The nation's leading airlines have sharply improved their latest on-time ratings.

The Transportation Department said Thursday that 86.5 percent of flights on the leading carriers arrived on time in September.

That was the fourth best month in the 21 years of comparable records, and it was higher than the 80.3 percent on-time rating in August and 81.1 percent in September 2014.

Delta Air Lines, Alaska Airlines and Southwest Airlines had the best ratings; all were better than 87 percent. Spirit Airlines, at 76.7 percent, and JetBlue Airways, at 80 percent, had the worst marks. Hawaiian Airlines, typically among the most punctual, tumbled to 11th among the 13 airlines tracked. Smaller carriers including Allegiant Air and many regional airlines are not included in the numbers.

Consumer complaints to the government were rare but increased 70 percent from a year earlier. There were 1,351 complaints against U.S. airlines - a tiny fraction of the 55.8 million passengers who boarded one of the leading 13 carriers during the month.

ExpressJet, Alaska and Southwest had the lowest complaint rates, while budget airlines Spirit and Frontier continued to have the highest rates. Spirit passengers were 29 times more likely to complain than those on ExpressJet.