WASHINGTON — More flights on U.S. airlines are running late or getting canceled, and complaints are rising.The Transportation Department said Wednesday that 76.9 percent of flights arrived on time in May, down from 79.6 percent in April and 79.4 percent in May 2013.Hawaiian Airlines and Alaska Airlines, which get good weather on many routes, rank best. ExpressJet and Envoy, which fly smaller planes for big airlines, rank last.The government says the largest airlines canceled 1.9 percent of their U.S. flights in May, nearly double the rate in April and last May.The airline industry said bad weather was largely to blame. Jean Medina, a spokeswoman for the trade group Airlines for America, said that nearly 8,300 flights were canceled due to storms in the Midwest and Northeast between May 8 and May 16, accounting for more than half of the month's cancellations.Four domestic flights — all on United — and one international flight operated for United by ExpressJet were stuck on the ground longer than federal rules allow. A United spokeswoman said the airline was cooperating with federal officials investigating the incidents.Fliers filed 1,010 complaints with the government against U.S. airlines in May, up from 720 a year earlier. About half involved flight problems such as delays and cancellations.