American Airlines plans to reactivate most of its aircraft in the second quarter, citing strong demand and booking performance and reflecting a generally bullish attitude U.S. carriers are now showing for the upcoming summer travel season.

In a filing with the U.S. Securities and Exchange Commission on Monday, American noted “recent strength in domestic and short-haul international bookings” as vaccine distribution has grown. As of last week, the carrier’s seven-day moving average of net bookings—which factors in new bookings minus cancellations—recovered to 90 percent of what they were for the same period in 2019. American’s domestic load factor was at 80 percent last week, although capacity for the full first quarter is projected to be 40 percent to 45 percent lower than the first quarter of 2019.

American “expects this strength in bookings to continue through the end of the first quarter and into the second quarter,” although “visibility regarding forward bookings remains limited,” according to the filing.

The carrier is not alone in its cautious optimism. OAG reported that global capacity this week is up 4 percent compared with last week to 62.1 million seats, leading to the best week airlines have seen in terms of capacity in more than a year, if airlines do not adjust their schedules. Capacity this week is up in each of the top 20 markets around the world except Brazil, which is facing a severe crisis in terms of Covid-19 spread and hospitalizations.

“It is very early, but airlines appear to remain generally bullish around the summer season with capacity trending upwards in every month of the next two quarters,” OAG analyst John Grant wrote in his weekly update on Monday. “Certainly, airline network planners would appear to be injecting more capacity into a vaccine-populated world.”

Airlines Reporting Corp. also reported that overall air ticket sales by U.S. travel agencies have improved in recent weeks compared with the beginning of the month. Last week, for example, the number of tickets sold was down 51.2 percent compared with the same week in 2019—an improvement from the first week of the month, when they were down 56.4 percent.

Corporate travel, however, largely remains absent from the recovery. ARC reported that tickets sold by online agencies were down 27 percent compared with 2019 levels at the end of last week, an improvement of 10 percent points compared with the beginning of the month. Leisure agencies had improved by about 4 percentage points for that same period. Corporate agencies, meanwhile, have remained at more than 80 percent below 2019 levels for the entire month, with little variance from week to week.