CFI Instrument Practical Test Standards,
FAA-S-8081-9B, June 2001
II. Technical Subject Areas
A. Aircraft Flight Instruments and Navigation Equipment
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2. Flight instrument systems and their operating characteristics
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d. Marker beacon receiver/indicators (also described under ILS)
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1) Ground elements
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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
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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
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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:
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Instrument Flying Handbook, FAA-H-8083-15, 1999
AIM 1-1-9