WASHINGTON — The first flight of the B-21 Raider stealth bomber will occur a few months later than the Air Force anticipated, the service’s secretary said Wednesday. “It’s slipped from the original schedule — that we were using as a schedule to manage by — by a few months,” Frank Kendall said at the McAleese & Associates conference in Washington, before noting he is recused from making decisions on the program due to his previous consulting work with B-21 manufacturer Northrop Grumman. “It’s