OTTAWA - An American pilot may have been tired and struggling with confusing instructions when he opened fire on Canadian troops in Afghanistan last September, killing one and wounding 36, suggests a newly declassified report.

The "lessons learned'' document also suggests an electronic vehicle identification system might have prevented the tragedy.

"Incidents of this nature will always be a reality of combat, however technologies that have not been fully exploited to their full potential exist which could reduce the number of incidents,'' said the report, obtained by The Canadian Press under the Access to Information Act.

The pilot of the A-10 Warthog mistakenly sprayed members of Charles Company, 1st Battalion Royal Canadian Regiment, with Gatling gun fire as they camped at the base of Ma'sum Ghar, a squat, rugged mountain outside of Bazzar-e-Panjwaii.

The three days previous to the accident had seen some of the bloodiest fighting of the newly launched Operation Medusa. Two American attack planes were ordered to repeatedly blitz Taliban positions, near the Canadians, north of the Arghandaub River -- a tense, physically draining type of air operation.

"The two A-10s in this sortie had been strafing the enemy for over three hours and were about to hand over the (air operations),'' says the document.

"The incident occurred in the shift from night to day. This could have been a factor.''

The soldiers, who had lost four comrades through three exhausting days of fighting in an arid vineyard a few hundred metres away from their camp, had just finished breakfast when the air strike happened.

"Most of the company had not yet donned Personal Protective Equipment (body armour and helmets),'' the Sept. 9, 2006, report noted.

The army refused to comment on the document, saying its own board of inquiry investigation was not complete. The status of U.S. Air Force investigation was also unclear.

The heavily censored, six-page Canadian review, stamped secret, pointed to a series of possible contributing factors, including the fact air controllers directed pilots to a reference point "common to both enemy and friendly positions.''

When calling in the overwhelming firepower of the bomb-laden A-10 -- officially called the Thunderbolt but commonly known as the Warthog because of its ugly appearance -- army ground controllers need to give pilots distinguishing landmarks that can be easily identified from the air.

The pilot also misidentified a garbage fire lit by Canadian troops for "fires on the enemy position on the North side of the river,'' the report said, but it's not clear whether the fire was a reference point given by controllers.

Seconds after squeezing the trigger, the U.S. pilot realized the mistake but not before the seven-barrel machine gun had ripped through the company of troops, killed Pte. Mark Anthony Graham, a former Olympic athlete, who had lit the garbage fire.

The report, based on interviews with soldiers, described in gripping detail the efforts of medics, other soldiers and battle group headquarters staff to treat the wounded.

Graham's body "was quietly removed from the scene without the knowledge of other casualties,'' the report said.

In the scramble, rescuers exhausted all of the company and headquarters medical supplies, including bandages, tourniquets and other medical supplies.

As an American Blackhawk helicopter touched down to evacuate the most seriously injured, the Canadians discovered their stretchers -- standard equipment on LAV III armoured vehicles -- were too big to fit into the U.S. aircraft.

"Handles were sawed off in the helicopter landing site in order to get the stretchers with Priority 1 casualties in the helicopter,'' said the report.

An Australian Chinook helicopter soon arrived to evacuate other casualties.

Among other things, the review recommended that NATO allies standardize stretcher sizes, but in the meantime Canadian troops have sawed off the wooden handles on their other stretchers.