Just three flights waited three or more hours on airport tarmacs in June, according to the Transportation Department, compared to 268 flights in the same month last year. June marked the second full month since federal regulators instituted fines of up to $27,500 for each passenger involved in a delay of three-plus hours. The cancellation rate remained unchanged at 1.5%, despite fears that the rule would force widespread cancellations in order to avoid the stiff fines. But the Air Transport Association said results should not be judged by a single month's cancellation figures. "Flight delays and cancellations vary significantly from month to month as a result of variables, including weather and airspace congestion," a spokeswoman noted.