Policies differ on how long you might be sitting

— -- Continental cal, American amr, JetBluejblu and Virgin America have limits in their published policies on how long they'll let delayed flights sit on tarmacs before returning to the gate. But they allow wiggle room if planes are expected to take off shortly after the limit is reached. The reasoning: Although some passengers on a delayed plane might want to return to the terminal, others may want to get to their destinations as quickly as possible. Returning to the terminal means a longer delay and could result in the flight being canceled. Customers who still must travel would then be competing for what could be few seats on later flights.

Regional airlines flying under major carriers' names are responsible for their own operations because they have their own operating certificates, issued by the Federal Aviation Administration. However, regional carriers typically are obligated to meet the same customer service standards. All major U.S. airlines have policies, usually posted on their websites, that state what they do for passengers aboard delayed planes. They generally follow guidelines established by their trade group, the Air Transport Association, which say airlines "will make every reasonable effort to provide food, water, restroom facilities and access to medical treatment."

The caveat: safety. Additional water, food and toilet servicing won't be delivered, the plane won't be allowed to return to the terminal, and passengers won't be allowed to get off if weather or limitations at the airport make it dangerous.

JetBlue has a schedule of compensation and gives vouchers for future travel to passengers delayed for reasons under its control. Most other carriers offer travel vouchers as compensation for delays that are under their control, but have no formal schedule of compensation. Airlines typically don't compensate passengers delayed on the ground because of weather or air-traffic congestion. Here's a summary of policies of the USA's largest carriers.

•AirTran.aai Doesn't have a time limit for how long a plane will be delayed on the ground before returning to the terminal. However, boarding won't begin if local managers, dispatchers and pilots know the plane will be delayed at the gate for two or more hours. For shorter known delays, boarding won't begin until an hour before the expected departure time.

•American. Planes delayed more than four hours will return to the terminal and passengers can choose to get off, if it can be done safely. On flights of its American Eagle regional partner, the limit is three hours. In some cases, this could mean canceling the flight.

•Continental. Planes delayed more than three hours will return to the terminal, and passengers can choose to get off, if it can be done safely. In some cases, this could mean cancellation of the flight.

•Delta.dal Has no specific time limit. After a two-hour ground delay, however, managers and the pilot estimate the time remaining to take off and assess conditions onboard and the weather. They determine whether the plane will continue waiting or return to the terminal, if weather and the situation inside the airport allow it.

•JetBlue. After five hours on the ground, passengers wishing to get off will be allowed to do so at the terminal, or if necessary by other means, if it can be done safely.

•Northwest. Its policy is similar to Delta's. Delta acquired Northwest in 2008, and the Northwest operation is being gradually absorbed into Delta.

•Southwest.luv Doesn't have a limit for lengthy ground delays. Boarding doesn't begin if local managers, dispatchers and pilots know the plane will be delayed at the gate for two or more hours. For shorter known delays, boarding won't begin until 30 minutes before the expected departure time.

•United.uaua Doesn't have a limit. The company's commitment, posted on its website, is to "manage the situation aggressively to minimize delays of greater than three hours, and make every reasonable effort to prevent" delays of more than four hours.

•US Airways.lcc No time limit has been set. But the company's customer service commitment says that its policy includes "time frames in which services and facilities will be made available during a long on-aircraft delay."

•Virgin America. After two hours delay on the ground, the pilot, lead flight attendant and dispatcher confer every 30 minutes about conditions onboard and how long the delay is expected to last. They can decide to return to the terminal if conditions warrant. After four hours, the pilot is directed to begin organizing an attempt to return the plane to the terminal, if weather conditions and conditions at the airport allow it to be done safely.