(2)  
Depress and hold the bank of captain's and first officer's A/P APD annunciator light caps. Check A/P APD annunciator lights are on bright.

(3)  
Position the MASTER DIM/TEST switch on the P2 panel to DIM while holding A/P APD light caps down. Check A/P APD annunciator lights dim.

(4)  
Position the MASTER DIM/TEST switch to BRT. Check A/P APD annunciator lights return to bright.

(5)  
Release the A/P APD light caps.

(6)  
Remove the electrical power if it is no longer necessary.

500 
May 01/01  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-26-61 Page 403 

NAVIGATION WARNING SYSTEM - DESCRIPTION AND OPERATION
1. General
A.  The navigation warning system compares the output signals from each of the following No. 1 and 2 systems: compass, attitude reference, and VOR/ILS navigation. The signals compared are heading (compass), roll and pitch (attitude reference), and localizer and glide slope deviation (VOR/ILS navigation). When an out-of-tolerance condition exists between any of the output signals, the warning system provides a warning indication through actuation of appropriate warning lights. On GJ ALL EXCEPT B-2509 and B-2510, provisions are also provided to indicate an out of tolerance condition for the Low Range Radio Altimeter system if a second unit is installed. On GJ B-2509 and B-2510, ALT comparison is provided.
B.  The system consists of a comparator warning unit and two annunciator panels. The annunciator panels contain the warning lights which light to give a warning indication, and also serve to identify the system malfunctioning. Power to the comparator warning unit is also monitored through the MON PWR warning lights on the annunciator panels which light on loss of ac or dc power to the unit. A test button is provided on the captain's instrument panel and is used to check the operation of the various channels (heading, roll, pitch, localizer deviation, and glide slope deviation) in the system. Location of the components is shown in Fig. 1.
2.  Operation
A.  The system receives power when the COMPARATOR circuit breakers at the circuit breaker panel P6 are closed (Fig. 2). The heading, and the pitch and roll warning channels operate in a similar manner. Taking the heading warning channel as an example: Two differential resolvers are used for the comparison. The comparison signal is obtained from the resolver in the captain's HSI. The other resolver is in the first officer's HSI. From the transmitter portion of the captain's resolver, heading is transferred to the control transformer portion of the first officer's resolver. Here, a comparison is made between heading as sensed by both compass systems. Any variation in heading produces an output through the transmitter portion of the first officer's resolver to the comparator warning unit. This warning signal is fed to a rectifier and filter time delay circuit before being fed to the threshold detector. The filter time delay prevents nuisance warnings during short duration errors. Under normal operation, the threshold detector senses only signals pertaining to a difference in heading of 6 degrees or greater before providing an output to activate the HDG warning lights.
B.  The roll modifier circuit functions to desensitize the heading warning channel when large bank signals are present in order to prevent unnecessary actuation of the HDG lights. This is necessary, due to differences in the dynamic response of the two compass systems when the airplane is banked. This modifying circuit biases the channel so that the greater the degree of bank angle, the greater the error of compass heading required to cause a warning indication.
5C8 
Jun 20/85  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-29-0 Page 1 

K77656
Navigation Warning System Component Location  5C8 
34-29-0  Figure 1  Jun 20/85 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

C.  Roll and pitch signals are monitored in the same manner as heading except the signals come from the ADI. However, the threshold detectors in these circuits provide an output to activate the warning lights when the input signals have a difference of 4 degrees or greater.
D.  When glide slope capture is generated in the computer of the captain's flight director system, a trigger signal is applied which changes the threshold level in the heading, roll and pitch channels. When triggered, the threshold level is reduced from 4 to 3 degrees in pitch and roll and from 6 to 4.5 degrees in heading. The trigger signal, designated GLIDE SLOPE CAPTURE in the diagram, also activates the altimeter channel when altimeter comparison is made to operate.
　
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