(2)  
Setting the display selector switch to DTK SYS will display any existing action code in the single left digit of the right display. (Two right digits of the right display indicate system status). Pressing the HLD pushbutton will replace the single digit action code with the associated two digit malfunction code. Repeated pressing of the HLD pushbutton will display all additional malfunction codes. After all malfunction codes have been displayed, subsequent pressing of the HLD pushbutton will again display the action code.

(3)  
An action code of 1 indicates that system maintenance is required to restore operation. An action code of 2 indicates missing inputs or loss of synchronization. Such faults may be corrected when the proper inputs are either restored or manually entered. An action code of 3 indicates that the RPU output to the autopilot steering may not be correct and should not be used. Normal navigation will take place during action code 3.

(4)  
A list of possible malfunctions with associated malfunction codes, action codes, and corrective actions appears below.

ACTION CODE  MALE CODE  WARN ANNUN  PROBLEM  ACTION 
1  01  FLASHES  RPU COMPUTER CHECK SUM FAILURE  REPLACE RPU 
02  FLASHES  RPU COMPUTER ARITHMETIC CHECK FAILURE  REPLACE RPU 
03  FLASHES  A/D CONVERTER FAILURE  REPLACE RPU 
04  FLASHES  MEMORY ADDRESS FAILURE  REPLACE RPU 
05  FLASHES  DATA CHECK FAILURE  REPLACE RPU 
06  FLASHES  MULTIPLE INPUTS SELECTED  CORRECT DISCRETES 
07  FLASHES  RF/ANTENNA FAILURE  REPLACE RPU/ANTENNA 
2  10  FLASHES  NO SPEED INPUT  PROVIDE INPUT 
11  FLASHES  NO HDG INPUT  PROVIDE INPUT 
12  FLASHES  NEITHER SPEED NOR HDG INPUTS  PROVIDE INPUTS 
13  FLASHES  PWR INTERRUPT FOR MORE THAN 7 SEC  ENTER GMT 
14  FLASHES  NO SYNCHRONIZATION WITH TRANSMITTER AFTER 3 MIN  REPLACE RPU 
15  FLASHES  PRES POSN, GMT, AND/OR DATE NOT ENTERED  ENTER MISSING PARAMETER(S) 
3  17  OFF*  NO ANALOG SYNCHRO EXCITATION 
18  OFF  NO STEERING EXCITATION 
19  OFF  NO SYNCHRO NO. 1 OUTPUT  CHECK DISCRETES 
20  OFF  NO SYNCHRO NO. 2 OUTPUT  AND WIRING. 
21  OFF  NO SYNCHRO NO. 3 OUTPUT  IF CORRECT 
22  OFF  STEERING OUTPUT FAILURE  REPLACE RPU 
23  OFF  NO CROSS TRACK DEV OUTPUT 

*Indication provided by airplane instruments. 
593 
Sep 20/81  34-59-01 
Page 17 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

F.  Omega Stations Status and Signal Quality
(1)  
When the display selector switch is set to STA, eight digits will appear on the CDU display. Each of the digits indicates the status for one of the eight Omega stations. (Stations listed in Fig. 2 are associated with digits 1 thru 8, left to right on the display).

(2)  
The four possible status categories are as follows:

(a)  
Steady station digit -- The station has been selected and is being currently used for Omega navigation.

(b)  
Flashing station digit -- The station is available (sufficient signal quality), but is not being actively used for navigation.

(c)  
Steady Zero -- The station has been deselected by the system due to poor signal quality or bad geography.

(d)  
Flashing Zero -- The station has been manually deselected by the operator.

(3)  
The signal quality of each of the three frequencies can be displayed for any particular station. With the display selector switch in the STA position, the pushbutton (1-8) for the station in question is then pressed. The display will show from left to right, the station number, the 10.2 kHz signal quality index, the 13.6 kHz signal quality index, and the 11.3 kHz signal quality index. All station signal qualities must be 11 or greater for the system to select the station for navigation. Station signal qualities read from 0 to 40. The signal to noise ratio, SNR, is computed by subtracting 20 from the station signal quality index.

(4)  
The operator has the ability to deselect any station which he does not want to be used for navigation. With the display selector switch in the STA position, the STA pushbutton is pressed. The ENT light will come on. The stations, 1-8, to be deselected are entered on the CDU keys. Deselected stations are immediately recognized by a flashing zero in the station status display.
　
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