(2)  Self-Test Operation (Fig. 3)
 (a)  
Actuating the test switch at the associated height indicator causes a bias signal to be applied to the circulators in the receiver-transmitter. The resultant field set up in the circulators switches the circulators from the antenna system to the delay line. The delayed signal is processed through the receiver circuits in the same manner as a normal altitude signal. During self-test, the indicator should display the test altitude of 100 |10 feet.

 (b)  
Self-test of LRRA systems 1 and 2 is initiated at the captain's and first officer's height indicator, respectively. When the test button is depressed, a ground signal is applied through a relay in AFC-2 accessory box to the test circuits in the receiver-transmitter. The relays, one for each LRRA system, inhibit the self-test command after glide slope capture by the autopilot system.

 EFFECTIVITY

 AF ALL; SN351-399; MD ALL;  CONFIG GN ALL; AT ALL; VM ALL  03 Page 13  Aug 25/88

34-33-00
 (c)  On SN 351-399, there are no provisions in the pilots' control cabin for self-testing LRRA system 3.
 (3)  Warning Flag, and Integrity Monitor Operation (Fig. 3)
 (a)  
A warning flag will come into view on a height indicator to indicate unsatisfactory system performance. For LRRA system 3 installed on SN 351, a failure annunciator on the pilots' center instrument panel P2 will also announce unsatisfactory system performance by changing from a black to a red display. The height indicator flag control circuit functions as a monitor of the servo loop, the ac voltage for the power supply, the flag alarm voltage, and the +30-volt dc reference voltage. When the signals applied to the null detector in the indicator differ by more than the predetermined value, or if any of the other inputs to the flag control circuit are missing, the flag solenoid is de-energized and the warning flag comes into view.

 (b)  
The receiver-transmitter monitor circuits check circulator switching, main servo loop tracking, self-calibration loop, time-to-voltage converters, and antennas and coaxial cables for proper operation and provide flag warning information to the flag alarm circuits.

 (c)  
In the flag alarm circuits, the warning information is processed to provide +30-volt dc (valid) and 0-volt (alarm) flag alarm signals. The flag alarm signal is applied to the height indicator and other airplane using equipment (Fig. 2). When the alarm condition is detected, the dc altitude signals are driven to a maximum and all altitude trip circuits are opened.

 (d)  
In the height indicator, the alarm signal is applied to the warning flag solenoid. The +30-volt dc signal energizes the solenoid causing the warning flag to retract from view. The alarm condition (0-volt signal) de-energizes the solenoid causing the warning flag to appear. The flag alarm signal is routed through relay contacts in the indicator monitor circuits prior to being applied to the flag solenoid.

 (e)  
The indicator monitor circuit evaluates the dc reference voltage applied to the DH and servo potentiometers and the output of the pointer drive comparator for an out-of-tolerance condition. If a malfunction is detected, the logic circuit removes the actuating signal from the switch causing the relay to de-energize. This removes the valid signal and applies the alarm signal to the flag solenoid.

 (f)  
The three receiver-transmitter fault annunciators are magnetic latching devices. The annunciators can be reset by depressing the adjacent RESET switch. The annunciators indicate a malfunction in the receiver-transmitter (R/T), height indicator (IND), or antennas and coaxial cables (ANT).

 B. Control
 (1)  Turn On Procedure
 (a)  
Apply electrical power to airplane (Ref 24-22-00).

 (b)  
Provide equipment cooling air (Ref 21-58-00).

 EFFECTIVITY
 AF ALL; SN351-399; MD ALL;  CONFIG GN ALL; AT ALL; VM ALL  03 Page 14  Aug 25/88

34-33-00
 (c)  
Close ALTM LOW R1 and ALTM LOW R2 circuit breakers on panel P7. On SN 351-399, also close ALTM LOW R3 circuit breaker on circuit breaker panel P126.

 (d)  
Rotate height indicator DH control knob clockwise to turn on system (Ref Fig. 1).

 (e)  
The height indicators should display an altitude between -3 and -11 feet with the warning flag out of view. On SN 351, the LRRA-3 failure annunciator should display a valid (black) indication.

 EFFECTIVITY

 AF ALL; SN351-399; MD ALL;  CONFIG GN ALL; AT ALL; VM ALL  01 Page 15  Aug 25/88

34-33-00
 LOW RANGE RADIO ALTIMETER SYSTEM - DESCRIPTION/OPERATION
　
中國航空網 www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：747飛機維護手冊AMM CHAPTER 34 - NAVIGATION 第34章導航2(64)