WASHINGTON (AP) - Airline passengers are getting grumpier, and it's little wonder.
Airlines keep shrinking the size of seats to stuff more people onto planes, those empty middle seats that once provided a little more room are now occupied and more people with tickets are being turned away because flights are overbooked.
Private researchers who analyzed federal data on airline performance also said in a report being released Monday that consumer complaints to the Department of Transportation surged by one-fifth last year even though other measures such as on-time arrivals and mishandled baggage show airlines are doing a better job.
"The way airlines have taken 130-seat airplanes and expanded them to 150 seats to squeeze out more revenue I think is finally catching up with them," said Dean Headley, a business professor at Wichita State University.
"People are saying, "Look, I don't fit here. Do something about this.' At some point airlines can't keep shrinking seats to put more people into the same tube," he said.
The industry is even looking at ways to make today's smaller-than-a-broom closet toilets more compact in the hope of squeezing a few more seats onto planes.
"I can't imagine the uproar that making toilets smaller might generate," Headley said.
In recent years, some airlines have shifted to larger planes that can carry more people, but that hasn't been enough to make up for an overall reduction in flights.
The rate at which passengers with tickets were denied seats because planes were full rose to 0.97 denials per 10,000 passengers last year, compared with 0.78 in 2011.
It used to be in cases of overbookings that airlines usually could find a passenger who would volunteer to give up a seat in exchange for cash, a free ticket or some other compensation with the expectation of catching another flight later that day or the next morning. Not anymore.
Regional carrier SkyWest had the highest involuntary denied boardings rate last year, 2.32 per 10,000 passengers.
United Airlines had the highest consumer complaint rate of the 14 airlines included in the report, with 4.24 complaints per 100,000 passengers. That was nearly double the airline's complaint rate the previous year. Southwest had the lowest rate, at 0.25.
At the same time complaints were increasing, airlines were doing a better job of getting passengers to their destinations on time.
The industry average for on-time arrival rate was 81.8 percent of flights, compared with 80 percent in 2011. Hawaiian Airlines had the best on-time performance record, 93.4 percent in 2012. ExpressJet and American Airlines had the worst records with only 76.9 percent of their planes arriving on time last year.
The industry's shift to charging for fees for extra bags, or sometimes charging fees for any bags, has significantly reduced the rate of lost or mishandled bags. Passengers are checking fewer bags than before, and carrying more bags onto planes when permitted.