Definition of Outer Marker
The Outer Marker refers to a critical component of an Instrument Landing System (ILS) approach that is positioned at or close to the glideslope intercept altitude. It is generally situated on the extended centerline of the runway, approximately four to seven miles from the runway threshold. The main purpose of the Outer Marker is to provide pilots with a radio frequency signal that indicates they are at a specific point on the approach path, allowing them to approach the runway in a safe and controlled manner. Pilots must tune their onboard receivers to the specific frequency of the Outer Marker to receive the signal. Upon receiving the Outer Marker’s signal, pilots can begin their final descent to the runway, as well as activate the aircraft’s landing gear and lights. Therefore, it plays a pivotal role in enabling the safe landing of an aircraft in low visibility conditions, such as during fog or heavy rain.
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