A recent report detailing the events of a backcountry helicopter crash north of Nelson in March points to the cumulative effects of weather in the mishap.
The Transportation Safety Board of Canada (TSB) released a seven-page report Nov. 2 on the March 16 tail rotor strike and roll over of an Airbus Helicopters AS350 B3 helicopter in the Kootenay Valley, 35 NM north of Nelson.
The TSB conducted the limited-scope investigation into the incident “to advance transportation safety through greater awareness of potential safety issues,” the report stated. The function of the board is not to assign fault or determine civil or criminal liability.
The culprit, in fact, was weather, the report found.
“The accident occurred in an area known for weather conditions associated with mountainous terrain,” it read. “Flying conditions can be harsh, and abrupt variations in weather are not uncommon.”
The closest aviation weather reporting station was Revelstoke Aerodrome (CYRV), located 65 NM northwest of the accident site.
The airbus from Kootenay Valley Helicopters Ltd. was contracted by the British Columbia Ministry of Transportation and Infrastructure (MOTI) to conduct avalanche control operations north of Nelson Aerodrome with the pilot and two avalanche technicians on board.
According to the report: “The helicopter was hovering near the snow- and ice-covered mountainside when the tail rotor contacted terrain or an object. The pilot immediately performed a forced landing.
“The helicopter impacted the snow pack and rolled over. The tail boom was struck and partially severed by the main rotor blades. All occupants were able to extricate themselves from the wreckage with only minor injuries. Another helicopter nearby retrieved the crew from the mountain.”
Setting the scene
The flight was the second avalanche control flight of the day.
Located in the London Ridge avalanche area, the plan for the day included dropping strategically placed explosive charges — 12.5 kg bags of ammonium nitrate and fuel oil [ANFO] compound — and igniters onto the slope from a height of approximately 20 feet.
The occurrence aircraft took off from the staging area near New Denver under visual flight rules (VFR). The crew were the same as on the first flight, but the avalanche technicians exchanged roles and positions.
However, the sky was overcast with scattered clouds at and below the ridgeline with calm to light winds from the southwest. The helicopter was being operated at an altitude of about 7,000 feet above sea level, approximately 100 feet below the ridgeline.
Source: air transportation safety investigation report A22P0019
From the report:
The pilot and technicians coordinated the placement of the charges and documented whether they detonated and triggered controlled releases of snowpack.
The bombardier was seated on the right side of the rear bench wearing a high-visibility fall-arrest/restraint harness. His role was to deploy charges out of the right- side pocket door.
He coordinated the placement of the helicopter with the pilot to achieve the best effect from the explosive charge. The role of the blasting assistant, who occupied the left front seat, was to document the operation.
The bombardier requested an adjustment to the initial target for the second explosive charge to be deployed, and the pilot climbed the helicopter up the slope, nearer to the ridge and close to the base of the clouds.
The trees in the new location were more sparse and covered with more snow. The pilot assessed the new location and estimated that, as previously anticipated, his exit strategy to turn left and then fly downhill would be appropriate.
As the helicopter progressed along the mountainside near the upper treeline, the pilot positioned and stabilized it in a hover to allow the explosive charge to be deployed.
Just as the pilot lost reference with the ground and flight visibility was reduced, the bombardier deployed the second explosive charge. At this time, the main rotor downwash and prolonged hover over a layer of loose snow created whiteout conditions.
The pilot, with reduced visibility, turned the helicopter to the left. During this manoeuvre the tail rotor contacted either a tree or the surface of the slope; this caused the helicopter to shudder. The high-frequency vibration rapidly worsened and the pilot performed a forced landing.
At approximately 1331, the helicopter landed hard on its skids and tipped onto its right (the pilot’s) side. The main rotor and blades were fractured and the tail boom was partially severed.
The helicopter came to rest about three to five m downslope of the second explosive charge deployed; the charge detonated approximately two-and-a-half minutes later, but did not trigger a release of the snowpack.
Snow entered the cabin through the gap where the pocket door had been removed and through several windows that had broken or popped out. The three occupants were initially disoriented and shaken, but were not injured.
The bombardier was face down in the snow, still secured in the aircraft by his harness, with bags of unprimed ANFO on and around him. The blasting assistant was still belted in the front passenger seat and was disoriented due to being on his side. The pilot secured the electrical and fuel systems, and he, along with the blasting assistant, egressed from the helicopter.
The bombardier required some assistance to release his harness because his own knife was not easily accessible. He also experienced difficulty releasing his lap belt because the latch mechanism had been taped over.
With the assistance of the other crew members, he was released and egressed from the aircraft. The required survival equipment was on board the helicopter; however, because the helicopter was lying on its right side, the cargo door could not be opened and the crew could not access this equipment.
The pilot was able to remove the emergency locator transmitter (ELT) from its housing, attach the remote antenna, and turn it on manually to ensure that it was activated. The signal was received by the Canadian Mission Control Centre and relayed to the Joint Rescue Coordination Centre (JRCC) in Victoria.
The technicians had a portable radio on board, but it was not readily available after the impact. It had been left on top of the instrument panel glare shield and was displaced during the accident sequence.
After approximately a 15-minute search through the snow, it was found. The operator was contacted and informed of the accident, and transportation off the mountain was coordinated.
- Incident excerpt from the report