Complaints about airlines in April were 300% higher than in 2019

If you had a complaint about an airline in April, you were not alone.

New data out Thursday from the U.S. Department of Transportation show that complaints about airlines increased about 15% from March — and were up 321.5% from those received in April 2019.

In all, 5,079 complaints about airlines were received in April. That's up from 4,423 in March and 1,205 in April 2019. Of those complaints, 62.5% were against U.S. carriers, while 27.7% were against foreign carriers, and 9.8% were against travel companies.

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A plurality of complaints — 32.3% — were about refunds. Next was flight problems, such as delays and cancelations, which accounted for 30.5% of the complaints.

Rounding out the top five list were complaints about reservations/ticketing (9.8%), baggage issues (8.7%) and fares (8.1%).

Refunds are often a top category because the DOT has significant power to compel airlines to issue them. Last year, DOT fined Air Canada $2 million for not properly refunding customers, ending an ongoing dispute between the airline and some customers that began during the earliest stages of the pandemic.

The spike in passenger unhappiness comes ahead of what's shaping up to be a rough summer for air travel. The airline industry has endured a particularly poor stretch operational reliability, and the system remains wobbly as demand soars and carriers try to ramp up operations since the depths of the pandemic. It all suggests that flight problem complaints could rise even further in future DOT reports, known as the Air Travel Consumer Report.

As for the cause, airlines are largely blaming the Federal Aviation Administration for air-traffic control staffing issues, while the federal government believes airlines are trying to operate unsustainable schedules. Because of a data reporting lag, it will be a few months before complaints resulting from recent issues will be reported out.

Related: Why do flight cancellations and delays keep happening?

Regardless of the reason, consumers often have a lot to lose during irregular operations. It can sometimes take days for airlines to recover — especially as flights are full and rebooking options are few. The Biden administration's Transportation Department has prioritized consumer protection — and is encouraging passengers to file reports with them.