position is within |5 feet of the test altitude.
(c)
Release the self-test button. 1) Make sure you do not see the warning flag in the height
indicator. 2) Make sure the altitude shown goes back to -3(|3) feet.
(d)
Open this circuit breaker:
1) P18 Load Control Center - Left
a) RADIO ALTM-1 2) Make sure the warning flag comes into view.
(e)
Close this circuit breaker:
1) P18 Load Control Center - Left
a) RADIO ALTM-1 2) Make sure you do not see the warning flag. 3) Make sure the altitude shown is -3(|3) feet.
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(2) Use the first officer's height indicator to do the operational test for the first officer's radio altimeter system:
(a)
Push and hold the self-test button. 1) Make sure the DH light(s) go off. 2) Make sure the altitude pointer shows the self-test altitude
of 40(|2) feet.
3) Make sure the warning flag is in view.
(b)
Turn the cursor (index) control knob to increase the DH alert altitude. 1) Make sure the DH light(s) come on when the DH cursor is |5
feet or closer to the test altitude shown.
(c)
Release the self-test button. 1) Make sure you do not see the warning flag at the height
indicator. 2) Make sure the altitude shown goes back to -3(|3) feet.
(d)
Open this circuit breaker:
1) P6 Load Control Center - Right
a) RADIO ALTM-2 2) Make sure the warning flag comes into view.
(e)
Close this circuit breaker:
1) P6 Load Control Center - Right
a) RADIO ALTM-2 2) Make sure you do not see the warning flag. 3) Make sure the altitude shown is -3(|3) feet.
S 865-009
(3) Put the airplane and the radio altimeter system back to their usual condition.
(a) Release the test button. 1) Make sure the HI altitude pointer goes back to -3(|3) feet.
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737-300/400/500MAINTENANCE MANUAL
LOW RANGE RADIO ALTIMETER SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________________
1. General_______
A. The low range radio altimeter (LRRA) system provides vertical position information for use by the pilots during approach and landing phases of flight operation. The LRRA system provides measurement of absolute altitude (height above terrain) from 2500 feet to touchdown. LRRA valid flag alarm/failure warning, dc altitude, and vertical terrain clearance (altitude trip) outputs are available for use by other systems.
B. Two complete systems are installed. Each system consists of a receiver-transmitter (R/T), transmit antenna, receive antenna, display of absolute altitude (height above terrain) and decision height (DH) on the pilots EADI's, and selection and display of DH on the EFIS control panels located on the aft electronic panel (P8).
C. The LRRA systems supply LRRA fail warn or flag alarm, continuous dc altitude height above terrain, and fixed trip height above terrain inputs to the DFCS (digital flight control system), GPWS (ground proximity warn system), and the rising runway display on the EADI (if provided).
D. Each receiver/transmitter (R/T) provides continuous dc altitude (radio altitude [RA] height above terrain) to its associated EFIS symbol generator which processes it into a digital value displayed on the EADI (Fig. 1). A decision height (DH) value selectable on the EFIS control panel is directed by a 429 serial digital bus to its associated symbol generator. The symbol generator processes the DH value and converts it into a video signal which appears as a graphic/alphanumerical display on the associated EADI. When the airplane descends to the selected DH, the symbol generator provides a signal which causes the RA and DH characters and associated numeric values on the EADI to change color to yellow and blink for three seconds. This alerts the pilots that the airplane has descended to the DH value.
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