Before airline deregulation in 1978, Rule 240 was literally a federal requirement. Nowadays, it's a term describing what individual airlines will do for late or stranded passengers. In fact, the major airlines have filed "conditions of carriage" with the U.S. Department of Transporatation (DOT) guaranteeing their respective Rule 240s.

If your flight is delayed or cancelled, or if you've missed your flight connection, these policies may give you free meal vouchers, hotel accommodations, phone calls, and other amenities. You may be booked on a substitute flight -- even on another airline -- and you may be compensated or given a full refund if the flight problems persist.

How can you use Rule 240 to protect your rights?

Always carry a printed copy of your airline's Rule 240. Though the DOT requires airlines to keep a Rule 240 copy available for passengers at every ticket counter, don't count on that.

(Click on your airline's name below for a copy of its official Rule 240.)

Read Rule 240 carefully before you use it. Many airline ticket agents do not know these policies, so you should be the expert

For example, Rule 240s generally apply only to delays that are absolutely the airline's fault, such as mechanical delays. They do not apply to such events as: weather, strikes, "acts of God," or other occurrences that the airlines say they cannot control.

Be polite but very firm about your rights under Rule 240. You'll win most battles at ticket counters when you say the phrase "Rule 240" and show the agent your printed copy of the airline's policies. However, don't hesitate to keep going up the chain to supervisors if you're not satisfied. Sometimes, airlines will even go beyond Rule 240 requirements in the name of customer service.