Despite some severe winter weather, U.S. airlines managed to operate 72% of their domestic flights on time in December, unchanged from the same month a year before. And they managed to do so with no significant long tarmac delays.

Flight cancellations, however, spiked to 3.7%, as the carriers canceled 19,692 operations during the month. That’s up from a cancellation rate of 0.7% for November 2010 and 2.8% for December 2009.

The data, from the Transportation Department’s latest monthly airline report card, could add fuel to the debate over the merits of the department’s rule limiting tarmac delays to three hours.

Critics of the rule say it leads to a higher level of cancellations, particularly during weather alerts, and ends up creating more inconvenience for passengers.

Supporters of the rule say it has ended the specter of long “hostage” situations when carriers are forced to wait out a storm. After the rule became effective in April, such incidents declined to zero in the summer and fall.

In December there were three incidents that exceeded the three-hour mark, but they missed by only 12 minutes or less. Two were departures from Detroit on Dec. 12 (Delta to Miami and Pinnacle to Cedar Rapids, Iowa), and one was a diverted United flight from San Diego to San Francisco on Dec. 27.

There were also 317 tarmac delays of two hours or less in December, up from 105 in November.

The DOT data for on-time performance and cancellations indicate that among the major carriers, JetBlue had a particularly challenging month. The carrier turned in one of the lowest on-time rates in recent memory, with only 58.6% of its flights arriving within 15 minutes of schedule. It also experienced the highest cancellation rate of any carrier, scratching 1,542 departures, or 8.5% of its scheduled flights.

Delta was the only other major airline with a cancellation rate exceeding the month’s 3.7% average, with a rate of 4.7%.

On a positive note, the DOT’s data on oversales indicate that carriers improved their handling of denied-boarding situations in the fourth quarter and the year.

For the quarter, the carriers reduced the incidence of involuntary bumping to 0.79 per 10,000 passengers, down from 1.13 a year earlier. For the calendar year, the denied boarding rate fell to 1.09 per 10,000 passengers from 1.23 in 2009.

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