Rotor problem caused helicopter to crash down mountain near Tulita
An accident in which a helicopter fell down the side of a mountain near Tulita, N.W.T., seriously injuring the pilot, was caused by a number of factors, says a report by the federal Transportation Safety Board.
The Sahtu Helicopters aircraft was being operated by Great Slave Helicopters when it crashed on the morning of Feb. 15.
The pilot had safely flown one passenger from Norman Wells, N.W.T., to the telecommunications tower on Bear Rock.
But during a second engine-run, the report says, the helicopter lifted several feet off the helipad, rotated to the left and drifted 30 metres to the southeast. It then hit the ground and came to rest 50 metres downslope of the helipad.
The pilot was wearing a lap and shoulder harness at the time, but not a helmet. He was seriously injured but able to leave the helicopter and receive first aid from the passenger.
A few hours later, he was taken by another helicopter to Yellowknife for medical care.
The report, released last month, says when the pilot increased the throttle, the helicopter began bucking backward and forward on the landing gear skids.
The pilot then decided to lift off to stop what he thought was ground resonance — an imbalance in the rotation of the helicopter rotor.
Before the helicopter became airborne, the fuel control level was not locked into the flight position, and neither the main rotor revolutions per minute (RPM) nor the engine RPM accelerated to the flight-governing range, the report says. The rotor RPM then dropped and the pilot lost control.
What caused the crash?
Lead investigator Mike Adam said this, ground resonance on the helipad, and vibration in the main rotor system were factors in the crash.
The vibration could have been caused by an out-of-balance rotor blade, Adam said, and while some vibration can be normal, the manufacturer's airframe maintenance model details vibration limits.
Four nights before the accident, the report says, the helicopter was in the Great Slave Helicopters' hangar, where the main rotor blades were removed and reinstalled and the vibration was noted.
But the vibration levels were not verified using vibration analysis equipment and it was not documented in the aircraft journey log as required.
"The investigation found that it was the maintenance provider's routine practice to do this type of work without making entries in the aircraft journey log," the report states in part.
Adam noted that the investigation was limited, as the helicopter doesn't have flight data recording devices and was also damaged in the crash.
Company responds
Alisdair Martin, president of Great Slave Helicopters, said the company takes these reports seriously and it has responded with a number of safety measures.
"It's a fresh set of eyes coming and looking at all the evidence," he said. "Anything you can learn out of an incidence like this, you should and we do."
The report says on June 16 company management sent an email to all company pilots and aircraft maintenance engineers, reminding them of the journey log requirements. An audit cycle was also added to monitor blade removal and installation.
Martin said the pilot has since returned to work but has not resumed flying yet, as his arm is still recovering from being injured in the crash.
