While airlines might not be leaping at the chance to tell customers how to file complaints about their service, that hasn’t stopped more travelers from sharing their tales of woe with the Department of Transportation. In fact, the number of complaints filed by beleaguered passengers increased by nearly 30% last year. 

That figure comes from the Department of Transportation’s recently released Air Travel Consumer Report [PDF] that found the DOT’s Aviation Consumer Protection Division received 20,170 complaints from consumers in 2015, representing a 29.8% increase from the 15,539 complaints received in 2014.

According to the DOT, the complaints cover a wide range of issues including flight problems, baggage, reservation and ticketing, refunds, customer service, disability, and discrimination.

American Airlines received the most complaints across many of the DOT’s categories: 1,094 for flight problems, 152 for oversales, 506 for reservations, 479 for fares, 415 for refunds, 601 for baggage, 426 for customer service, and 183 for disability issues.

While the number of complaints filed against American outpaced other airlines, Spirit Airlines had the highest rate of complaints at 10.97 complaints for every 100,000 passengers. In all the airline collected 2,069 complaints.

The next closest complaint rate was for Frontier Airlines, which saw 5.09 complaints for every 100,000 passengers.

The DOT’s report also highlights other performance data for airlines including on-time performance, cancellations, delays, and mishandled baggage.

When it came to on-time performance, carriers posted a rate of 79.9% for the entire year, up from 76.2% in 2014.

The airlines with the highest on-time rates were Hawaiian Airlines, Alaska Airlines, and Delta Air Lines. Those with the lowest rates were Spirit, JetBlue Airways, and Virgin America.

In 2015, carriers canceled 1.5% of their scheduled domestic flights, the DOT reports, representing an improvement from the 2.2% of flights canceled in 2014.

Envoy Air, ExpressJet Airlines, and SkyWest Airlines had the highest rate of canceled flights, while Hawaiian Airlines, Alaska Airlines, and Delta Air Lines had the lowest rate.

In 2015, there were 61 domestic flights with tarmac delays longer than three hours and 15 international flights with tarmac delays longer than four hours at U.S. airports. Each of these reported extended tarmac delays were investigated by the Department.

But despite the sometimes long delays for airlines, the DOT report found that airlines lost slightly fewer bags in 2015.

Carriers posted a mishandled baggage rate of 3.24% per 1,000 customers, down from the 2014 rate of 3.61%.

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