It seems Alaska Airlines' multi-year reign as the best airline in the United States has come to an end -- for now.

The 2019 Airline Quality Ranking, published Monday, shows Seattle-based Alaska Airlines dropped from first place in 2017 and 2018 to fourth place in 2019. Delta Airlines, second in 2018, took the top spot, followed by JetBlue and Southwest airlines.

Alaska did see a reduction the number of times passengers with confirmed reservations were denied boarding -- involuntary denied boardings, in industry terms -- from 0.32 to 0.23 per 10,000 passengers, but that was the only improvement for the airline compared to the previous year. More flights were delayed and considerably more bags were mishandled. The airline received about the same number of complaints both years.

The merger between Virgin America and Alaska Airlines also concluded in April 2018, meaning Alaska's score reflects both airlines' scores for the year. It's hard to say how much the merger directly impacted Alaska's ranking, but in 2018's AQR, Virgin ranked seventh. In 2017, Virgin took third place.