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NEW YORK, NY - AUGUST 8: Travelers check the Delta departures board at LaGuardia Airport , August 8, 2016 in the Queens borough of New York City. Delta flights around the globe were grounded and delayed on Monday morning due to a system outage.
NEW YORK, NY - AUGUST 8: Travelers check the Delta departures board at LaGuardia Airport , August 8, 2016 in the Queens borough of New York City. Delta flights around the globe were grounded and delayed on Monday morning due to a system outage.
Drew Angerer—Getty Images

Snowstorms in the winter and severe thunderstorms in the summer take the blame for a lot of the monstrous flight delays that leave thousands of people cooling their heels in the airport for hours or even days. But as it turns out Mother Nature is just a scapegoat for the real perpetrator of airline delays: the airlines themselves.

According to the U.S. Department of Transportation, airline mistakes like computer glitches — such as the days-long outage that grounded around 2,000 Delta flights earlier this month — maintenance and mechanical problems, crew issues and the like are now the biggest reason you're standing in front of that blue departures board, squeezing the handle of your carry-on and cursing your luck.

It's not always easy to figure out what causes delays, Bloomberg explained, since there can be ripple effects and sometimes flight delays have more than one cause.

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But numbers from the DOT's Bureau of Transportation Statistics do make it clear that airlines are often dealing with self-inflicted problems. Last year, airline mistakes led to more than 323,000 delays, according to the BTS, accounting for about a third of delay time. Bad weather was responsible for about 5% of delay time, with about 36,000 flights affected.