The U.S. Department of Transportation announced a new regulation Monday that limits the amount of time passengers can be kept waiting on the tarmac. Consumer advocates who have pushed for more passenger protections have welcomed the move but can travelers really stop worrying about getting trapped on board?

The new regulation says that airlines can t allow a domestic flight to remain on the tarmac for more than three hours after it leaves the gate or touches down without allowing passengers to disembark. (Carriers operating international flights have to specify a time limit for deplaning passengers.) Airlines are required to maintain functioning lavatory facilities and provide food and water after two hours of waiting. The Department of Transportation can assess a fine of up to $27,500 for each violation of these new rules potentially subjecting airlines to a fine for each passenger on a plane that was kept on the tarmac past the three-hour limit.

But there are exceptions and it s possible they re big enough to fly a 747 through. Airlines can escape the wrath of the three-hour rule in the event of safety or security concerns, or if air traffic control determines that deplaning passengers would disrupt airport operations. Allowing passengers to be held on the tarmac for more than three hours if air traffic control deems it necessary is a significant loophole in the time limit rule, and the new regulation doesn t add anything to consumers ability to get compensation for delays or long waits, says Mark Kelley Schwartz, an attorney who specializes in representing airline passengers.

Perhaps more significant for many travelers is another aspect of the new regulation: a requirement that airlines disclose more information about delays on their web sites, including highlighting any flights that are chronically delayed defined as a flight that s more than half an hour late more than half of the time. The Department of Transportation will consider operating a flight that s chronically delayed for four consecutive months to be an unfair and deceptive practice on the part of an airline. That rule on chronically delayed flights could have an impact, because there are federal penalties in place for engaging in unfair and deceptive practices, says Schwartz.

Still, consumer advocates are celebrating the new rules after pushing for such changes for years. I think fliers everywhere should be grateful to this administration for protecting their rights, says Kate Hanni, a spokeswoman for the Coalition for an Airline Passengers' Bill of Rights, who says she was stuck on the tarmac for nine hours in December 2006. More remains to be done to make sure the new rules are fully enforceable, but this is a critical first step, Hanni says.