Denver-based Frontier Airlines has hit more turbulence for troubles that, despite relatively low fares, have shaken relations with travelers.

A new analysis of the nation’s 10 major airlines ranked Frontier last, citing high rates of “bumping” passengers involuntarily off flights, customer complaints, and fees for bags and changed flights. This seventh-annual report found that all airlines deteriorated in their performance with overall complaints increasing in 2022 by 87%. But Frontier’s reported data from 2022 showed that company gate agents denied boarding for more than 6,000 passengers against their wishes, an average of more than 16 every day and roughly 1 out of every 3,752 travelers, according to the report by “The Points Guy,” a travel information website. And Frontier led also in the rate of complaints with 22.6 for every 100,000 travelers in 2022 — more than twice the number of complaints reported by Spirit, the second-to-last carrier in that category.

Atlanta-based Delta Airlines fared best for the fifth year in a row in this multi-factor analysis.

Frontier’s descent in the rankings reflects frequent friction between the company and fliers in recent years that have prompted Colorado authorities to demand a federal investigation.

On Sunday, a woman who boarded a Frontier flight from Denver to Tampa “became belligerent” and was ushered off the plane. She hit a Frontier flight attendant with an intercom handset, according to a Frontier statement about that incident, and was arrested by Denver police. The police cited her for assault, then helped her find another flight to Tampa.

Frontier offers relatively low base fares but no longer makes agents available by phone in a booking process that seeks fees for services, and sometimes at airports travelers must agree to pay a fee to talk with a check-in counter agent. Online “chatbots” automated responses to common questions and “live chat” online messaging allow a form of interaction. And baggage size limits increasingly are enforced with gate agents paid a $10 bonus for every boarding passenger they catch with a bag that fails to fit into a measuring box set up at gates. Fliers caught with oversize bags must pay $99 penalties to be allowed to board. Customers in recent weeks have chafed at this practice, complaining they were charged unfairly.

Frontier officials declined to comment on the rankings or to discuss friction with fliers.

However, Frontier spokeswoman Jennifer de la Cruz acknowledged, in emailed statements, “a commission for gate agents” who catch fliers who try to board planes with oversize bags. “We have on a number of occasions investigated specific claims by customers who say they were unfairly charged for a bag at the gate and typically find there is more to the story. All complaints are taken seriously and consumers are encouraged to contact our Customer Care Team with any concerns,” de la Cruz said, referring to Frontier’s online options.

The $10 commission “is simply designed to incentivize our team members to ensure compliance with the bag size requirements to ensure all customers are treated fairly, including the majority who comply with the rules,” she said.

Do fliers always have to pay to speak with a Frontier employee at the ticket counter? “It depends,” de la Cruz said via email. “If it is something they can easily do themselves on their phone/online, then, yes, there is an agent assist fee. If it is not something they can easily do on their own, there is no charge.”

Is Frontier reconsidering whether to restore direct human contact in-person or by phone rather than rely on the online “chatbot” and “live chat” options? “We do not have plans at this time to move away from chat versus voice calls.”

In Colorado, no other airline has racked up complaints as frequently as Frontier, which had a rate of more than 600 complaints in 2020, according to Colorado Attorney General Phil Weiser. In August, Weiser called on the U.S. Department of Transportation to investigate Frontier. Weiser also led a coalition of attorneys general from 38 states (including California, New York, Pennsylvania, Massachusetts, Michigan, North Carolina, Ohio and Virginia) pushing federal airline industry regulators to address flier woes.

Weiser contends air travelers booking tickets “should enjoy a reasonable expectation of being treated fairly, respectfully, and consistently by airlines.”

He and fellow state attorneys, in a letter to Congress, said that, while federal law places the central responsibility for protecting airline customers on federal transportation officials, little has been done to hold airlines accountable amid rising complaints. State attorneys argued that they are well-positioned to protect consumers — if Congress would authorize them to do so.

When a Frontier flight from San Diego to Denver this week was delayed due to a mechanical failure, gate agents gave passengers a choice to re-book on next-available Frontier flights that would require overnight stays in connecting airports at fliers’ expense. Then after five hours of delay due to the mechanical breakdown – apparently due to a faulty fire detector in a cargo hold, a crew member said — the plane was cleared for take-off. But agents refused to allow passengers who had rebooked onto lengthier fights the next day to re-board the flight to Denver, even though their seats still were available.

Gate agents threatened to call the police when one angry passenger yelled.

The pilot then intervened, telling gate agents he was going to override their refusal. On his phone, he reached a live “passenger planning” official who approved a re-boarding of passengers denied access, including a Colorado Springs couple with a 6-month-old child.

On the flight, passenger Rachel Bliss of Highlands Ranch, a boiler company sales engineer and mother of three children, lamented difficulties seeking refunds for her children’s tickets after a Frontier flight cancellation. And at the gate before the Denver flight, Bliss said, she’d faced paying the $99 fee to board when her daypack measured too big — until she “collaborated” with another passenger to avert the penalty by off-loading some of her items into the other passenger’s bag.

After witnessing fliers’ rancor and wrangling over five hours of uncertain waiting in San Diego, Bliss shook her head upon landing on the tarmac back in Denver.

“Maybe we should form a Frontier Airlines flyer support group,” she said. “I really do feel trauma-bonded with these people who went through so much.”

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