A fatal helicopter crash at a drill site near the Hope Bay gold mine last September happened after the pilot let go of part of the flight controls and leaned out to check the tail, an investigation has found.

The helicopter crashed on Sept. 14 at an exploration drilling site 13 kilometres away from the Hope Bay mine. The mine is about 125 kilometres southwest of Cambridge Bay.

The crash killed a 42-year-old employee who was on the ground. The pilot was not injured.

The Transportation Safety Board of Canada issued its final report on the crash Wednesday. The report doesn't make recommendations or find fault, but it does lay out the facts in an effort to prevent future safety issues.

The report says the helicopter experienced a "dynamic rollover" when it crashed on Sept. 14. That type of rollover happens when the helicopter is at an angle and starts rotating around one of its landing gear instead of its centre of gravity.

It doesn't take much for the roll to become unstoppable, the report states — just an average angle of 15 to 17 degrees.

The helicopter was doing a series of flights that day to move people and equipment to the Hope Bay mine area.

While the helicopter's weight and balance weren't off when it crashed, both the pilot and a cargo basket were on the right side of the machine — the direction it rolled. There was also a wind coming from the left.

The ground the helicopter landed on that day was uneven, the report noted. As the pilot was landing, he noticed the driller who was waiting for him looking at the helicopter's tail area, making him worry that the tail might hit upsloping terrain.

When he had landed, he let go of the collective lever — which alters the pitch of all main rotor blades — and leaned out the right door to check the tail.

"While the pilot's head was turned, the helicopter began to roll over on its right side, and the pilot attempted to regain a hold of the collective," the report stated.

The collective lever, if lowered, can help correct a dynamic rollover before it goes too far.

The main rotor blades broke against the ground. Debris, which flew up to 21 metres away, hit the driller on the ground and killed him.

The report includes a safety message about how important it is for helicopter pilots to "be vigilant" with flight controls when on the ground.

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