Aircraft and Crew
Conair Group Inc. operated a Convair 580 (registration C-FKFY, serial number 129) as Tanker 448. The aircraft was configured for aerial firefighting. The crew consisted of two members, both of whom were fatally injured in the accident.
Flight History
On 31 July 2010 at 2002 Pacific Daylight Time, Tanker 448 departed Kamloops, British Columbia, to fight a wildfire near Lytton. The operation involved two aircraft: a bird dog aircraft (Rockwell Turbo Commander 690) and the tanker. The bird dog crew planned and directed the fire suppression, demonstrating the bombing run and providing a verbal description to the tanker crew.
The planned run required crossing the edge of a ravine in the side of the Fraser River canyon before descending onto the fire. The standard rectangular circuit was modified to a triangular shape due to terrain. The tanker was to make eight left-hand circuits, dropping one-eighth of its retardant load each time. A single left turn of more than 90° with a bank angle up to 40° was required, followed by a descent of 900 feet into the ravine for the drop.
Accident Sequence
About 22 minutes after departure, Tanker 448 approached the ravine and struck trees. An unanticipated retardant drop occurred coincident with the tree strikes. Seconds later, the aircraft entered a left-hand spin and collided with terrain. A post-impact explosion and fire consumed much of the wreckage. The on-board emergency locator transmitter did not transmit a signal and was not recovered.
Investigation Findings
The investigation determined that both engines were delivering maximum power and both propellers operated normally. There were no identifiable in-flight airframe failures or system malfunctions. The crew did not communicate any concerns or attempt to abort the bombing run. The landing lights and flap setting indicated the BOMBING CHECK checklist had been completed. The partial retardant drop confirmed the hydraulic system was pressurized and operating normally. Since the drop button could only be operated from the left seat, its operation confirmed the captain was not incapacitated.
The aircraft had descended more than 400 feet early in the circuit and was climbing slowly toward the edge of the ravine. The investigation could not determine exactly how tree damage affected controllability. A left turn down the ravine was the only exit route after striking trees, but it was not determined if the crew initiated the turn or if it was a consequence of damage or a go-around attempt.
Operational Factors
In the absence of flight data and cockpit voice recorders, the investigation examined two possible operational factors: a low energy condition and a visual illusion. The slow climb, rising terrain, and lack of a good horizon reference were criteria that could contribute to a low energy condition, which may not have allowed sufficient time to establish an adequate climb despite engine power. Airspeed and angle-of-attack indicators should have provided indications, but there was no audible or visual alert.
A visual illusion may have affected the crew's ability to recognize the aircraft's flight path relative to rising terrain. The flight occurred during the last hour of daylight with growing shadows and smoke, factors that affect visibility. The bird dog pilot had the benefit of flying consecutive lower circuits, which may have reduced the likelihood of such an illusion. Illusions were not discussed in briefings to the tanker crew.
Emergency Drop System
The crew likely recognized a collision was imminent very late. The entire retardant load was not jettisoned. Factors that may have influenced this include the visual illusion, lack of emergency-drop training for the first officer, and the location of the emergency-drop selector requiring significant diversion of attention. Company procedures required captain initiation for load jettison. Additionally, there was no requirement for flight crews to test the emergency-drop system once the fire season began.