W DOC AIRBUS | AMM A320F

FAC: ELECTRICAL AND HYDRAULIC POWER SUPPLY - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL
1. Electrical Power Supply
A. 28VDC Power Supply
F 28VDC Power Supply - Block Diagram ** ON A/C NOT FOR ALL
The FAC1 is supplied with 28VDC:
  • From the 28VDC ESS BUS 4PP through the 28VDC ESS BUS/SHED 801PP via 10A circuit breaker 5CC1.
The FAC2 is supplied with 28VDC:
  • From the 28VDC BUS 2 2PP through the 28VDC BUS 2 206PP via 10A circuit breaker 5CC2.
The 28VDC power supply generates:
  • All the voltages associated with internal computation (+ 5VDC, + 15VDC and - 15VDC)
  • The logic processing voltages (discretes, relays, etc.).
All these voltages derived from the 28V power are monitored by the FAC in the command and monitoring channels.
The FAC1 is supplied with 28VDC:
  • From the 28VDC ESS BUS 4PP through the 28VDC ESS BUS/SHED 801PP via 10A circuit breaker 5CC1.
  • Through the 28VDC HOT BUS 701PP via 10A circuit breaker 16CC. When the essential busbar is lost, this power supply is maintained during 10 seconds thanks to a temporized relay.
The FAC2 is supplied with 28VDC:
  • From the 28VDC BUS 2 2PP through the 28VDC BUS 2 206PP via 10A circuit breaker 5CC2.
The 28VDC power supply generates:
  • All the voltages associated with internal computation (+ 5VDC, + 15VDC and - 15VDC)
  • The logic processing voltages (discretes, relays, etc.).
All these voltages derived from the 28V power are monitored by the FAC in the command and monitoring channels.
B. 26V/400 Hz Power Supply
F 26VAC Power Supply - Block Diagram
The rotary variable differential-transducers and the linear variable differential-transducers associated with the FAC1 are supplied with 26V/400 Hz:
  • From the 115VAC ESS BUS 4XP through the 26VAC ESS BUS 431XP.A via 3A circuit breaker 14CC1.
The components associated with the FAC2 are supplied with 26V/400 Hz:
  • From the 115VAC BUS 2 2XP through the 26VAC BUS 2 231XP-A via 3A circuit breaker 14CC2.
C. Internal Power Supply
F FAC - Internal Power Supply
(1) Behaviour of the FAC under 28V transients
Cutoffs of the 28V power supply may occur for periods lasting up to 200 ms especially in case of engine failure.
The system is designed as follows (power supply and safeguard):
(a) Cutoffs less than or equal to 10 ms.
The operation remains normal, without safeguard, as the power supply absorbs this cutoff. In this case, the solenoid valves are not energized which has no impact (de-energizing time of the solenoid valves = 35 ms).
(b) Cutoffs less than 200 ms.
The normal operation is interrupted (return to synchro mode) and the context is safeguarded (computation, ARINC transmission and reception).
In this configuration, the changeover order is transmitted and the external validations are interrupted (solenoid valves, validation of servo-actuator, etc.).
At power restoration, the considered system is re-activated (hence possibility of changeover) with the safeguard context after temporary inhibition of the power comparators.
(c) Cutoffs greater than 200 ms.
1 In-flight cutoffs
These are long cutoffs. Normal operation is interrupted. The context (ARINC and computation) is lost (transmissions interrupted).
The FAULT legend is on and the changeover order is given.
At normal power restoration:
  • The content of the computer is reset
  • The system returns to synchro mode. The FAULT legend remains on.
Pilot action on the pushbutton switch is required to re-engage the system.
2 Cutoffs on the ground
During long cutoffs on the ground, the operation is different to avoid any re-engagement action by the pilot.
At normal power restoration:
  • The failure is cleared (FAULT legend off)
  • The system takes over from a null order.
If the cutoff exceeds 5 s, the safety tests are re-initiated.
This operation is acceptable in the event of engine failure if no untimely significant movement of control surfaces is induced.
As the FAC cannot keep the solenoid valves of the yaw damper servo-actuator energized, a centering of the rudder to the initial position can happen for any 28V cutoff greater than 35 ms (if only one FAC is available).
