By CBSMiami.com Team

DALLAS (CBSMiami/AP) — There’s trouble in the skies as air travel in the U.S. is hits new pandemic-era highs, and airlines are scrambling to keep up with the summer-vacation crowds, including Florida-based discount carrier Spirit Airlines.

Citing weather and “operational challenges” Spirit Airlines canceled about one-third of its flights over the weekend. The airline is “working around the clock to get back on track,” Spirit spokesman Field Sutton said.

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Dozens of flights were canceled Sunday at Fort Lauderdale-Hollywood International Airport and Orlando International Airport.

“We needed to make proactive cancellations to some flights across the network, but the majority of flights are still scheduled as planned,” said Sutton.

Across the country, about 7,400 flights arrived at least 15 minutes behind schedule on Sunday — the government’s definition of late — and more than 900 were canceled, according to tracking service FlightAware,

Nearly half the cancellations were at Dallas/Fort Worth International Airport, which was hit with afternoon and evening thunderstorms. The airport is American Airlines’ largest hub.

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There have been at least 5,000 delayed flights on most days since early July, according to FlightAware figures. American, Southwest and Spirit are among airlines with the biggest problems.

At least 40% of Southwest and Spirit flights were delayed and 19% of Spirit flights were canceled Sunday. On Monday, Spirit canceled 32% of its flights by midday, which created long lines at ticket counters at Orlando International Airport.

The travel recovery faces a renewed public-health threat, as the number of new cases of COVID-19 continues to rise. The seven-day rolling average of new U.S. infections is around 80,000 a day, up nearly 150% from two weeks ago, although the increase in deaths is far smaller.

Airline officials say they haven’t seen bookings suffer because of the delta variant, although some have said it could delay the return of business travel, which airlines were hoping would gain speed this fall.

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(© Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)

CBSMiami.com Team