(5)  
Reselection of the stations is accomplished by pressing the STA pushbutton again and entering stations numbers to be reselected. A flashing zero will no longer be displayed for the reselected stations.

G.  Memory Interrogation
(1)  
Words in memory may be accessed by setting the display selector switch to AUX and the WPT switch to 2. The memory location is entered via the CDU keyboard and appears in the left display. In the right display appears the six digit octal coded word existing in that memory location.

(2)  
The memory is not normally interrogated, except during trouble shooting of a system malfunction. The user will find that five memory words are helpful in fault isolation: an oleo strut switch status word (address 00272), a discretes-validities-reference detectors word (address 25040), a discretes-program pins-power fail discretes word (address 25060), a TAS scaling word (address 00712), and a TAS synchro lap word (address 00710).

34-59-01 Sep 20/81 Page 18
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

 (3)  
Address 00272 - This word displays the landing gear condition as indicated by the oleo strut switch. The oleo strut switch is closed when the airplane is on the ground and the right display shows 17777. When the gear is up, the right display will show 00000.

(4)  
Addresses 25040 and 25060 - Each of these six digit words provide the status for 16 bilevel parameters. The first or most significant digit (MSD) may be a 0 to 1 only and represents the status for a single parameter. The other five digits may be any number from 0 to 7 and each of these digits indicates the status of three parameters. (There are eight possible combinations of three bilevel parameters. Therefore, an octal digit may be used to identify which of these combinations exists and the status of each individual parameter may be determined).

(5)  
The parameters associated with each digit position are listed in Fig. 9 and 10 for addresses 25040 and 25060, respectively. The status of the parameters are shown for the eight possible octal digits.

(6)  
Address 00712 - The true airspeed (TAS) input is stored at this memory location in degrees of synchro rotation. Each of the digit positions is associated with an angle as listed below. The digits themselves are the multipliers. To obtain the synchro displacement, one must sum the products of the digits and the angle associated with the digit positions. For example, if the memory word is 146200, the synchro displacement would be (1 x 1800) + (4 x 22.50) + (6 x 2.810) + (2 x 0.3520) = 2880.

digit position  angle
MSD 1800

2  22.50

3 2.810
4 0.3520
5 0.0440
LSD 0.00550

To calculate TAS in knots, use the conversion for ARINC TAS synchro signals, 10 = 2.77 knots. In the example above, 146200 would indicate a true airspeed of 798 knots.
(7)  Address 00710 - This word is the TAS synchro lap indictor. When the synchro is on its initial lap, it wound be 177777 and when it is on the second lap, the word will be 000000.
5C8 
Jun 20/85  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-59-01 Page 19 

Definitions of Digits Displayed in Address 25040 Word  593 
34-59-01  Figure 9  Sep 20/81 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

593  Definitions of Digits Displayed in Address 25060 Word 
Sep 20/81  Figure 10  34-59-01 
Page 21 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

OMEGA NAVIGATION SYSTEM - TROUBLE SHOOTING
1.  General
A.  A prerequisite for accurately trouble shooting any system is a good knowledge of normal system operation and component locations. Refer to OMEGA navigation system-description and operation for review when required.
B.  The trouble shooting is based on the assumption that electrical power is available and airplane wiring is correct. Trouble shooting steps are based on system control via CDU inputs and observation of CDU displays and RPU monitor indicators.
C.  The relative complexity and the resultant varying times-to-failure of the ONS units indicate that failures will most probably be the result of a malfunction in the RPU; the second most probable cause will be the CDU; and third and last, the antenna. However, trouble shooting where ONS inputs appear to be involved, or where an ONS hard failure is not indicated (RPU BITE indicator not set) should include a check of airplane wiring, particularly wiring at program discrete pins. In addition, information supplied by codes displayed on the CDU should be used to verify a proposed unit replacement. However, in most instances trouble shooting will be a "replace with known-good unit" procedure starting with the RPU followed by the CDU, and lastly the antenna.
　
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