Flight sciences aircraft are used to expand the flight envelope. The nine flight sciences aircraft are composed of four F-35A conventional takeoff and landing, or CTOL, aircraft (including the first aircraft, called AA-1, which was manufactured before the results of a weight reduction program were applied to the F-35 design); three F-35B short takeoff/vertical landing, or STOVL, variants; and two F-35C carrier variant aircraft.
