Verification of FAC ARINC Transmissions
 Figure 003
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 -The INTERNAL MONITORING signal either directly or through an oscillation detector to take into account the oscillations of the software which cause switching from good to bad status alternately.
 (b) Activation to good status
 This is achieved:

 -At power rise of the computer if the watchdog, EXPT and INTERNAL MONITORING signals are good
 -Through unlatching by action on the engagement pushbutton
 switch in flight.
 The latter action resets:

 -
The watchdog

 -
The microprocessor. The action which is taken into account is the disengagement of the FAC. Therefore, when the FAULT legend on the FLT CTL/FAC pushbutton switch comes on, the pilot will attempt to re-initiate the computation by disengaging the system. At re-engagement, the system will be at the ON status if the reset has been effective.

 (3) Monitoring of the digital section The real-time monitor ensures the correct operation of the program through the execution of tasks. A watchdog hardware circuit monitors this real-time monitor. The content of the program is checked during the tests at power rise (check sum, signature).
 (a)
 Real-time monitor This monitor ensures the real-time monitoring of the program execution. To do this, it initiates the application through the activation of tasks. It checks each task for discrepancies (exceeded calculating-time limit):

 -By confirmation upon n consecutive discrepancies
 -Through oscillation detectors within a determined time. The monitoring of all the tasks is grouped on an AND logic which acts on the FAC HEALTHY hardware logic (boolean BRLTIME) through a watchdog.

 (b)
 Monitoring of the exceptions
 An exception results from an instruction which cannot be
 performed normally for these reasons:

 -Either it does not follow the rules of the memory protection (protected mode of the CPU 80286)
 -
Or it leads to an erratic result

 -
Or the instruction itself is garbled (for example : dividing by zero)

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 All the types of exceptions (fifteen approximately) are grouped
 in every task.
 The boolean BEXPT gathers all the exception monitoring functions.
 This boolean acts on the FAC HEALTHY logic at the level of:

 -
The watchdog for its activation

 -
The logic.

 C. Monitoring of Peripherals
 (1) Monitoring of ADIRS data
 (a)
 General Some data from the ADIRS have a critical role in the architecture of the FAC. Specific monitoring functions are integrated for these parameters:

 -Yaw rate (yaw damper and engine failure recovery)
 -Lateral acceleration (engine failure recovery)
 -Corrected airspeed (rudder travel limiting)
 -Angle-of-attack (calculation of characteristic speeds).

 (b)
 Principle The monitoring functions performed on the ADC and IRS labels must permit the elimination of the affected source.

 1_ Failures detected from the processing of the status matrices:
 These failures are not latched.
 2_ Failures not detected by self-test from:
 - A 3 IRS-source vote for the yaw rate and the lateral
 acceleration
 - A two-by-two comparison for the corrected airspeed
 - A 3 ADC-source vote for the angle-of-attack.
 These failures are latched.
 The table given below
 (Ref. Fig. 004)
 gives the consequences of the ADIRS failures on the FAC
 functions.
 NOTE : In order to get a correct cross comparison of____
 angle-of-attack in case of important side-slip,
 angle-of-attack No.3 is corrected by side-slip
 compensation.
 The principle of recognition and elimination of the source is:
 - Corrected airspeed
 (Ref. Fig. 005, 006)

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 Reconfiguration Table
 Figure 004
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 ADC Processing
 Figure 005
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