Marker Beacon

 

II. Technical Subject Areas A. Aircraft Flight Instruments and Navigation Equipment 2. Flight instrument systems and their operating characteristics d. Marker beacon receiver/indicators (also described under ILS) 1) Ground elements a) Low-powered VHF transmitter directs its signal upward in a small fan-shaped pattern b) Outer marker (OM) located 4-7 miles from airport near position where aircraft at appropriate altitude will intercept glidepath c) Middle marker (MM) located approximately 3,500 feet from landing threshold at position where glide-slope centerline is about 200 feet above touchdown zone elevation d) Inner marker (IM) located at decision height on glidepath for Category II approach e) There may be a back-course marker to indicate the back-course FAF 2) Airborne marker beacon receiver indicates, aurally and visually, when the aircraft is directly over the transmitter facility a) OM - low-pitched tone, continuous dashes, two per second and purple or blue light ------ b) MM - intermediate tone, alternate dots and dashes, 95 .- per minute and amber light .-.-.- c) IM - high-pitched coninuous dots, six per second and white light ...... d) BCM - (back-course marker) - high-pitched pairs of dots, 72-75 pairs per minute and white light .. .. .. e) Many units allow selection of 2 sensitivities i) Low gives sharpest indication of position and should be used during an approach ii) High provides an earlier indication that aircraft is approaching the beacon References: Instrument Flying Handbook, FAA-H-8083-15, 1999 AIM 1-1-9