Photo: The Canadian Press

An accident investigator says it will be challenging to determine exactly what caused a plane crash that killed two flight instructors from Calgary's Mount Royal University.

Fred Burow of the Transportation Safety Board says the plane's major components were destroyed in the crash and the resulting fire. The aircraft also wasn't carrying — nor was it required to carry — a cockpit voice recorder or a flight data recorder.

"The absence of these recorders does make the investigation more challenging," Burow said Monday at a briefing in Edmonton. "The so-called black boxes that are required in larger aircraft do make things easier for the investigation and do bring a lot more data to it."

Pilot Jeffrey Bird and co-pilot Reynold Johnson died Feb. 13 when their twin-engine Tecnam aircraft went down northwest of Calgary.

Burow said it's too early to say whether the crash was caused by mechanical failure or a medical issue with one of the pilots. Investigators are still sifting through the wreckage and Burow says the aircraft's maintenance history has been requested.

"I'd like to stress if, during the investigation, there are any safety concerns that have to be dealt with immediately, we co-ordinate that with the regulator — Transport Canada — the manufacturer and we get that information out right away," he said. "At this time, we don't have anything like that."

Mount Royal University said in a statement it is continuing to co-operate with the Transportation Safety Board, as well as provide support to all students and instructors affected.