Domestic airlines in February were more on time than a year ago, according to data released Thursday by the U.S. Department of Transportation.

And the Transportation Department said it received about 15,000 complaints about United Airlines, which refused to honor mistakenly low fares that savvy consumers tried to book through the carrier’s Denmark website on Feb. 11.

The Transportation Department said United did not have to honor the fares, partly because those consumers lied about where they lived, claiming billing addresses in Denmark to game the system and trigger the erroneous fares.

Meanwhile, far more than usual excessive tarmac delays were reported for February. Of the 24 excessive delays, nine were because of a Feb. 27 snowstorm in Texas.

Overall, airlines arrived on time 72.8 percent of the time in February, up from 70.7 percent in February 2014.

The most on-time airlines were Alaska Airlines, 85.1 percent; Hawaiian Airlines, 82.2 percent; and Delta Air Lines, 78 percent.

Worst were American Airlines’ regional jet service Envoy Air, 53.3 percent; Frontier Airlines, 58.8 percent; and JetBlue Airways, 59.7 percent.

Southwest, which last year struggled to be on time, continued to show improvement, ranking fourth overall at 77.5 percent. United and American were slightly above average at around 73 percent.

At Chicago O’Hare International Airport, just 57.7 percent of departures were on time. Only LaGuardia was worse, at 56.5 percent among large U.S. airports.

In February, the Transportation Department received 1,362 complaints about airline service from consumers, up 16 percent from February 2014.

Ultra-discount airlines Frontier and Spirit, known for bare-bones fares and numerous add-on fees, garnered by far the most complaints.

The average in February was about two official complaints per 100,000 passengers. Frontier had 14 and Spirit about nine per 100,000.

The 15,000 complaints about United’s mistaken fare were counted as consumer “opinions.”

United’s website for Denmark travelers offered first-class transatlantic tickets from England for as little as $51, among other super-cheap fares.

The Transportation Department did not require United to honor the mistaken fares, in part because the fares, listed in Danish krone, appeared on a website not marketed to U.S. customers.

It noted customers “had to manipulate the search process on the website in order to force the conversion error to Danish krone by misrepresenting their billing address country as Denmark when, in fact, Denmark was not their billing address country.”

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