(2)
Test ILS buffer amplifier operation as specified in VOR/ILS Navigation System - System Test procedures.
(3)
Remove electrical power if no longer required (Ref 24-22-00).
EFFECTIVITY
AT ALL; LH 011-099; AZ 221-299; SN 351-399; 08 Page 401 IB 406-499 Apr 25/86
34-31-18
MARKER BEACON SYSTEM - DESCRIPTION OPERATION
____________________________________________
1. General (Fig. 1)
_______
A. The marker beacon system provides visual and aural indications when the airplane flies over ground based 75 MHz marker beacon transmitters. These transmitter installations include airways fan markers, station location Z markers, and instrument landing system (ILS) middle and outer markers.
B. The marker beacon system consists of one 75 MHz receiver, a receiving antenna, two sets of marker beacon indicator lights, and a sensitivity switch. The system receives power from the standby bus.
C. The ground marker beacon transmitters all operate on a fixed frequency of 75 MHz and are modulated by one of four audio signals, depending on the type of marker beacon. The signals, received by the airborne receiver as the airplane passes over the transmitter, illuminate the appropriate indicator lights. A corresponding audio signal is made available to the crew through the flight interphone system by actuation of the marker beacon control (MKR) on the audio selector panels. The four types of marker beacons with their tone frequency and indicator light color are as follows:
(1)
ILS Outer Marker - An intermittent 400-Hz tone with the blue indicator light flashing.
(2)
ILS Middle Marker - An intermittent 1300-Hz tone with the amber light flashing.
(3)
Airways Fan Marker - An intermittent 3000-Hz tone with the white indicator light flashing.
(4)
Station Location Z Marker - A steady 3000-Hz tone with the white indicator light steadily illuminated.
2. Antenna (Fig. 1)
_______
A. The antenna is a flush-type unit located on the bottom centerline of the fuselage at body station 1025, and is connected to the receiver by a coaxial cable.
3. Receiver (Fig. 1)
________
A. The marker beacon receiver is located on shelf E3-6 next to stanchion No. 3 in the main equipment center. The receiver operates at a fixed-tuned frequency of 75 MHz.
4. Indicator Lights (Fig. 1)
________________
A. Two sets-of-three indicator lights are installed, one set on the captain's flight instrument panel and the other set on the first officer's instrument panel. The lights are covered by white, blue, and amber lenses to annunciate the airways, outer, and middle markers respectively and are of the push-to-test type.
5. Sensitivity Control (Fig. 1)
___________________
A. A MARKER sensitivity switch is installed on the first officer's flight instrument panel. The LOW and HIGH positions of the switch indicate the degree of receiver sensitivity and are normally used when the airplane is flying at low and high altitudes respectively.
6. Operation
_________
A. Functional Description (LH ALL; AF 172-182, 185-199; AZ ALL; SN ALL; GN ALL; AT ALL; MD ALL; VM ALL) (Fig. 2, Sheet 1)
EFFECTIVITY
ALL 26 Page 1 Sep 25/9434-32-00
CAPTAIN'S FIRST OFFICER'S INSTRUMENT PANEL
INSTRUMENT PANEL SEE A
SEEA B
AIRWAYS
OUTER MARKER
HIGH
MIDDLE
LOW
CAPTAIN'S MARKER LIGHT SET
(FIRST OFFICER'S IDENTICAL)
A
SENSITIVITY SWITCH
B
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