The quality of airline service has got worse in 2014 because carriers continued to squeeze passengers in various ways.

The Airline Quality Rating (AQR), carried out by Wichita State University and Embry-Riddle Aeronautical University, has been evaluating the performance of airlines for more than 20 years. It was found that airline service suffered because airlines packed more people onto planes and landed less flight on time.

"As a group they generally did worse. We track four elements that we think are consumer relevant, on-time, baggage handling, complaints and things like that and literally all four of those got worse for the industry this year", said Dean Headley of Wichita State University.

Possibly, the most telling clue that how frustrated passengers have become is the number of complaints about airlines filed in 2014 with the Department of Transportation. The quality of Airline Quality Rating has been decreased to its lowest level since 2008.

According to AQR, on-time arrivals declined 2% and mishandled baggage mounted 11%. There is also a slight rise in the percentage of passengers bumped from flights. The airlines decreasing performance shows what many critics feared would happen when major carriers started merging six years ago.

Four mergers have been there among the eight largest airlines in the US since 2008. The industry's rate of on-time arrivals dropped from 78.4% in 2013 to 76.2% in 2104. Just two airlines enhanced their on-time arrivals rate last year. The two airlines are Frontier Airlines and JetBlue Airways.

The rate of customer complaints climbed from 1.13 per 100,000 passengers in 2013 to 1.38 in 2014. The majority of complaints registered by the US Department of Transportation was for flight problems, inlcuding baggage problems, delays, reservations, ticketing and boarding and customer service issues.