ILS Markers RNAV
ILSILS —Instrument Landing System markers are an older system used to tell pilots how far from touchdown they were. There are several exam facts that need to be known about these beacons, including:
- The approximate range from touchdown.
- The light colour.
- The audio code and frequency that illuminate and sound as you pass over them.
- The frequency of modulation.
This data is summarised in the table below.
|Outer Marker||Middle Marker||Inner Marker|
|Audio code||Dashes only||Dots and dashes||Dots only|
|Audible frequency||400 Hz||1300 Hz||3000 Hz|
|Modulating frequency||75 MHz||75 MHz||75 MHz|
|Range to touchdown||6.5-11km (often represented as 4nm)||1050 m||75-450 m|
Do not get the audio frequency for each marker confused with this modulation frequency. The audio frequency changes (becoming higher in pitch each time), but all the markers are modulated at 75MHz.
Remember that audio frequencies must be audible, so they are measured in Hz, not MHz.