NEW YORK — It’s official: This winter was the worst for fliers in the 20 years that the government has collected data.During the first three months of the year, U.S. airlines canceled 4.6 percent of their flights, the Transportation Department announced Tuesday. The worst winter before that was 2001, when 4.4 percent of flights were scrapped. Mother Nature is mostly to blame, with a relentless wave of snow and ice storms paralyzing airline traffic nationwide. But operations did improve in March as U.S. airlines posted an on-time arrival rate of 77.6 percent, compared with 70.7 percent in February.Carriers also reported no tarmac delays of more than three hours on a domestic flight, according to the Bureau of Transportation Statistics’ monthly report. One British Airways flight from Houston to London was delayed on the tarmac for more than four hours.Hawaiian Airlines was the top performer, with 91.6 percent of its flights arriving on time, while ExpressJet Airlines fared the worst, with only 70.9 percent of flights arriving on time.Fort Worth-based American Airlines ranked fifth, at 80.5 percent. Southwest Airlines had the second-worst performance, at 72.9 percent.Airlines also lost more luggage in March, reporting a mishandled-bag rate of 3.68 per 1,000 passengers, up from 3.03 in March 2013.Carriers are quicker to cancel flights these days, sometimes a day before a storm. The shift in strategy came in response to new government regulations and improvements to overall operations. Canceling quickly also reduces expenses. In May 2010, a Transportation Department rule took effect prohibiting airlines from keeping passengers on the tarmac for three hours or more. So airlines now cancel blocks of flights to avoid potential fines of up to $27,500 per passenger, or $4.1 million for a typical plane holding 150 fliers. Making things worse for travelers, airlines are cutting unprofitable flights and packing more passengers into planes. When flights are canceled, the stranded passengers have nowhere to go. Some end up waiting days for another flight. In March, JetBlue had the highest cancellation rate among the bigger airlines: 2 percent of flights. That was closely followed by the merged American-US Airways, at 1.9 percent. Southwest and United Airlines both canceled 1.1 percent and Delta Air Lines 0.2 percent. Some of the highest cancellation numbers came from smaller regional airlines operated by other companies on behalf of the major airlines. ExpressJet, which flies regional planes for American, Delta and United, scrapped 5.1 percent of its March flights.American Eagle canceled 4.1 percent of its flights, and SkyWest — another subcontractor — nixed 2.3 percent. Staff writer Andrea Ahles contributed to this report, which includes material from The Associated Press.