The Transportation Safety Board of Canada (TSB) focused on pilot safety and maintenance as it published its report into a helicopter crash in the Sahtu in February.
The accident happened on the morning of February 15 at a helipad on Bear Rock, just outside Tulita. The helicopter – operated by Sahtu Helicopters, a subsidiary of Great Slave Helicopters – fell to earth shortly after take-off, coming to rest 50 metres downslope from its initial location.
The pilot, who was not wearing a helmet, was seriously injured and helped by their passenger until assistance arrived in the form of another helicopter almost four hours later.
In its report, the TSB examines ground resonance as a probable cause of the accident.
Ground resonance is a mechanical issue whereby the rotor system on the helicopter becomes unbalanced, increasing vibrations within the airframe. The effect, which is somewhat like a lopsided load of laundry in a washing machine, destabilizes the aircraft.
Not all helicopters are equally susceptible to ground resonance. On models where ground resonance is more likely – which depends on the type of rotor system used – damper systems act as a controlling measure.
Investigators reported one of the Sahtu Helicopters aircraft’s damper assemblies did not immediately pass tests following the accident, but was “found to be serviceable” once it had been disassembled, cleaned, and reassembled with some new parts.
The report said Great Slave Helicopters, which was in charge of maintaining the helicopter, should have done a better job of logging its maintenance work on the aircraft – and could have followed up on early signs of an unusual vibration.
Four days before the accident, the report stated, an engineer had removed the helicopter’s main rotor blades. When they were reinstalled a day later, the same pilot conducted a test run “during which vibrations were noted.”
The report continued: “The vibration levels were not verified using vibration analysis equipment, which was available at the maintenance hangar. The blade tip tracking and dynamic balancing were not checked, as prescribed in the aircraft maintenance manual.
“When this type of work is carried out, the Canadian Aviation Regulations and company policies require that an entry be made in the aircraft journey log; however, no entry was made in the aircraft journey log for either the removal or the installation of the rotor blades. 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 pilot subsequently flew the helicopter for six hours before the occurrence and the vibration continued. During this time, no action was taken to verify or rectify the vibration and no aircraft journey log entries were made.”
The TSB report did not expressly censure the helicopter company nor any individual involved, but did recommend the thorough recording of all maintenance work, following prescribed maintenance procedures, and wearing a helmet as a pilot (though this is not a requirement).
According to the TSB, Great Slave Helicopters has subsequently instructed staff to ensure similar maintenance work is appropriately recorded; installed an additional audit step to monitor the removal and reinstallation of helicopter blades; and reminded pilots to record “any sudden changes in vibration levels” in an aircraft’s journey log.