Delayed and canceled flights were the top frustrations for air travelers in the past five years, and more of them complained about Spirit Airlines than any other carrier, a Washington-based advocacy group reported last week.

U.S. PIRG analyzed U.S. Department of Transportation data to conclude that Spirit had at least three times more complaints per 100,000 passengers than any other airline. Most complaints were related to flight problems, rather than expensive water, baggage fees or other costs.

Spirit said consumers often file complaints because they "do not fully understanding that we offer unbundled fares that let them control how much they spend," said Maggie Espin-Christina, a spokeswoman for the Miramar, Fla.-based airline.

But the company said it will put a greater focus on keeping travelers happy. Espin-Christina said 2014 is Spirit's "Year of the Customer" and it is "working every day to reduce complaints by helping customers learn about how to fly Spirit to go where they want and keep more money in their pocket."

Spirit Airlines, which began operating in the Twin Cities in 2012, is known for keeping base fares low while charging for "extras" like baggage, water at $3 a bottle and $10 for airport agents to print a boarding pass. In the past year Spirit announced it would fly from MSP to more cities, including Los Angeles, Detroit, Houston and Tampa.

Laura Murray, the author of the U.S. PIRG report, said it's discouraging that Spirit is "quick to blame the consumer."

"If that's the obvious pattern, then they are not being upfront," Murray said in an interview.

Murray examined five years of airline passenger complaint data to DOT and was surprised to see that Spirit was "so far above the pack" in complaints. Other airlines averaged about one complaint per 100,000 travelers.

Despite Spirit's above average complaints, Espin-Christina said, "while we want every customer to have a great experience, eight complaints per 100,000 enplanements is a pretty small number."

According to the report, the Department of Transportation has fined Spirit five times since 2008, totaling $565,000, for violating various consumer protection laws including over sales, baggage, and multiple cases of deceptive advertising.

The dominant carrier in the Twin Cities, Atlanta-based Delta Air Lines, has improved its standing from second in passenger complaints to 11th last year. The majority of complaints, like Spirit, were about flight problems.

Emily Herke of Farmington said her honeymoon cost her an extra $957 because of flight problems on Delta.

Herke and her husband took a Delta flight to Miami to go on a Carnival cruise for their honeymoon. But two faulty planes and a five-hour delay caused them to have to board the ship in a different city.

Herke said she complained to Delta and received a $100 Delta voucher and $150 in gift cards, but she still was "not pleased at all with the service we received or the way Delta tried to make up for their mistakes."

Murray also recommends that passengers complain to the Department of Transportation. Murray said consumers like Herke justifiably expect that flights will be on time, and that they will be "treated like people and not cattle."

Passengers can contact U.S. DOT at dot.gov/consumer or 202-366-2220.