Instrument landing system

In aviation, the instrument landing system (ILS) is a precision radio navigation system that provides short-range guidance to aircraft to allow them to approach a runway at night or in bad weather. In its original form, it allows a pilot, through a cockpit mounted instrument in the aircraft that displays lateral and vertical guidance indications (needles),, to approach until the aircraft is 200 feet (61 m) over the ground, within 1⁄2 mile (800 m) of the runway.

Source: Wikipedia — Instrument landing system (CC BY-SA 4.0)