The table given below reports the FAC behaviour under 28V cutoffs:
-------------------------------------------------------------------------------
! 28V CUTOFFS ! FAC SAFEGUARD ! FAC MODE ! COMMENTS !
!--------------!-----------------------!--------------!-----------------------!
! Less than !- Context undisturbed !- No change- !- FAULT legend off !
! 10 ms !- Servo-actuator vali- ! over !- Re-engagement not !
! ! dation interrupted ! ! required !
! ! ! !- Operation in normal !
! ! ! ! function !
!--------------!-----------------------!--------------!-----------------------!
! Less than !- Context safeguarded !- Changeover !- FAULT legend on !
! 200 ms !- Servo-actuator vali- !- Synchro mode! during cutoff !
! ! dation interrupted ! during cut- !- Re-engagement not !
! !- Temporary inhibition ! off ! required !
! ! of power comparators !- Return of !- Normal function with !
! ! at restoration ! priority at ! possible switching !
! ! ! power res- ! from FAC1 to FAC2 !
! ! ! toration ! and return to FAC1. !
!--------------!-----------------------!--------------!-----------------------!
! IN FLIGHT !- Context lost with !- Changeover !- FAULT legend remains !
! Greater than ! re-activation and !- Synchro mode! on after power res- !
! 200 ms ! reset ! at power ! toration !
! !- Servo-actuator vali- ! restoration !- Re-engagement possi- !
! ! dation interrupted !- No return ! ble after power res- !
! ! ! of priority ! toration !
! ! ! !- The other FAC ful- !
! ! ! ! fills the function !
! ! ! ! and the pilot can !
! ! ! ! select this FAC !
!--------------!-----------------------!--------------!-----------------------!
! ON THE GROUND!- Context lost with !- Changeover !- FAULT legend goes !
! Greater than ! re-activation and !- Synchro mode! off after power res- !
! 200 ms ! reset ! at power ! toration !
! !- Servo-actuator vali- ! restoration !- Re-engagement not !
! ! dation interrupted ! and re-en- ! required !
! ! ! gagement of !- Return to this FAC !
! ! ! synchro per-! after synchroniza- !
! ! ! formed ! tion !
-------------------------------------------------------------------------------

(2) Behaviour of the FAC under 26V/400 Hz cutoffs
F Behaviour of the FAC under 26VAC/400 Hz Cutoff (on 1 channel)
The 26V/400 Hz is only used to energize the position feedback transducers. Loss of the transducer 26V is detected by monitoring the VR value through comparison with a VRTH value (theoretical VR).
This second detection also enables to monitor the 26V cutoff:
The 26V cutoff is effective when the three VR voltages (yaw damper, rudder trim and RTL) are simultaneously lower than 75% of their theoretical values. If only one or two VR voltages are lower than this threshold, the 26V cutoff is not considered.
  • First case : 26V cutoff lower than 200 ms.
    The three actuators remain engaged but the three slaving orders are inhibited by this software monitoring (INHIBITION ORDER). This signal cancels the three current outputs of the FAC during the cutoff. The transducer monitoring is inhibited one second after the beginning of the cutoff to avoid untimely disconnections at 26V restoration.
  • Second case : 26V cutoff greater than 200 ms.
    The three actuators are disengaged and there is a changeover on the three channels.
** ON A/C NOT FOR ALL
2. Hydraulic Power Supply
F Yaw Damper Servo-Actuator - Hydraulic Power Supply
A. The electro-hydraulic yaw damper servo-actuator uses the aircraft hydraulic power supply. The servo-actuator comprises two independent motors which can drive the output shaft and therefore the rudder.
The servo-actuator 1 associated with the FAC1 is powered by the Green hydraulic system.
The servo-actuator 2 associated with the FAC2 is powered by the Yellow hydraulic system.
As no internal pressurization contact is provided in the servo-actuator, any possible absence of pressure is detected at the level of the consequences (non slaving).
A signal external to the servo-actuator is available.
[Rev.10 from 2021] 2026.04.01 05:13:57 UTC
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