Yes, we’ve repeatedly made fun of delusional Spirit Airlines CEO Ben Baldanza for his claim that his company is the “most consumer-friendly” airline around, especially when it comes in dead-last in traveler opinion surveys and is the only U.S. carrier to make a recent list of the world’s worst airlines. And a new study confirms that Spirit’s passengers are several times more likely to complain than passengers on any other domestic carrier.

Just check out the graph above, culled from the new U.S. Public Interest Research Group study [PDF] on airline complaints filed with the Dept. of Transportation.

Between 2009 and 2013, Spirit was not only the airline with the highest rate of complaints to the DOT, but its rate was anywhere from three to nine times worse than any of its competition. Additionally, while many of the airlines in the study — with a couple notable execption — demonstrated no substantial growth in complaints during this five-year period, Spirit’s complaint rate rose by more than 20%.

“As the airline has grown in the past several years, complaints against [Spirit] have skyrocketed,” reads the report. “Since 2008, the DOT has hit Spirit with five different fines totaling $565,000 for violating various consumer protection laws concerning oversales, baggage, and multiple cases of deceptive advertising.”

Spirit’s numbers are so much higher than the complaint rates for the competition that U.S. PIRG had to include a second graph that omits Spirit just to present more precise information about the rest of the industry:

Aside from Spirit, the most noticeable data on the graph belongs to United, which saw a massive spike in 2012 following its merger with Continental. Of course, complaints had been on the rise at the airline before the acquisition and still remain higher than almost all other carriers.

Speaking of mergers, as US Airways and American finish combining everything, it will be interesting to see how consumers react. American had been on the rise during the years leading up to its marriage to US Airways, while that carrier’s complaint rate had been trending downward. Granted, AA was going through bankruptcy and was having a lot of trouble with cancelled and delayed flights during that time.

Frontier Airlines may not be a household name to casual travelers, but it has grown in recent years in an effort to link people in underserved regions of the country to major airline hubs. But US PIRG points out that this growth has resulted in growing pains, with Frontier leaping from the middle of the pack to become second only to Spirit in the complaint rate department.

“When airlines cut corners, it causes all sorts of headaches for passengers,” said Laura Murray, U.S. PIRG Education Fund Consumer Associate. “These complaints show that the airlines and policymakers should act to improve service.”

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