A lawyer for one of two U.S. pilots who released a bomb over southern Afghanistan in April, accidentally killing four Canadian soldiers, says the Air Force had pressured the pilots to take amphetamines that may have impaired their judgment during the mission.

Majs. Harry Schmidt and William Umbach face a possible court-martial for dropping the laser-guided bomb near Kandahar on April 17. An Air Force investigation determined the pilots "demonstrated poor airmanship" and ignored standard procedure by not making sure there were no allied troops in the area.

But Umbach's lawyer, David Beck, said he would show at a Jan. 13 hearing on whether to court-martial the pilots that the Air Force routinely pressures pilots to take dexamphetamine, a prescription drug also known as "go pills." He said the drug can impair judgment and is not recommended for people operating heavy equipment.

Beck said the Air Force prevents pilots from flying if they refuse to take the pills.

Air Force spokeswoman Lt. Jennifer Ferrau acknowledged the pills are used as a "fatigue management tool" to help pilots stay alert through long missions. But she said use of the pills is voluntary, and that their effects have been thoroughly tested.

"There have been decades of study on their efficacy and practicality," she said. "The surgeon general worked very closely with commanders on this."

Beck and Charles W. Gittins, Schmidt's lawyer, said the Air Force's investigation is full of errors. Beck said the pilots were not told in advance that allies were holding combat exercises, and that Schmidt dropped the bomb in self-defense after seeing gunfire on the ground.

"What happened was a terrible tragedy. You don't honor (the victims) by wrongfully prosecuting these pilots," Beck said. "This is political appeasement of Canadians who are angry."

Ferrau said Air Force officials would not comment on specifics of the case.

On the night of the bombing, 15 Canadian soldiers were practicing anti-tank attacks with live ammunition at Tarnak Farm, a former al-Qaida training camp. A Canadian report said the soldiers were using firearms ranging from sidearms to shoulder-fired anti-tank weapons.

Schmidt and Umbach were flying F-16s toward their base after six hours of a mission in which "no significant events occurred," the Air Force report said.

Just after midnight, they spotted gunfire on the ground and reported it to flight controllers. One of the pilots asked for permission to fire his 20 millimeter cannon and was told to wait, according to the Air Force investigators' report.

Sixteen seconds later, Schmidt reported surface-to-air fire and said he was going to "roll in," or attack the shooters.

"I've got some men on a road and it looks like a piece of artillery firing at us," Umbach said, according to the report. "I am rolling in, in self defense."

Schmidt released the bomb, which landed about three feet from a Canadian machine gun crew. Killed instantly were Sgt. Marc Leger, Cpl. Ainsworth Dyer, Pvt. Richard Green and Pvt. Nathan Smith.

The Air Force report said Schmidt soon asked controllers, "Can you confirm that they were shooting at us?"

The controller did not answer, but said "friendlies" could be on the ground nearby, the report said. The controller told Schmidt and Umbach to return to their base.

Air Force investigators concluded that Schmidt and Umbach should have left the area when they spotted gunfire to allow time to determine its source. Remaining in the area led to the pilots' misperception that they were under attack, the investigators said.

But the pilots' lawyers said Schmidt and Umbach had good reason to believe they were being attacked. Beck said it's unusual for troops to conduct night exercises in a combat zone.

"How dare you do a training exercise at night in a combat zone?" Beck said. "And how dare you not tell the pilots?"

The deaths, Canada's first combat fatalities since the Korean War, sparked anger among many Canadians, some of whom questioned their country's role in the American-led war on terrorism.

Beck said Air Force officers should take the blame, because their communications system did not inform the pilots that the gunfire came from allies.

After the hearing, a recommendation on whether to court-martial the pilots will be delivered to Lt. Gen. Bruce Carlson, commander of the 8th Air Force, who will make the final decision.

Schmidt and Umbach face charges of involuntary manslaughter, aggravated assault and dereliction of duty. If convicted of all charges, they face a maximum of 64 years in military prison.