In addition, a clearing signal is transmitted at one tenth of the power with a wider beam to prevent receivers from picking up the side lobes of the main beam. These are transmitted from co-located phased array antenna elements. One is amplitude modulated at 90 Hz, the other at 150 Hz. Two signals are transmitted on one of 40 ILS channels. Some runways have ILS only in one direction, this can however still be used for the opposite direction (with a lower precision) known as back beam or "Back Course" which is not associated with a glide path. In parts of Africa and Asia large airports may lack any kind of transmitting ILS system. An older aircraft without an ILS receiver cannot take advantage of any ILS facilities at any runway, and much more importantly, the most modern aircraft have no use of their ILS instruments at runways which lack ILS facilities. In aviation, a localizer is the lateral component of the instrument landing system (ILS) for the runway centerline when combined with the vertical glide path, not to be confused with a locator, although both are parts of aviation navigation systems.Ī localizer (like a glide path) requires both a transmitting airport runway system and receiving cockpit instruments. Emission patterns of the localizer and glide path signalsĪn instrument landing system localizer, or simply localizer ( LOC, or LLZ prior to 2007 ), is a system of horizontal guidance in the instrument landing system, which is used to guide aircraft along the axis of the runway.
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