A pilot who thought the planet Venus was a plane after waking up from a nap, took his airliner on a nosedive towards the Atlantic to avoid what he thought was a "collision".

Pilot fatigue to blame for plane's mid-flight dive (R)

Sixteen passengers and crew were hurt in the incident on an Air Canada flight, after the first officer tried to avoid a US military plane that he wrongly thought was heading straight toward him.

An official report found that the co-pilot was suffering from "sleep inertia" after waking up from a long nap, and was disorientated when he took control of the plane.

The plane, which was en route from Toronto to Zurich, dived 120m before the captain took control. Passengers who weren't wearing their seatbelts were thrown from their seats.

"The first officer initially mistook the planet Venus for an aircraft," said the report.

According to the investigation, the "confused and disoriented" co-pilot then thought that a US military plane flying 300m metres below was heading directly for his plane. "He reacted to the perceived imminent collision by pushing forward on the control column," the report read.

"Under the effects of significant sleep inertia (when performance and situational awareness are degraded immediately after waking up), the first officer perceived the oncoming aircraft as being on a collision course and began a descent to avoid it," Canada's Transportation Safety Board said.

Challenge of managing fatigue

Chief investigator Jon Lee said the incident underscores the challenge of managing fatigue on the flight deck.

Pilots are permitted to nap for 40 minutes at a time on long flights, as laid down by airline regulations.

However the first officer responsible for the dive towards the Atlantic, whose sleep is reportedly interrupted by young children at home, had been sleeping for 75 minutes, which meant that he fell into a deep sleep and was disorientated when he woke up.

Air Canada said it had taken steps to prevent similar incidents from happening again. In a statement, it reminded pilots to follow the rules for napping during flights and increasing efforts to heighten crews' awareness of fatigue and its effects.

"Air Canada has developed a special fatigue report form for use in its safety reporting system ... this enhanced system should be in place in summer of 2012," said spokesman Peter Fitzpatrick.

However the Air Canada Pilots Association has criticised the current regulations and asked authorities to take the stresses of night flying into account when setting the maximum hours a pilot can work.