The common throttle lever for the four vertical lift engines was the only additional primary control in the cockpit; it was operated in a similar manner to that of the Collective pitch level of a rotorcraft. Two ways to control the attitude of the aircraft were required depending on its forward speed; aerodynamic surfaces were used during conventional flight, and air-jet nozzles for transitioning from horizontal flight, hovering and vertical flight. Bleed air from the four lift engines (approximately 10 per cent of the intake airflow) was supplied to the variable nose, tail and wing tip nozzles, for pitch, roll and yaw control at low speeds during which there would be insufficient airflow over the aerodynamic surfaces for conventional controls to be effective.