The airline industry breathed a sigh of relief after a busy holiday travel period that ended with more than 2.4 million people moving through airport security checkpoints Sunday, the busiest day for domestic air travel since the beginning of the coronavirus pandemic.

The sheer volume of people flying for the Thanksgiving holiday marked a milestone for air travel as passenger counts inch closer to levels not seen since the pandemic was declared. The Transportation Security Administration screened 20.9 million people during the 10-day travel period that ended Sunday, which is 89 percent of levels recorded before the pandemic, according to TSA spokeswoman Lisa Farbstein.

The increase signals robust demand for end-of-the-year travel as more people are eager for in-person celebrations nearly two years into the public health crisis.

The Thanksgiving travel surge was a test for airlines still struggling to rebuild operations while confronting a spike in unruly passenger behavior. Carriers were aided by stable weather that contributed to the largely smooth operations.

Airlines have sought in recent months to capitalize on a growing appetite for travel as the pandemic scrambled the industry and left some carriers stretched thin. American Airlines, Southwest Airlines and Spirit Airlines are among carriers that have stumbled, canceling thousands of flights and leaving customers stranded at airports this summer and fall, in part because of staffing shortages.

Sunday’s busy travel came with no major mishaps in the nation’s skies, airports or security lines, even as some travelers encountered long lines at checkpoints.

“The Thanksgiving holiday travel period went very smoothly, to the point that it was fairly uneventful as it relates to security screening,” Farbstein said. “We were very prepared for the larger volume and so were passengers.”

While Sunday was the busiest air travel day since the start of the pandemic, the second-busiest was Wednesday — the day before Thanksgiving.

Entering the Thanksgiving holiday, airlines did not schedule more flights than they could operate, said Bob Mann, an industry analyst with aviation consulting firm R.W. Mann & Co.

“We were very lucky,” he said. “The weather was on its best behavior and airlines had really doubled down on their ability to fly what they intended to.”

Also helpful, he said, were the robust financial incentives carriers offered workers to discourage absences and to encourage them to take extra shifts.

American Airlines flight attendants were offered triple their pay to work holiday flights if they have perfect attendance through early January 2022. Southwest offered flight attendants and pilots frequent flier miles and other crew extra pay for holiday shifts.

The incentives aimed to appease concerns of potentially chaotic disruptions during the holiday travel season. They also were an answer to unusual circumstances, according to industry experts and labor leaders who say that air travel demand continues to increase faster than airlines are able to ramp up their staffing.

Sara Nelson, international president of the Association of Flight Attendants-CWA, said earlier airline meltdowns showed workers were not willing to pick up overtime at the same pay rate as before the pandemic.

Even as air travel was spared major disruptions, it wasn’t free of hiccups.

Snow and rain led to delays in the Midwest, but it far less severe than anticipated as forecasters had predicted storms with the potential to create major travel problems. Elsewhere, a woman allegedly attacked two flight attendants on a Spirit Airlines flight from Fort Lauderdale to Nashville. She was restrained by another passenger and arrested by airport police for public intoxication.

Aside from those incidents, Nelson said the holiday travel period “was an off-the-charts successful operation … reliable, efficient, and on-time for travelers.”

She credited the federal relief program that kept aviation workers in their jobs during the pandemic with the industry’s ability to maintain successful operations. The industry received $54 billion in grants as part of three federal coronavirus aid packages — money that was designed to keep workers on the payroll and ensure carriers could recover from the verge of collapse when passenger counts fell more than 90 percent.

Lobbying group Airlines for America said the industry’s performance over the holiday week exceeded pre-pandemic years. In preparation for the holiday, U.S. carriers deployed additional aircraft to meet increased demand, hired and trained new employees and recalled workers who had taken voluntary leave, the trade group said.

On-time arrivals of domestic flights between Nov. 17 and Sunday were at 85 percent, while 99.7 percent of scheduled flights were completed, according to data from Anuvu reported by A4A.

The spike in domestic travel comes as virus transmissions have fallen from their peak, vaccinations are more widely available to children and many pandemic-related restrictions have been lifted. But it also precedes new travel restrictions announced over the weekend, generally affecting international travel, to slow the spread of the omicron coronavirus variant.

After a successful Thanksgiving holiday, industry analysts and labor leaders say airlines are better positioned going into the Christmas and New Year’s holidays. The amount of passenger traffic is traditionally lower and more spread out. Worker incentives are expected to continue through early January and carriers are likely to increase staffing levels.

Still, Mann, of R.W. Mann & Co., said it’s no time to scale back preparations, considering that a key to success in recent days was the lack of unfavorable weather.

“I wouldn’t be taking my eye off the ball at this point because all you need is bad weather and it all goes south really quickly,” he said.