Using television as an instrumental aid, light helicopters can be hovered with considerable accuracy above a known ground point at altitudes of the order of a thousand metres above ground level. The image from a vertically-aimed ground-based television camera is transmitted to the helicopter and displayed on a receiver placed in front of the pilot, who uses the image of the helicopter for guidance to the hover point. With this system, the hover point has been maintained within ±1.2 m (4 feet) for periods of up to 2.5 minutes at 1200 m (4000 feet) above ground level.