NEW YORK (AP) -- Denver-area thunderstorms appear to be to blame for the majority of three-hour or longer tarmac delays in May, the first month under a new rule banning lengthy waits on grounded planes.

The government says five flights were stuck on the tarmac for three hours or more in May. Four of them were United Airlines flights headed for Denver on May 26, when severe thunderstorms and hail swept through Colorado.

The fifth was a Delta Airlines flight headed for Dallas-Fort Worth on May 28, a stormy day for the area.

The five flights are a steep drop off from May 2009, when there were 35 three-hour delays.

The Department of Transportation says it will be weeks or months before any fines may be levied against airlines for violations.

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