A report released April 16 by the Transportation Safety Board says that poor rest led an Air Canada pilot to make a sudden and hazardous descent during flight ACC878 from Toronto to Zurich in January 2011.

According to the TSB report, about halfway through the flight the plane’s captain made a position report that awoke the first officer, who had been taking an authorized rest nearby.

In his grogginess, the report says the first officer misjudged the path of an oncoming aircraft and pushed the control column forward, resulting in an abrupt change of altitude that pitched the Air Canada plane and caused injury to 14 passengers and two flight crew.

'This occurrence underscores the challenge of managing fatigue on the flight deck.'—Jon Lee, lead investigator

While technology has greatly improved the safety and efficiency of air travel, pilots are still susceptible to the physical stresses of flying.

Working for long hours while passing through different time zones can disrupt the human body's circadian rhythms and affect performance.

In addition to that, pilots must contend with dehydration, which can also lead to drowsiness. Because the plane is pressurized, the air is very dry and can sap moisture from the body, which is why pilots must take steps to consume ample amounts of water while in the air.

'Sleep inertia'

What the first officer on that Air Canada flight was dealing with specifically was something called "sleep inertia."

"Sleep inertia is a very disorienting, very confusing feeling that occurs right as people transition from sleep to wakefulness," says Dr. Elliott Lee, a specialist in the sleep clinic at The Royal Ottawa Mental Health Centre.

Dr. Lee says that sleep inertia is provoked by several factors, including how much time the person has been awake prior to the sleep period, and what stage of sleep they're in when they awake.

"If they're in light sleep and they wake up, sleep inertia is limited. But if they're in deep sleep, that's where sleep inertia will become more prominent," he says.

Power-napping in mid-flight

The pilot of the Air Canada flight was taking what is known as "controlled rest," which is essentially an unscheduled but authorized power nap. Air Canada's flight operations manual states that each rest period should not exceed 40 minutes, to specifically avoid sleep inertia.

According to the TSB report, the first officer on ACC878 had been asleep for 75 minutes.

Air Canada's flight operations manual also allows pilots 15 minutes after napping in order to recuperate from sleep inertia.

Dr. Lee contends this may not be enough. "It would be ideal to have 30 minutes to an hour to have appropriate time to recover from the previous sleep."

According to the Air Line Pilots Association International, which represents more than 53,000 pilots at 37 U.S. and Canadian airlines, pilot fatigue can have the following symptoms:

  • Forgetfulness
  • Poor decisions/mistakes
  • Slowed reaction time
  • Reduced vigilance
  • Poor communication
  • Fixation
  • Lethargy/complacency
  • Bad mood
  • Nodding off

Flight crew schedules

To maintain flight safety, airlines schedule larger crews for longer flights. Every flight, no matter the duration, has at least two pilots, but longer haul flights can have one or two additional pilots, sometimes called international relief officers (IROs), to split up the workload and allow rest breaks.

Before a flight departs, the captain and crew agree on how to divide the load between them, making sure to take rest periods into account.

According to Air Canada's flight operations manual, only one pilot can rest at a time. Furthermore, each rest period should not exceed 40 minutes, a measure specifically intended to avoid sleep inertia.

The area of the plane where pilots can rest varies from airline to airline. Some airlines have specially designated bunks inside the cockpit, others may section off a seat in first class, and some have larger rest areas for crew located at the rear of the plane.