ATLANTA (AP) — Delta Air Lines plans to return 400 pilots to regular flying duties by this summer in a sign that it expects travel to increase over the peak vacation season from current, low pandemic levels.

The airline’s senior vice president of flight operations, John Laughter, said in a memo that the airline is bringing back pilots to active flying “well ahead of when we originally estimated.”

The 400 are not new hires; through March, they are being paid with taxpayer money that Delta received as part of $15 billion in additional federal aid to the airline industry. Delta had threatened to furlough about 1,700 less-senior pilots last fall but backed down after their union agreed to concessions including reduced pay and removal from active flying.

Union spokesman Chris Riggins said the Air Line Pilots Association was encouraged by Delta’s decision.

U.S. passenger traffic so far in January is down 61% from a year ago. Delta and United are forecasting continued weak travel demand through March, but industry officials expect improvement as more people are vaccinated against COVID-19.

Delta shares were down 2%, and other airline stocks fell even more in afternoon trading as countries tightened travel restrictions to curb the spread of new COVID-19 variants. The White House announced Monday that President Joe Biden will ban travel of non-U.S. citizens from Brazil, South Africa, the United Kingdom and more than two dozen other European countries.