Passengers board an American Airlines flight to Charlotte, North Carolina at San Diego International Airport on May 20, 2020 in San Diego, California.

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Slowly, the airline business is coming back to life as airlines set schedules for July that include more flights. The latest is American Airlines which says it plans to fly 55% of its domestic schedule in July, up dramatically from May when the airline flew 20% of its schedule compared to the same month a year ago.

“We’re seeing a slow but steady rise in domestic demand. After a careful review of the data, we’ve built a July schedule to match,” Vasu Raja, senior vice president of network strategy for American Airlines said in a release announcing the airline’s schedule.

American is Increasing flights at a more aggressive pace than its competitor United, which is ramping up its July schedule to 25% of what it flew during the same month in 2019.

Still, all U.S. airlines are cautiously optimistic more people will book flights this summer because passenger levels have been steadily increasing. In April, American averaged 32,154 passengers a day. From May 1 through the 23 its daily customer level more than doubled to 78,178, then jumped to 110,330 a day from May 24 to May 29.

While the numbers are encouraging, passenger levels in the U.S. remain extremely depressed due to the Covid-19 pandemic prompting millions of Americans to cancel trips or avoiding booking flights. According to the Transportation Security Administration, the number of passengers and airline crew members screened at U.S. airports is down more than 85% compared to the same time a year ago.

Are airlines getting ahead of themselves and bringing back too many flights too soon? With carriers still burning through tens of millions of dollars every day, airline executives say they are being judicious in their planning. They are also quick to point out more cities and states in the U.S. are opening up following Covid-19 shelter in place orders so there is pent up demand to travel.

OAG, which tracks the airline industry and flight schedules says the four biggest carriers in the U.S., United, American, Delta and Southwest, are boosting their schedules in June by 27% compared to May. Most of that increase is due to additional domestic flights. As for international routes, the growth in flights has been much more gradual due to depressed demand.

“The industry is showing some signs of recovery, but there are noticeable changes in consumer behavior,” said John Grant, OAG’s senior aviation analyst. “People are booking later, seeking more flexibility in their travel bookings and not committing to payment until the last minute.”

—CNBC’s Meghan Reeder contributed to this report.