an ILS (instrument landing system) navigational facility in the terminal area navigation system located at 4 to 7 miles (6 to 11 km) from the runway edge on the extended centerline
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It transmits a 75-MHz fan-shaped radiation pattern, modulated at 400 Hz (fan markers and station markers radiate at 3000 Hz, whereas middle markers do so at 1300 Hz), keyed at two dashes per second, and received by compatible airborne equipment. It indicates to the pilot, both aurally and visually, that he or she is passing over the facility and can begin the final approach.
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Valdkond ICAO lisade põhjal loodud klassifikaatori järgi: Lennundusside (telekommunikatsioon)
Kaugmarker (OM) asub tavaliselt 4-7 NM, keskmarker 0,6 NM ja lähimarker asub keskmarkeri ja raja läve vahel, 250-1500 ft raja lävest. Kaugmarker tähistab glissaadi sisenemise punkti ja selle ületamisel võib kuulda signaali sagedusel 400 Hz 2 kriipsu sekundis, kriipsudega sünkroonselt vilgub sinine markeri lamp armatuurlaual.
As mentioned, an outer marker beacon transmitter is located 4–7 miles from the threshold. It transmits a 75 MHz carrier wave modulated with a 400 Hz audio tone in a series of dashes.
