Instrument landing system localizer

A localizer (like a glide path) requires both a transmitting airport runway system and receiving cockpit instruments.

In parts of Africa and Asia large airports may lack any kind of transmitting ILS system.

The cockpit instrument uses the difference between the modulation strengths of the two received signals to indicate left or right deviation from centerline.

With the indicators added to the artificial horizon (and to the compass), the pilot can theoretically watch the attitude simultaneously with the localizer and glide path.

In modern cockpits, the localizer is seen as a colored dot (usually in the shape of a diamond) at the bottom of the artificial horizon.

If the transmitted localizer beam, which usually, but not always, is directed in the heading of the runway extension (exceptions exist, for instance, in Innsbruck, Austria and in Macao).

But if the aircraft is located a little left of the beam, the marker will appear to the right on the localizer gauge scale in cockpit.

But in older style cockpit instrumentation, the localizer also appears as an arrow in the gyro compass below the artificial horizon.

This older ILS instrumentation system was omitted around the same time as jet airliners like Boeing 707 and DC 8 were introduced.

The cockpit ILS indicators are not to be confused with the flight director, which also places vertical and horizontal lines on the artificial horizon.