern New Brunswick. The pilot sustained minor injuries. There was no post-impact fire; however, the aircraft was destroyed.
The investigation found that during the aborted drop, the power was increased to 58% of the available power, and the flaps were retracted from 30 degrees to 20 degrees. Due to the pilot’s high workload and divided attention, these settings went unnoticed. The selected power setting, combined with the flap setting, contributed to a reduced airspeed as the aircraft entered a slow climb to avoid rising terrain. As the aircraft approached the rising terrain, the low altitude and tailwind resulted in the pilot perceiving that the airspeed was sufficient, when, in fact, it was decreasing.
The acoustic structures of the stall and over-torque alarms are similar in that they are both continuous tones and do not present variation in rhythm or tempo. As the aircraft approached the stall, the stall warning horn sounded. Because the pilot perceived the aircraft’s speed to be sufficient, the pilot identified this audio tone to be the sound that warns of an over-torque condition, and as a result, he decreased power. As a result of the decreased power, the aircraft decelerated further, stalled and entered an incipient spin at an altitude too low to permit recovery.
The report also highlights the importance of recognizing hazards, such as illusions, involved with low-flying near steep or mountainous terrain. If pilots are not trained on these hazards, there is an increased risk of collision with terrain.
After the occurrence, Forest Protection Limited revised its Fire Suppression Manual, including procedures for an aborted drop. The company also amended its training to include annual mountain flying training and more frequent fire practice missions.
See the investigation page for more information.
The TSB is an independent agency that investigates air, marine, pipeline, and rail transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
For more information, contact:
Transportation Safety Board of Canada