Pilot fatigue has been cited as a factor in the sudden dive of an Air Canada plane last year that injured 16 people.
A Transportation Safety Board report published Monday looks into the sharp, sudden descent of Flight 878 as it flew over the Atlantic Ocean on Jan. 13, 2011.
The Boeing 767 plane, which was travelling from Toronto to Zurich, dipped several hundred feet from its assigned altitude before the captain was able to pull it up again.
In its report, the TSB says the plane began its abrupt descent after a first officer spotted an oncoming aircraft and mistakenly perceived it to be on a collision course with the Air Canada flight.
The first officer, who had just woken up from a scheduled nap, took action to avoid what he or she believed was a potential collision.
The pilot also initially mistook the planet Venus for another plane, the report said.
"As the oncoming aircraft safely passed underneath, the captain regained control," the report said.
Fourteen passengers and two flight attendants, who were not wearing seatbelts, were injured during the brief but turbulent incident.
According to the TSB, the seatbelt sign was on in the 40 minutes leading up to the incident.
"This occurrence underscores the challenge of managing fatigue on the flight deck," lead TSB investigator John Lee said in a release. "It also shows that in-flight passenger injuries can be prevented by wearing seatbelts at all times while seated."
It's common for pilots and crew members to take short, scheduled naps to combat fatigue during long flights.
But the Air Canada Pilots Association said Ottawa should instead mandate that eastbound transatlantic flights be staffed with three pilots.
Association president Capt. Paul Strachan said having three pilots in the cockpit would allow each one of them to leave for a proper rest, instead of relying on 40-minute naps.
"What if something happens to the other pilot during that 40 minutes?" he said. "The only reason there isn't a third pilot on that flight is so they don't have to pay a third pilot."
The new details resurrect old questions about the effectiveness of controlled rest periods and other methods intended to battle fatigue.
U.S. airlines fly the transatlantic route with three pilots and even India's in-flight rest rules are stricter, Strachan said.
"Canada's regulations are stark in their insensitivity to the science of fatigue," he said.
Also contributing to the Flight 878 incident was "prior fatigue" and the fact that the officer slept longer than his allotted napping time, the TSB said.
Another contributing factor was that the crews "did not fully understand the risks associated with the fatigue or the procedures for conducting controlled rest," the TSB said.
The report says that the incident has spurred both Air Canada and its pilots association to better understand pilot fatigue, especially on flights travelling from North America to Europe.
