The U.S. Department of Transportation rejected requests by five carriers for exemptions to new tarmac delay rules set to take effect April 29.

American Airlines, Delta Air Lines and JetBlue Airways requested exemptions at New York JFK; Continental requested exemptions for Newark and New York LaGuardia; and US Airways requested an exemption for Philadelphia. The new rules"prohibit" U.S. airlines from keeping domestic passengers on airport tarmacs for more than three hours without an opportunity to deplane. "This is an important consumer protection, and we believe it should take effect as planned," according to a statement by DOT Secretary Ray LaHood.