ATLANTA — The Delta Airlines’ senior vice president of flight operations, John Laughter, said in a memo that the airline is bringing back 400 pilots to active flying by this summer, “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.

U.S. passenger traffic so far in January is down 61% from a year ago.