The pilot of an ultra-light helicopter was killed when the aircraft crashed southeast of Calgary on Sunday.

The aircraft came down Sunday around 5:30 p.m. on the banks of the Highwood River near the Davisburg Bridge on Highway 552, RCMP said in a release.

Fishermen who saw the crash called 911.

The pilot, whose name has not been released, was the only person on board and died at the scene.

A release from the Transportation Safety Board of Canada (TSB) described the helicopter as "amateur built."

The TSB says two investigators from Edmonton will examine the crash site Monday and determine if a full investigation is needed. A TSB spokesperson said it doesn't investigate crashes involving ultra-light helicopters very often.

Jason Arthur, safety manager for the Mount Royal University aviation program, said it may be difficult to determine a cause of the crash, but it shouldn't be impossible.

"It's quite hard to do that sometimes, in these cases where the aircraft don't have a flight data recorder on board," he said.

"But the TSB, they're very capable at what they do, so they're able to piece together very complicated puzzles and determine, a lot of times, what the actual cause was."

Area resident Robert Graves said he and some friends were sitting in the river valley nearby when they heard what sounded like a car crash.

"We were just taking it easy, sitting beside the river in lawn chairs, and all of a sudden there was a great big bang. We thought someone crashed into the bridge, but we couldn't see anything," he said.

"So we just dismissed it until we started hearing all the fire trucks show up."