MINNEAPOLIS, AUG. 20 -- A jury today convicted three former Northwest Airlines pilots of flying while intoxicated, rejecting defense claims that the smoothness of the 91-passenger flight proved that they were not impaired.

The convictions were the first under a 1986 federal law cracking down on drinking and drug use in commercial transportation, said Assistant U.S. Attorney Elizabeth de la Vega.

"The impact of the trial was more than the verdict," she said. "With the attention it's been given for months, it's had an impact on pilots."

The felony conviction carries a possible maximum sentence of 15 years in prison and a fine of up to $250,000. However, de la Vega said sentencing guidelines call for prison terms of 12 to 18 months.

"I came into this expecting the worst, so in that sense I had no surprise," said former captain Norman Lyle Prouse, who testified that he drank as many as 20 rum and diet sodas at a lounge the night before Flight 650 left Fargo, N.D., March 8.

The Boeing 727 landed safely at the Minneapolis-St. Paul International Airport, where the pilots were arrested. A customer who argued with one of the pilots at the lounge had reported them to the Federal Aviation Administration.

Prouse, 51, of Conyers, Ga.; 1st Officer Robert Kirchner, 36, of Highland Ranch, Colo.; and flight engineer Joseph Balzer, 35, of Antioch, Tenn., each were convicted of one count of operating a common carrier while under the influence of alcohol or drugs.

U.S. District Judge James Rosenbaum ordered a pre-sentence investigation and released the defendants on their own recognizance.

A waitress at the Speak Easy lounge in Moorhead, Minn., adjacent to Fargo, testified that Prouse fell as he left the bar at about 11:30 p.m. and returned to ask directions to his hotel, which was about three blocks away.

Balzer and Kirchner shared at least six pitchers of beer and left the bar about an hour before Prouse, according to testimony.

The plane left at 6:30 the next morning.

Prouse, an acknowledged alcoholic who entered a treatment program after his arrest, said he had little hope of flying again. Balzer was more optimistic.

"It's kind of hard to keep a good pilot on the ground," Balzer said. "That's kind of like asking Picasso if he were going to paint again."

The federal law against flying under the influence of alcohol does not define drunkenness as a specific blood-alcohol level, as many state laws do. However, it suggests that a pilot with a blood-alcohol content of 0.1 percent would be impaired. The law, adopted in 1986 and amended in 1988, also applies to those controlling commercial boats, trains and passenger-carrying buses.

In tests about two hours after the plane landed, Prouse had a blood-alcohol concentration of 0.13 percent, Kirchner's was 0.06 percent and Balzer's was 0.08 percent.

Defense lawyers said the smoothness of the 40-minute flight proved the pilots were not impaired. But de la Vega questioned whether they could have handled an emergency.

Herbert Moskowitz, a behavioral scientist, testified for the prosecution that as little as half a can of beer can cause delayed reactions. A blood-alcohol concentration of 0.03 percent can cause significant impairment, he testified.

Jurors deliberated about nine hours.

Northwest fired all three pilots for drinking within 12 hours of a scheduled flight, and the FAA revoked their licenses. The agency forbids pilots from flying within eight hours of drinking or with a blood-alcohol content of 0.04 percent or more.