This is the worst airline in the U.S., according to a new ranking — and it's not Spirit or Frontier

When it comes to low-cost airlines, American fliers usually praise JetBlue, and despise Spirit Airlines and Frontier Airlines.

But if you took to the sky in 2021, JetBlue might have let you down — with large numbers of brutal, hours-long delays and frustrating cancellations, according to a new study.

The Long Island City, New York-based airline recently dropped to the lowest spot on The Wall Street Journal's annual ranking of U.S. airlines, falling behind both Spirit and Frontier. American Airlines almost incurred a similar fate, tying with Frontier for third-to-last.

Delta Air Lines claimed the top spot on the list, followed by Alaska Airlines and Southwest Airlines.

The list, released on Jan. 28, ranked the nine largest U.S. airlines based on their performance in 2021 across seven categories: on-time arrivals, cancelled flights, extreme delays, tarmac waits longer than two hours, mishandled baggage, passengers being involuntary bumped from flights and customer complaints.

It relies on data from the U.S. Department and Transportation and aviation analysis software firm masFlight.

Here are the overall rankings:

1. Delta Air Lines

2. Alaska Airlines

3. Southwest Airlines

4. United Airlines

5. Allegiant Air

Tie-6. American Airlines

Tie-6. Frontier Airlines

8. Spirit Airlines

9. JetBlue Airways

The analysis found that JetBlue had the highest rate of extreme delays and incidents where passengers had to wait on the tarmac for at least two hours. JetBlue also had the second-fewest on-time arrivals, behind only Allegiant Air, and the second-most customer complaints behind Spirit, according to the ranking.

It wasn't all bad news for JetBlue: The carrier had the fourth-fewest involuntary bumpings and cancellations. JetBlue did end the year by cancelling about 1,280 flights from Dec. 30 through Jan. 13 after a surge in Covid-19 infections, but most of those cancellations didn't appear in the analysis, which was restricted to 2021 data.