A United Airlines Boeing 737-800 sits at a gate after arriving at O’Hare International Airport in Chicago, Illinois, US, June 5, 2019. [Photo/Agencies]

US airlines plan to call back thousands of employees as their chief executives say they are confident the industry could rebound by summer from the coronavirus pandemic that has threatened to decimate it.

Passenger traffic is still down by more than 40 percent compared with 2019, but Southwest Airlines said it will reinstate 2,700 flight attendants by June who were on voluntary leave. American and United airlines each plan to hire around 300 new pilots this year, according to The New York Times.

In the first quarter of this year, Delta, American and United lost more than $1 billion each. But their executives are optimistic that the rest of the year will be profitable as the race to vaccinate the US population has accelerated the potential for people to travel. At least 48.3 percent of US adults have received at least one dose of a coronavirus vaccine, according to the Centers for Disease Control and Prevention.

“A year after the onset of the pandemic, travelers are gaining confidence and beginning to reclaim their lives. Delta is accelerating into the recovery,” said Delta CEO Ed Bastian when reporting the carrier’s first-quarter financial results. Delta, which has clawed back about 85 percent of its domestic leisure sales this year, said if the trend continues, the airline would be profitable by summer.

American Airlines said this month that it expected to sell more than 90 percent as many tickets within the US this summer as it did in the summer of 2019.

United CEO Scott Kirby said that the carrier could beat its 2019 profits in 2023.

Southwest CEO Gary C. Kelly told investors and analysts: “I’m relieved, I’m optimistic, I’m enthused, I’m grateful and I’m especially thankful to our tens of thousands of employees. We’ve got a long way to go but I’m very, very confident.”

Southwest, which carried more passengers than any other US airline in 2019, managed to turn a small profit in the first three months of this year, the first major US airline to do so since the pandemic began.

In March, ticket sales for airlines were up, and at least 1 million people were screened at airports per day, according to the Transportation Security Administration.

Airlines for America, a trade organization for domestic airlines, said that Alaska Airlines, Allegiant, Hawaiian Airlines, JetBlue and Spirit ended last year with $163 billion in debt, up from $105 billion in 2019.

The International Air Transport Association (IATA) said that while it also sees hopeful signs, net airline industry losses will be $47.7 billion in 2021, an improvement on the estimated loss of $126.4 billion in 2020.

“There is optimism in domestic markets where aviation’s hallmark resilience is demonstrated by rebounds in markets without internal travel restrictions,” said Willie Walsh, director general of IATA. “Government-imposed travel restrictions, however, continue to dampen the strong underlying demand for international travel.”

Signs of a resurgence for the sector are a far cry from the dire predictions put forward last year by one top executive that it was “most likely” that at least one US airline could go bankrupt.

David Calhoun, president and CEO of aircraft maker Boeing, told NBC in May 2020: “The threat to the airline industry is grave. There’s no question about it. And apocalyptic does actually accurately describe the moment,” Calhoun said of the impact of the coronavirus.

US airlines received billions of dollars from the federal government to stay afloat. Congress provided more than $50 billion in aid to help keep baggage handlers, pilots and flight attendants employed. Airlines also received $25 billion in government loans.

Americans are currently traveling domestically and to Mexico, the Caribbean and Latin America.

In July, American Airlines said it plans to fly about 60 percent fewer seats on longer overseas trips, compared with the same month in 2019. United said last week that it plans to run flights to Croatia, Greece and Iceland this summer. It will increase its domestic flights by 20 percent to countries close to North America.

In March 2020, the European Union banned Americans from all nonessential travel to Europe. But this week, the head of the bloc’s executive body said Americans who have been fully vaccinated against the coronavirus may be able to visit countries in the European Union this summer.

Ursula von der Leyen, president of the European Commission, told The New York Times on Sunday that immunization with a vaccine that has been approved by the bloc’s drug regulator, the European Medicines Agency, “will enable free movement and the travel to the European Union”.

The agency has approved each of the three coronavirus vaccines available in the United States, which were developed by Moderna, Pfizer-BioNTech and Johnson & Johnson.

Agencies contributed to this story.