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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
RISING RADIO ALTITUDE
RUNWAY (RA) - AIRPLANE
AT REST ON GROUND
EFIS ELECT ATT DISPLAY
INDICATOR (EADI)
DH SET CONTROL KNOB
DH RESET PUSHBUTTON
EFIS CONTROL PANEL
RECEIVER-TRANSMITTER (R/T)
Low Range Radio Altimeter System - Component Location
Figure 1
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
C. The test connector on the front panel is used to connect a test set for checks of fixed height-above-terrain trips used by the flight control system and other systems on the airplane, and for other LRRA system tests.
LRRA System Control Interface
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A. EFIS Control Panel (RA Related Functions)
(1) The EFIS control panel provides selection of the decision height (DH). DH can be selected from -20 to +999 ft. by turning the DH select knob. DH is read from the 3-digit DH REF LCD display. The RST switch, when pressed, terminates the DH alert at the associated EADI.
B. The captain's and F/O's EFIS control panels are located on the pilots'
control stand aft electronics panel P8.LRRA System Radio Altitude Indication Interface
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A. EADI
(1)
Radio altitude (height above terrain) and DH data is displayed in the lower right corner of the EADI's.
(2)
For altitudes above 2500 feet, the RA display is removed. The DH display shows the letters DH and the decision height set on the EFIS control panel in green.
(3)
For altitudes between 2500 feet and DH value, the RA display is shown in white numerals. When the airplane descends to the DH value, the letters DH and the RA value blink (yellow) for three seconds, then letters DH disappear and the decreasing RA value remains yellow.
Antenna
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A. The antennas are linearly polarized horns. Two identical antennas are used in each system of the dual LRRA system, one for transmitting and one for receiving. The antennas are connected to the receiver-transmitter through specific length coaxial cables and are flush mounted on the lower fuselage centerline as follows:
TRANSMIT ANTENNA NO. 1 STA 450 RECEIVE ANTENNA NO. 1 STA 430
TRANSMIT ANTENNA NO. 2 STA 390 RECEIVE ANTENNA NO. 2 STA 410
Operation (Fig. 2)
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A. Altitude Measurement Operation
(1) The LRRA system provides altitude data when power is applied by separate circuit breaker to the receiver-transmitters. Low voltage power is then supplied to all circuits in the receiver-transmitters and to the height indicators. Each LRRA system is turned on by closing its circuit breaker. Each LRRA system (LRRA1 - Captain's, LRRA2 - F/O's) operates independently of the other.
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