A helicopter carrying three provincial government workers conducting a wildlife survey was flying at low altitude when it crashed near Camrose, Alta., in January, according to a new report from the Transportation Safety Board of Canada.
The report found that an unintentional right roll preceded the Jan. 23 crash of the Bell 206B helicopter in the woods of Flagstaff County, about 150 kilometers southeast of Edmonton. The three officials and the pilot were taken to hospital but no one died.
The report, released Wednesday, notes that the purpose of the investigation was to advance transportation safety. It does not assign errors or provide recommendations.
According to the TSB report, the aircraft departed Camrose Airfield on January 23 for a series of wildlife survey flights on behalf of the provincial government. It was the sixth consecutive day that they had been held.
Survey flights were generally made at about 300 feet above ground level at a speed of about 90 knots. When observers spotted wildlife, the helicopter would typically slow down, descend, and maneuver at low altitude and slow speed so the animals could be counted and classified.
The flight completed one survey line at 9:20 that day and had gone north to the next.
The report says that around 9:45 a.m., several animals were seen in the bush and the pilot made “a 360-degree left turn descending and decelerating” to allow observers to count and classify. The helicopter was 80 feet above the ground and moving at a speed of about nine knots.
“At this point, the helicopter entered an uncommanded spin to the right,” the report said.
Impact injuries
The pilot tried to regain control of the steering, but the helicopter fell and hit the ground “with little or no forward speed”, and came to rest in a bush. The report said it was upright and largely intact.
The landing skids separated on impact and part of the rear landing skid was pushed into the fuselage, rupturing the airframe, the report said.
“All occupants were seriously injured by the impact forces and were contaminated with jet fuel.”
A passenger called emergency services, which arrived about an hour after the collision and took all four occupants to hospital.
Loss of tail rotor effectiveness
The Bell 206B main rotor blades, viewed from above, rotate clockwise. The rotation creates a torque reaction in the opposite direction, causing the helicopter to steer to the right.
To counteract this, the tail rotor produces a side thrust. According to the report, a pilot applies pressure to the anti-torque pedals to increase or decrease this thrust as needed.
When a yaw movement is not expected, it is called unanticipated yaw or loss of tail rotor effectiveness (LTE).
“Any single-rotor helicopter flying at low speed can experience LTE,” the report says.
“This phenomenon is not related to equipment failure or faulty maintenance; rather, it is the result of the tail rotor not providing enough thrust to maintain directional control.”
Security messages
The investigation determined that the pilot, who had been with Delta since April 2021, was properly licensed and that fatigue was likely not a factor, according to the report.
At the time of the accident, winds were gusting and coming from the left while the turn was being completed.
Four regions of relative wind azimuth are observed to be favorable for an LTE, with both affecting the main and tail rotors during the accident.
In the final safety message section, the report says that certain helicopter operations such as slow-speed wildlife surveys lend themselves to being more at risk of LTE.
“Pilots are reminded that flying an aircraft at low altitude leaves little margin for error and decreases the time and altitude available to effectively manage any unforeseen aircraft condition,” he says.