A new US Department of Transportation rule "prohibits U.S. airlines operating domestic flights from permitting an aircraft to remain on the tarmac for more than three hours without deplaning passengers," and requires airlines to give trapped passengers food, water and restrooms after two hours, writes Secretary Ray LaHood here.

Air traffic controllers or security could keep passengers on planes longer, and overseas flights get to set their own rules. with exceptions allowed only for safety or security or if air traffic control advises the pilot in command that returning to the terminal would disrupt airport operations.

"This rule was adopted in response to a series of incidents in which passengers were stranded on the ground aboard aircraft for lengthy periods and also in response to the high incidence of flight delays and other consumer problems. In one of the most recent tarmac delay incidents, the Department fined Continental Airlines, ExpressJet Airlines and Mesaba Airlines a total of $175,000 for their roles in a nearly six-hour ground delay at Rochester, MN."

Airlines also have to reschedule "chronically delayed flights," post delay information online, and boost charges on pre-sold tickets. "The rule may be obtained on the Internet at www.regulations.gov, docket DOT-OST-2007-0022."

Updated: LaHood told me through a spokesman that his rule "goes above and beyond legislative proposals."  No immediate comment on that from the Radnor-based FlyersRights.org, which has been agitating for Congress to require shorter forced waits.