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The blue outer marker lamp has an associated 400 hertz 'dash' tone.
The lamp and tone are keyed at a rate of two per second when the
aircraft is in the range of the outer marker.
The amber middle marker lamp is coupled with a 1300 hertz tone,
keyed alternately with short 'dot' and long 'dash' bursts at 95
combinations per minute.
The white inner marker lamp has a 3000 hertz 'dot' tone. The lamp
and tone are keyed at a rate of six times per second.
The sensitivity (SENS) button can be used to change the marker beacon
receiver sensitivity to high or low. Use HI sensitivity only when navigating
using fan markers on airways. For normal ILS marker beacons the sensitivity
should always be set to LO.
Holding the SENS button for one second illuminates all three lamps
simultaneously to assure the lamps (internal and external) are in working
order. It will also cause the marker audio to mute for that beacon; the next
beacon received will reactivate the audio. Releasing the SENS button restores
the last sensitivity.
