Memorial Day weekend has produced the two busiest days for U.S. air travel since early March 2020.

About 1.96 million people passed through U.S. airport security checkpoints on Friday, and 1.90 million did so on Monday, according to the U.S. Transportation Security Administration.

Tuesday was also expected to be busy, as travelers returned home after the Memorial Day weekend. Analysts expect travel to continue rising slowly now that many Americans are vaccinated against COVID-19 and airlines are adding more flights.

In May, an average of 1.6 million people a day were screened at U.S. airports, down one-third from the 2.4 million people a day who went through TSA checkpoints in May 2019.

Airlines say bookings have surged thanks to COVID-19 vaccinations, a reduction in COVID-19 case counts, the lifting of travel restrictions and the reopening of tourist attractions.

But though travelers are coming back, air travel isn't quite back to normal.

For one, face coverings are still a must during air travel. The federal mask mandate on public transportation, including airports and airplanes, was due to expire May 11 but was extended through Sept. 13.

The number of incidents between passengers and airline crew members has increased substantially during the pandemic. Many of the scuffles have been about mask compliance.

The Federal Aviation Administration adopted a zero-tolerance policy in January and has issued hundreds of thousands of dollars in proposed penalties. And Southwest and American airlines announced they won't immediately resume alcohol service due to the uptick in in-flight incidents.