Summary
At about 1210 mountain standard time (MST), Tanker 86, a four-engine Lockheed L-188 Electra (registration C-GFQA, serial number 188A-1040), departed Runway 16 at Cranbrook Airport, British Columbia, with two pilots on board. The aircraft was tasked with a fire-management mission on a small ground fire (designated N10156) located two nautical miles southwest of the township of Cranbrook. Seven minutes earlier, a partner "bird dog" aircraft, a Turbo Commander, had also departed Cranbrook to assess appropriate flight path profiles and to establish a suitable fire-retardant delivery program.
Flight History
Following flight path demonstrations by the bird dog aircraft, Tanker 86 proceeded to carry out the retardant drop on the fire. After delivering the specified retardant load, the Electra was seen to turn right initially, then entered a turn to the left. At 1221 MST, the aircraft struck the terrain on the side of a steep ridge at approximately 3900 feet above sea level. The aircraft exploded on impact, and the two pilots were fatally injured. An intense post-crash fire consumed much of the wreckage and started a forest fire at the crash site and surrounding area. The on-board emergency locator transmitter was damaged by impact forces and did not activate.
Bird Dog Aircraft and Flight Planning
On board the Turbo Commander were its pilot and two air attack officers (AAOs) from the British Columbia Forest Service (BCFS). The AAO function includes assessing ground fire characteristics and devising effective and safe flight paths, retardant dispersal patterns, and delivery profiles. The bird dog pilot provides operational flight performance input to help the AAO plan and coordinate the attack. In the minutes leading up to the accident, the bird dog aircraft flew an approximate route while the AAOs determined that two separate retardant drops forming a "V" were required, with an altitude over the drop zone of 3700 feet above sea level. Since a straight-out exit from the first run (heading of about 155° magnetic) would take the Electra into rising terrain, the AAOs decided the safest exit route after the drop was a 35-degree right turn into a wide, substantially flatter valley toward Moyie Lake. High-tension electrical power lines crossed beneath the exit route but were lower than the proposed flight path.
Investigation Findings
Examination of the wreckage, as far as possible given the destruction, found no evidence of system malfunction or pre-existing defect. All flight control surfaces were accounted for, with no sign of in-flight detachment or malfunction. Sightings of the aircraft seconds before impact confirmed it was intact, without fire, with all engines operating, and with hydraulic and electrical systems functioning. The fact that the pilot flying released two loads before impact indicates he was conscious and aware of the situation. No communication or witness accounts suggested a flight control malfunction. The low rate of climb, in the absence of mechanical reason, suggests the pilots were not aware of their proximity to rising terrain.
Calculations of the aircraft's turn radius for various airspeeds showed that the most likely airspeed-bank combinations were 135–150 knots and 40–45 degrees, consistent with purposely controlled flight. The exit route toward Moyie Lake was always available. Since the aircraft did not deviate from its arcing path to the left, it is unlikely the pilots were dealing with a situation preventing climb performance or a flight control malfunction. Engine and propeller examinations consistently showed engines delivering similar and high power at impact. Performance assessments revealed the Electra could have attained climb rates of around 1000 feet per minute at any stage during the left turn. No mechanical reason, aerodynamic effect, or performance factor was found that would have prevented the aircraft from attaining sufficient altitude to avoid the terrain.
Without mechanical defect or performance inadequacy, the explanation becomes one of human performance. The pilots likely flew a vertical profile after the drop, climbing from 3700 to at least 3900 feet. It could not be determined if the aircraft climbed more and then lost altitude. Possibly, after initiating a satisfactory climb rate, the pilots became distracted and unintentionally allowed the climb to deteriorate. However, the reason for not climbing cannot be identified with certainty.
Documented research indicates that mountainous terrain in daylight, especially at midday with little shadow, lacks effective visual definition, making it difficult for pilots to assess slope, proximity, and rate of closure. In this accident, terrain characteristics were similarly difficult to assess. It is most likely the Electra pilots were deceived by the apparently gently sloping terrain and did not detect the ridgeline crossing their flight path until too late. Compounding this were limitations from the left bank reducing perspective and field of vision, and cockpit windshield dimensions. The pilots were likely unaware of the collision path until the last seconds; otherwise, they would have altered course toward the valley.
Probable Cause
According to the investigation, for undetermined reasons, the Electra did not climb sufficiently to avoid striking the rising terrain. Additional contributing factors included the deceptive terrain characteristics and the chosen flight path and rate of climb that made collision unavoidable.
Safety Actions Taken
The British Columbia Forest Service (BCFS) conducted an internal examination and found that flight operations practices were in accordance with the Firebombing Procedures Manual, except that the Electra turned left before attaining sufficient altitude. Recommendations included reinforcing training so that tanker pilots advise bird dog crews if deviating from demonstrated routes, focusing training on safety procedures and potential risks, and incorporating practical use of emergency dump systems. Crew Resource Management (CRM) training had been introduced in 1993, with no serious injury occurring since then.