The U.S. Transportation Department's fining last week of the three airlines responsible for keeping 47 passengers confined on a plane for hours under very unpleasant conditions brings some satisfaction. But the fines alone are inadequate to curb airlines' disregard for their customers' well-being.

Only an act of Congress or other binding federal regulation is going to force airlines to let passengers off planes that are grounded for hours.

Fines of $50,000 each were levied against Continental Airlines and ExpressJet Airlines, the company that operated Continental Flight 2816. The flight left Houston Aug. 7 for Minneapolis but was diverted to Rochester International Airport in Minnesota because of severe thunderstorms. Passengers were kept on the plane for nearly six hours, despite the pilot's repeated requests to ground crews of Mesaba Airlines to let them disembark. They finally were allowed into the terminal, only to return later to the same plane, with unusable restrooms, and be flown to Minneapolis.

Mesaba Airlines, which was fined $75,000, was the only airline with staff at the airport at the time and told the pilot that because no Transportation Security Administration screeners were on duty, passengers could not enter the terminal. This was false, because federal rules permit passengers to enter an airport as long as they are kept in secured areas.

In fact, passengers of a Delta Air Lines flight diverted to Rochester were allowed to leave their plane at about 3:30 a.m. Mesaba is a subsidiary of Northwest Airlines, itself a subsidiary of Delta. And a bus took passengers from an earlier diverted flight to their destination in Minneapolis, less than 90 miles away.

The fines against the three airlines were for "unfair and deceptive practices": Mesaba gave wrong information and the other two airlines violated Continental's customer-service promise to remove passengers as soon as possible when planes are expected to be grounded longer than three hours.