During the month of May 5 planes were stuck on the tarmac for three hours or more. May was the first month under a new rule banning lengthy tarmac delays.

In May 2009 there were 35 three-hour delays, so the decrease is significant. United Airlines operated four of the five flights this May. One of those four stayed on the tarmac for nearly five hours.  All of the United flights were bound for Denver on May 26 when serious thunderstorms and hail moved through Colorado. 

Denver International Airport had delays up to 60 minutes on that day as well as limited use of runways. The fifth was a Delta Air Lines Flight from Atlanta to Dallas-Fort Worth on May 28, a day when thunderstorms arose in Dallas.

Bad weather and thunderstorms are one of the main causes of flight delays because they are difficult for airlines and airport officials to predict.
The Department of Transportation said it will be weeks or months before fines are issued against the airlines for violations.

The maximum fine is a heavy $27,500 per passenger for airlines that do not return their planes to the terminal within the allotted three hours.

Source: The Associated Press