When United and Continental decided to become a couple, they weren’t just combining their bank accounts and airplane collections, they also had to combine all the complaints people file against them. But even that doesn’t account for the huge increase in consumer complaints filed against the united United.

Yesterday, the DOT released its latest Air Travel Consumer Report [PDF] — we’ve already covered some of the info from the report here — which includes a breakdown of consumer complaints by U.S. airline.

And according to these numbers, for the first half of 2012, United Airlines is responsible for 1,740 of 5,159 complaints filed between January and June. That’s an incredible 33.6% of all complaints. It’s almost more than three times the amount filed for runners-up American Airlines (552) and U.S. Airways (511). Delta, which lost the title of nation’s largest airline when United and Continental merged, was a distant fourth place in the complaint department with only 443.

Could United’s huge complaint number be merely a fact that its numbers are now combined with Continental’s?

Nope.

A look back at the report [PDF] for the same time period in 2011 found United with only 501 complaints — third behind Delta (702) and American (636) — while Continental had only racked up 381 complaints. Combined, these two airlines account for less than 20% of all consumer gripes filed with the DOT during those six months.

Looking back through the month-to-month breakdowns of complaints, you can see that the problem occurred back in March, when United and Continental merged their reservation systems — with more than a few problems.

And when you look at the breakdown of complaints by category, you see that reservations and ticketing is a huge problem for United.

Out of the 696 total complaints filed in this category so far in 2012, United was responsible for 296 (42.5%) of them. A year ago, the combined United and Continental reservations/ticketing complaints only accounted for 24.5% of complaints in that category.

Consumer issues with reservations logically spill over into complaints about refunds and customer service in general, both areas in which the new United saw a huge increase.

196 travelers complained about refund problems with the airline. That’s more than 45% of all complaints in the category. Compare that to a total of only 79 complaints for the same time period in 2011 for United and Continental.

Meanwhile, not only was United’s 330 customer service-related complaints by far the most for the first half of 2012 (approximately 42% of all complaints), United was the only airline with triple-digit numbers in this category.

United tells the Houston Chronicle that it’s aware of the unpleasant stats and wants to do better:

“Our operational performance is not where it should be, and we recognize its impact to our customers and employees,” United said in a statement when asked about the most recent statistics… We are taking immediate action to improve, including adding spare aircraft and more ground time between flights, and making changes to our technology to give employees and customers more reliability. So far in the month of August, we are seeing improved results.”

Only time will tell if these complaint stats improve as the happy couple sorts out their honeymoon issues. Delta experienced similar customer service nightmares when it merged with Northwest but has demonstrated improvement in recent airline surveys.

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