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.
Lights ,
VASI, and OLS meatball and datum lights 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. •
Wave-off lights – red flashing lamps which, when lit, indicate that the pilot must add full power and go around – a mandatory command. When the wave-off lights are lit, all other lamps are extinguished. The wave-off lights are operated manually by the LSO. Some (particularly later) optical landing systems include additional lamps: •
Cut lights – Green lamps used to signal different things based on where the approaching aircraft is in its approach. Named for its original use in commanding aircraft on pre-angled deck landings to throttle down to idle prior to landing; still in use for crash-barrier landings. Early in a no-radio or "zip-lip" approach (which is routine in modern carrier operations), cut lights are flashed for approximately 2–3 seconds to indicate that the aircraft is cleared to continue the approach. Subsequent flashes are used to prompt the pilot to add power. The longer the lights are left on, the more power should be added. Cut lights are operated manually by the LSO. •
Emergency wave-off lights – Red lamps that have the identical function as Wave-Off Lights, but use an alternate power source. Not normally used.
Light controls is set. Collectively, the apparatus that the lights are mounted on is called the "lens". It is turned on/off and brightness is adjusted at the lens itself for ground-based units, and remotely for shipboard units. In both cases, the lens is connected to a hand-controller (called the "pickle") used by the LSOs. The pickle has buttons that control the wave-off and cut lights.
Light mounting For shore-based optical landing systems, the lights are typically mounted on a mobile unit that plugs into a power source. Once set up and calibrated, there are no moving parts to the unit. Shipboard units are much more complicated as they must be gyroscopically stabilised to compensate for ship movement. Additionally, shipboard units are mechanically moved (the "roll angle") to adjust the touchdown point of each aircraft. With this adjustment, the tailhook touchdown point can be precisely targeted based on the tailhook-to-pilot's-eye distance for each aircraft type. ==Mirror landing aid==