Aids to final approach and landing ILS

By using VOR and DME a pilot knows he is on the correct course and he also knows his distance to the VOR/DME station. With this equipment the aircraft will be brought directly over the VOR/DME station from which point an approach can usually be made.

In poor weather conditions, however, a more precise (1) landing aid is used. The ILS (2) is the ICAO (3) approved international standard electronic landing aid and is installed at nearly all major aerodromes.

The ILS functions with equipment in the aircraft and on the ground. On the aerodrome a localizer (4) transmits a narrow radio beam (5) and another transmitter provides a glide path (6) at a fixed angle of approach. On the aircraft instrument panel an ILS indicator (7) shows the aircraft's position in relation to the centre line of the runway and to the glide path. The ILS can, therefore, guide the aircraft along the proper approach path down to a point where the pilot must be able to see the ground and be able to continue his approach to land. If he cannot see the ground at this point, he must decide to overshoot (8), go around and try to land again.

		Too high. Correct is azimuth. Too low. Too far to the left

In addition to the ILS localizer and glide path, an ILS installation also comprises two or three fan markers (9): one called the outer marker (10) is situated from four to six miles from the threshold (11) of the runway; a second called the middle marker (12) is situated approximately half a mile from the threshold of the runway, and the third, called the inner marker (13) (installed only when required) is about 1,000 feet from the threshold of the runway These fan markers alert the pilot of his passing over these markers by causing a light on the aircraft instrument panel to flash on and off while he is over each marker.