Optical landing system

An optical landing system (OLS) (nicknamed "meatball" or simply "ball") is used to give glidepath information to pilots in the terminal phase of landing on an aircraft carrier. From the beginning of aircraft landing on ships in the 1920s to the introduction of OLSs, pilots relied solely on their visual perception of the landing area and the aid of the Landing Signal Officer (LSO in the U.S. Navy, or "batsman" in the Commonwealth navies). LSOs used coloured flags, cloth paddles and lighted wands. The OLS was developed after World War II by the British and was deployed on U.S. Navy carriers from 1955. In its developed form, the OLS consists of a horizontal row of green lights, used as a reference, and a column of vertical lights. The vertical lights signal whether the aircraft is too high, too low, or at the correct altitude as the pilot descends the glide slope towards the carrier's deck. Other lights give various commands and can be used to require the pilot to abort the landing and "go around." The OLS remains under control of the LSO, who can also communicate with the pilot via radio. An optical landing system has several related components: the lights used to give visual cues to approaching aircraft, the light control system, and the mounting system. At least three sets of lights are used, regardless of the actual technology: Datum lights – a horizontal row of green lamps used to give the pilot a reference against which he may judge his position relative to the glide slope. Ball (or "meatball"; also known as "the source") – indicates the relative position of the aircraft with reference to glide slope. If the aircraft is high, the ball will be above the datum lights; if the aircraft is low, the ball will be similarly below the datum lights. The further the aircraft is from the glide slope, the further the ball will be above or below the datum lights. If the aircraft gets dangerously low, the ball appears red. If the aircraft gets too high, the ball appears to go off the top.