There were more long delays in July on airport tarmacs than in the previous eight months combined.
In August one international flight was stuck for more than four hours. On Aug. 15, a Caribbean Airlines flight sat on the tarmac at New York's JFK Airport for four hours and 28 minutes before it took off for its destination, Trinidad and Tobago.
U.S. airlines are subject to huge fines if they keep passengers on a grounded plane for more than three hours. Violations start at four hours for international carriers at U.S. airports.
Almost four in five flights were considered on-time in August, meaning they arrived within 15 minutes of their posted schedule. At a rate of 79.2 percent, U.S. airlines were just slightly less on-time than a year earlier but better than July's 76 percent on-time rate.
Hawaiian and Alaska Airlines held their traditional top spots in the rankings. Delta was the most efficient major network airline, with an on-time rate of 83.9 percent. United was the worst.
Cancellations fell from both the month and year before. Fewer travelers complained about lost or damaged bags in August as well.
At the end of August, there were 56 flights that were chronically delayed—30 minutes late more than half the time—for two straight months. Flights were mostly operated by regional carriers doing business for bigger airlines. Many of them were departing from congested airports like Newark Liberty in the New York area or San Francisco International. No flights were chronically delayed for three consecutive months or more.