WASHINGTON — US airlines are struggling to stay on schedule, with nearly one in four flights arriving late.

The Transportation Department said yesterday that April’s on-time rating was worse than April 2012’s and below the 18-year average for the month. The airlines blamed much of the increase on bad weather.

The worst on-time rating was turned in by American Eagle. A computer-system crash on April 16 caused American Airlines and American Eagle to cancel many flights, and hundreds of others were late.

Hawaiian, Alaska and Delta were the top three airlines in on-time arrivals, each over 85 percent.

Among the busiest 29 US airports, passengers were most likely to be delayed on their way to Newark — wit only 65.6 percent of flights arriving there on time.

Two US flights were delayed on the tarmac for at least three hours, which could expose the carriers to fines from the Transportation Department. One was an April 19 Delta flight that sat on the tarmac at La Guardia for 183 minutes.

The airlines said that 34.3 percent of delays were caused by bad weather, up from 28.5 percent in April 2012. They said that only 5.3 percent of delays were due to factors within their control, such as maintenance problems or crew shortages.