3. Operation
_________
 A. Connection with FLT CTL/FAC Pushbutton Switches (Ref. Fig. 001) Each FAC is associated with an engagement pushbutton switch located on the FLT CTL panel, on the overhead panel. This pushbutton switch serves for:
 -
The engagement or the disengagement of all the FAC functions: . Engagement status : no indication on the pushbutton switch . Disengagement status : the OFF legend is on

 -
The indication of FAC failures with the FAULT legend. This authorizes a pilot action (FAULT/OFF) to reset the digital section of the FAC. If the action is operative, the FAULT legend goes off and the system can be re-engaged.

 Therefore, in normal operation the legends are off.
 In abnormal operation, these indications are given:

 -Computer not energized or not installed:
 . FAULT legend on ; ECAM warning.

 -FAC failures specific to one function:
 . FAULT legend off ; ECAM warning.

 -Common FAC failures which can be reset: . FAULT legend on with possible reset by the pilot ECAM warning.
 -Power-supply transient failures:
 . FAULT legend on with possible reset by the pilot.

 -FAC failures on the ground with engines shut down: . FAULT legend with automatic reset at failure suppression.
 B. Global Internal Monitoring of the Computer (Ref. Fig. 002) The correct operation of the computer (acquisition, digital section, correct running of the program, transmission, etc.) is checked from:
 -
A boolean signal INTERNAL MONITORING generated by the software. This signal takes into account all the monitoring functions of the channel

 -
A FAC HEALTHY discrete signal used as a condition necessary for: . The effective engagement of the FAC functions, . The validation of the FAC data for the users.

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 FAC Engagement Principle
 Figure 001
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 Monitoring of the Computer
 Figure 002
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 (1)
 INTERNAL MONITORING signal This signal is generated from the signals given below:

 -Internal power-supply monitoring
 -
Monitoring of the correct execution of the safety test of the digital section.

 -
Monitoring of the ARINC transmission: . Through wrap-around of the main bus on the monitoring channel by comparison of the received discrete word 274 with the discrete word 274 generated in the monitoring channel (Ref. Fig. 003)

 -
Monitoring of the ARINC acquisition through verification of the automaton which organizes the management of the acquisition

 -Verification of the digital section by taking into account: . The comparator between voters of the yaw damper . The comparator between speed computations. As these comparators monitor the command and the monitoring algorithms, a dissymmetry between these computations implies a failure in the digital section.

 (2)
 FAC HEALTHY signal This hard-wired signal is used to:

 -Illuminate the FAULT legend of the FLT CTL/FAC pushbutton switches
 -Validate the information of the main bus of the FAC: . Through the acquisition of this discrete by the users. Through setting of the transmitted labels to F/W
 -Authorize the engagement of the functions (use of the FAC HEALTHY
 signal wrapped around to generate the changeover signals).
 This signal is dependent upon:

 -
The INTERNAL MONITORING signal

 -
The nosewheel signal to avoid latching of possible failures on the ground

 -
The watchdog signal which monitors the correct execution of the software operations

 -
The REAL TIME HLTY signal which is the real-time monitoring signal of the application software (Ref. para. (3)a.)

 -
The EXPT signal which is an exception procedure signal (Ref. para.

 (3)b.)
 The FAC HEALTHY signal is latched in flight only.
 It is activated as follows:

 (a) Activation to fault status
 This is achieved by:

 -
The watchdog signal

 -
The exception signal

 -
The FAC HEALTHY signal generated by the opposite side (C or M)

 -
The LPF signal : this signal is activated by the power supply block upon long cutoff (t more than or equal to 200 ms)

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