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Ashley Nunes is an Atlanta-based researcher in transportation safety, regulatory affairs, and behavioural economics.

Two American pilots were arrested last month on suspicion of being under the influence of alcohol prior to a flight. The pair was busted as they prepared to fly 141 passengers on a Boeing 757 from Scotland to the United States. Following the incident, the flight was grounded for hours as the airline arranged for a new crew to be flown in. A spokesman later confirmed the pilots had been removed from all flying duties. The incident comes weeks after two Canadians were arrested on similar charges.

Alcohol and flying don't mix – and can be deadly. In 1977, a DC-8 cargo jet crashed while attempting to takeoff from Anchorage, Alaska. An investigation found the pilot's blood alcohol level to be nearly three times the legal limit. Three decades later, a Boeing 737 crashed while attempting to land in Perm, Russia. The pilot's actions leading up to the crash were found to be inconsistent with specified procedures, something investigators said was most likely caused by the presence of alcohol in the pilot's body.

Such accidents are hardly surprising. Studies show alcohol dulls the senses, affecting everything from attention to speech to vision. Hardly the abilities a pilot can (or wants to) do without. So efforts have been made to keep alcohol out of the cockpit.

Canada, like many countries, requires that at least eight hour pass between a pilot's last drink and reporting for duty. Canadian pilots are also prohibited from flying "while under the influence of alcohol." These measures – we are told – keep the skies safe. The reality, however, isn't so straightforward.

Pilots are bad at judging whether or not they are under the influence of alcohol. Studies show they frequently overestimate how much alcohol they can consume before their blood alcohol level – a common measure of intoxication – increases. They also underestimate how much time must pass for the effects of alcohol to wear off. Simply put, pilots think they can drink more than they should, and are inclined to return to work sooner than they should. Researchers have found these errors to be "more pronounced" for moderate and heavy drinkers, a particularly worrying trend given that alcoholism amongst aviators often tends to be undiscovered and unrecognized.

More importantly, Canadian law does not require that pilots be routinely tested for alcohol offenses. Such tests are usually only administered if a pilot is suspected of being drunk. One former Transport Canada inspector recently noted, "a guy knows he will get away with it unless he gets turned in." This means an intoxicated crew could sit at the controls of a commercial jetliner and fly passengers around until they get caught.

Think it can't happen? In 1990, three Northwest Airlines pilots hit the bar in Fargo, N.D., sharing over 6 pitchers of beer and 15 rum and cokes. The next morning, they flew 91 passengers to Minneapolis. The plane landed safely and the pilots landed in prison, but only after authorities were tipped off that the three were spotted drinking heavily the night before. More recently, a JetBlue pilot was charged with being intoxicated after twice shuttling passengers between New York and Orlando. His blood alcohol was nearly three times the legal limit.

Intoxicated pilots in the cockpit may well be rare. Yet Canada's laws (or lack thereof) make verifying this claim difficult. Our approach seems to be, if it ain't broke, don't fix it.

Recognizing that aviation can be unforgiving of mistakes means adopting routine alcohol testing for all commercial pilots. Canada wouldn't be the first country to do so. But it shouldn't be the last either.

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