The Transportation Safety Board of Canada (TSB) is recommending that Transport Canada work with the aviation industry and employee representatives to develop and implement requirements for a comprehensive substance abuse programme to reduce the risk of impairment of persons while engaged in safety-sensitive functions.

The details are in the investigation report (A15P0081) released yesterday into the fatal 2015 in-flight breakup of a cargo aircraft operated by Carson Air Ltd.

On 13 April 2015, the Carson Air Swearingen SA-226-TC Metro II was carrying freight from Vancouver International Airport to Prince George Airport, British Columbia, with a crew of two pilots on board.

About six minutes after departure, the aircraft disappeared from radar. Its last known position was approximately 15 nautical miles north of the airport at an altitude of about 7500 feet.

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Ground searchers found aircraft wreckage on steep, mountainous, snow-covered terrain later in the day.

The aircraft had experienced a catastrophic in-flight breakup. Both the captain and first officer were fatally injured, and the aircraft was destroyed.

The investigation determined that the aircraft entered a steep dive, then accelerated to a high speed which exceeded the aircraft's structural limits and led to an in-flight breakup.

Subsequent toxicology testing indicated that the captain had consumed a significant amount of alcohol on the day of the occurrence. As a result, alcohol intoxication almost certainly played a role in the events leading up to the accident.

"In Canada, regulations and company rules prohibit flying while impaired, but they rely heavily on self-policing," said Kathy Fox, Chair of the TSB.

"What is needed is a comprehensive substance abuse programme that would include mandatory testing as well as complementary initiatives such as education, employee assistance, rehabilitation and peer support."

"We realise that employees within Canada's aviation industry will have concerns under any possible testing regime," added Chair Fox.

"This is why we recommend that the substance abuse program consider and balance the need to incorporate human rights principles enshrined in the Canadian Human Rights Act with the responsibility to protect public safety."

Pilot incapacitation is one of three scenarios which the TSB has not ruled out to explain the possible events that led to the accident. It is also possible that the heaters of the pitot system, which provides airspeed information, were off or malfunctioned.

The third scenario involves a number of flight-specific factors that are consistent with an intentional act.

However, without objective data from a cockpit voice recorder or flight data recorder, it is impossible to determine with certainty which scenario played out during the occurrence flight.

The TSB has previously recommended (A13-01) the installation of lightweight flight recording systems aboard smaller commercial aircraft and flight data monitoring by smaller commercial operators, both to advance transportation safety and to provide data to investigators following an occurrence.