Passenger complaints can reveal a lot about the travel experience these days, from customer service to delays, hidden fees, overbooked flights, and accommodations for travelers with disabilities. While many people take to social media to share their gripes or reach out to an airline’s customer service team for answers, that doesn’t always resolve every issue. 

So, others may take their grievances one step further and file an official complaint with the U.S. Department of Transportation. In the first half of 2026, there were 29,000 individual complaints filed against U.S. airlines with the DOT. Knowing that some airlines fared better than others when it came to passenger satisfaction, we dug into the data from January to June 2026 to determine which U.S. airlines received the highest number of complaints per 100,000 passengers.

5. Delta Air Lines

Total consumer complaint cases: 4,534
Number of passengers: 75,065,902 
Complaints per 100,000 passengers: 6.04

Delta is one of the industry’s strongest performers for reliability, but that might say more about the overall state of air travel in the U.S. than about the airline itself. Despite only 80.9% of flights arriving as scheduled last year, it was the most on-time U.S. airline in 2025 according to DOT data. With its largest hub at Hartsfield-Jackson Atlanta International Airport, the world’s busiest airport, Delta operates more than 1,000 flights daily to 200 worldwide destinations. 

While it represents a small share of the total number of passengers Delta carried in the first half of 2026, the airline received over 1,000 complaints in the “flight problems” category, which encompasses “cancellations, delays, or any other deviations from schedule, whether planned or unplanned,” according to the DOT.

4. United Airlines

Total consumer complaint cases: 4,524
Number of passengers: 64,607,289 
Complaints per 100,000 passengers: 7.00

Billed as the world’s largest airline by available seat miles, United connects 175 million passengers per year to over 350 destinations across six continents. Its global expansion as of late has taken passengers to some unexpected destinations, such as Greenland, Mongolia, and Palau. While United customers have no shortage of options for where to fly to, the airline doesn’t always deliver on the customer experience front, according to DOT data. In the first half of 2026, the majority of official DOT complaints against United were related to refunds, flight problems, and baggage.

3. JetBlue

Total consumer complaint cases: 1,700
Number of passengers: 17,136,126
Complaints per 100,000 passengers: 9.92

Since its founding in 2000, New York City-based JetBlue has grown into one of the country’s largest low-cost carriers. It currently serves over 100 destinations across the Americas and Europe. The airline prides itself on offering a more premium flying experience than many rival low-cost carriers, which includes complimentary perks like free in-flight Wi-Fi and personal seatback entertainment. 

However, the airline has struggled when it comes to reliability, ranking near the bottom last year for on-time performance among major U.S. airlines. In the first half of 2026, JetBlue received the highest number of DOT complaints for flight-related problems such as cancellations or delays.

2. American Airlines

Total consumer complaint cases: 9,046
Number of passengers: 74,036,245 
Complaints per 100,000 passengers: 12.22

In terms of total numbers, American received the most consumer complaints from January to June 2026, reflecting the fact that it is one of the world’s largest airlines by fleet size and passengers carried, operating around 6,000 daily flights. American has its largest hub at Dallas Fort Worth International Airport, the fourth-busiest in the world. 

Interestingly, despite American carrying a similar number of travelers as Delta during the same period, it had more than double the number of complaints on a per-passenger basis. Of the 9,046 complaints filed against American with the DOT, over 2,700 were due to flight issues such as delays, and nearly 2,500 were due to failing to provide refunds in a timely manner.

1. Frontier Airlines

Total consumer complaint cases: 3,673
Number of passengers: 17,429,645 
Complaints per 100,000 passengers: 21.07

Based out of Denver, Colorado, Frontier Airlines is America’s largest ultra-low-cost carrier, currently serving around 120 destinations across North America, the Caribbean, and Central America. The airline operates on a model of advertising a very low base fare and charging for almost everything extra, from seat selection to beverages on board to printing a boarding pass at the airport. 

While the airline’s distinctive and artistic Plane Tails feature images of endangered species, aquatic, land, and sky animals — reflecting a mission to become America’s greenest airline — it also earned the dubious title of having the highest number of complaints per 100,000 passengers among U.S. airlines in the first half of 2026. The category with the highest total number of complaints for Frontier was for problems obtaining refunds for unused or lost tickets. 

Data note: The list above excludes Spirit Airlines’ complaint data since the carrier ceased operations in May 2025. Additionally, we omitted certain smaller carriers, such as Avelo and Breeze, which do not have passenger data available in the Air Travel Consumer Report.