If you're unhappy about the state of air travel in the U.S.,Michael Schmidt you're in good company.

Complaints about U.S. airlines climbed sharply in the first half of the year, consumer advocates say, as passengers remain deeply dissatisfied despite some improvements in performance.

"The complaint data is pretty jaw-dropping," said Teresa Murray, a consumer advocate with U.S. Public Interest Research Group, which published a new report based on data released by the Department of Transportation.

Flight cancellations were down significantly in the first nine months of the year, according to the DOT. Murray called that trend encouraging but said delays and mishandled luggage remain major problems.

"People are still ticked off and unhappy with their airline experience," she said in an interview. "The complaints are continuing to pour in."

Travelers filed more than 26,000 formal complaints about U.S. airlines in the first five months of 2023 — more than double the number filed during the same period last year, according to the report, and on pace to break the annual record set in 2022.

The aviation system has struggled to keep pace with a surge in demand, as travel volumes rebounded quickly to pre-pandemic levels. That's left both the airlines and many air traffic control centers short-staffed.

"We are seeing more people flying than ever with fewer cancellations than we have seen in years," Transportation Secretary Pete Buttigieg said at a news conference last month.

The biggest U.S. airlines canceled about 1.6% of flights from January through September of this year — down from 2.8% during the same period last year.

Buttigieg called that "a clear improvement in the numbers" and said airlines deserve some of the credit, "both in terms of the realism of their schedules and in terms of having the staffing and the preparation to meet the demand that's come in."

But at the same time, the number of delays has grown.

The largest U.S. airlines had an on-time performance of 76.2% during the first nine months of the year, down from 76.6% last year. That figure has fallen below 77% only one other time in the past 15 years, Murray said.

The aviation system was largely able to avoid major service disruptions during the recent Thanksgiving holiday. But many travelers haven't forgotten the meltdown of 2022, when winter storms and a software glitch at Southwest Airlines caused thousands of canceled flights and chaos across the country.

Murray said travelers should brace for another challenging holiday travel season.

"We know that the flights are going to be absolutely jam-packed here in the next couple of weeks," she said. "We definitely recommend that you do the old thing of getting to airports early because you have less of a chance of getting bumped. You have more of a chance of getting where you want to get."