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 E.  When RA or DH values are invalid due to equipment malfunction or loss of radio altitude signal, the characters RA and/or DH are enclosed in a yellow box and the numerical values are not displayed. If the values become valid, the normal alphanumerical display is resumed on the EADI. The EFIS transfer switch on the overhead P5 panel allows normal (separate) usage of RA data from the LRRA R/T's (LRRA-1, captain's) (LRRA-2, F/O's) to be directed to its associated EADI, or allows both EADI's to operate from LRRA-1 or LRRA-2 RA input.
 2.  Receiver-Transmitter (Fig. 1)____________________
 A.  The receiver-transmitters are located side-by-side on shelf four of the E2 electronic rack. All electrical connections to the receiver-transmitters are made through a connector located on the R/T rear panel. An auxiliary connector located on the R/T front panel is provided for connection to test equipment.
 B.  Fault lights and a press to monitor switch are provided on the R/T front panel as aids to fault isolation.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.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

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A09630
 3.
4.

5.

6.

A
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
_____________________________
 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
_______________________________________________
 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
_______
 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)
_________
 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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