DOC AIRBUS | AMM A320FAUTOTHRUST ENGAGEMENT - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
The A/THR function can be engaged in three different ways:
The ALPHA FLOOR activation is not possible in the engine stopped and flaps extended configuration.
** ON A/C NOT FOR ALL The A/THR function can be engaged in three different ways:
- When the A/THR pushbutton switch on the FCU is pushed in, with aircraft on the ground and engines stopped or in flight at an altitude higher than 100 feet (except in LAND TRACK phase)
- Automatically further to the engagement of the AP/FD TAKE OFF or GO AROUND modes
- Automatically if the ALPHA FLOOR condition elaborated in the FAC is present and if the altitude is higher than 100 feet.
The ALPHA FLOOR activation is not possible in the engine stopped and flaps extended configuration.
2. System Description
A. FMGC Priorities at FCU Level
The FMGC which has priority, depending on the AP/FD and the A/THR engagement, controls the engine thrust.
The logic below defines the FMGC which has priority:
The FMGC which has priority, depending on the AP/FD and the A/THR engagement, controls the engine thrust.
The logic below defines the FMGC which has priority:
| ------------------------------------------------------------------------------- |
| ! AP engagement ! FD engagement ! A/THR engagement ! FMGC ! |
| !--------------------!---------------------!---------------------! having ! |
| ! FMGC1 ! FMGC2 ! FMGC1 ! FMGC2 ! FMGC1 ! FMGC2 ! priority ! |
| !---------!----------!----------!----------!----------!----------!------------! |
| ! 1 ! - ! - ! - ! - ! - ! 1 ! |
| ! 0 ! 1 ! - ! - ! - ! - ! 2 ! |
| ! 0 ! 0 ! 1 ! - ! - ! - ! 1 ! |
| ! 0 ! 0 ! 0 ! 1 ! - ! - ! 2 ! |
| ! 0 ! 0 ! 0 ! 0 ! 1 ! - ! 1 ! |
| ! 0 ! 0 ! 0 ! 0 ! 0 ! 1 ! 2 ! |
| ------------------------------------------------------------------------------- |
- : indifferent
A/THR Engage Logic(1) Disengaged
In this case:
In this case:
- the engines are controlled by the throttle control levers,
- on the FCU, the A/THR pushbutton switch is off,
- the FMA does not display the A/THR engagement status and the A/THR modes.
(2) Engaged
When the A/THR engage logic conditions are present, the A/THR can be engaged.
The A/THR engaged can be:
When the A/THR engage logic conditions are present, the A/THR can be engaged.
The A/THR engaged can be:
(a) Active when the two throttle control levers are in the A/THR active area.
In this case:
In this case:
- the autothrust system controls the engines,
- on the FCU, the A/THR pushbutton switch is on,
- the FMA displays A/THR in white in the right column and one A/THR mode in the left column.
(b) Not active, if both throttle control levers are above CL gate or one throttle control lever above MCT gate.
In this case:
In this case:
- the throttle control levers control the two engines,
- the A/THR pushbutton switch is on,
- the FMA displays A/THR in cyan in the right column and the thrust setting in the left column.
C. A/THR Engage and Disengage Logic
The A/THR can only be engaged when all the necessary conditions are present and if there is a request for engagement (pilot action or automatic).
The A/THR can only be engaged when all the necessary conditions are present and if there is a request for engagement (pilot action or automatic).
(1) Required engagement conditions
Two conditions are required to make the engagement possible:
Two conditions are required to make the engagement possible:
(a) AP/FD/A/THR common condition
This condition results from the monitoring functions below:
This condition results from the monitoring functions below:
- monitoring of the validity of the ADIRS input parameters (two ADIRS must be valid). This monitoring consists in a check of the SSM and refreshment period.
The monitoring of the main parameters is made by vote or comparison. - monitoring of LGCIUs parameters. This monitoring is made in the FAC which informs the FMGC of the validity of the LGCIU parameters. One LGCIU at least must be healthy. This condition is not required at landing or during go around.
- internal monitoring of the guidance portion healthy.
- internal monitoring of the management portion healthy. This condition is not required at landing or during go around.
NOTE: The monitoring functions common to the AP/FD and A/THR are described in 22-11-00 AP/FD Engagement.
(b) A/THR specific condition
This condition specific to A/THR includes the conditions below:
This condition specific to A/THR includes the conditions below:
- A/THR must be either in the manual speed or in the auto speed control mode (Ref. 22-10-00 AP/FD)
- the two ECUs/EECs must be healthy
- the FCU must be healthy
- no discrepancy between the N1/EPR target computed in the FMGC and the N1/EPR feedback from each ECU/EEC when the A/THR is active
- the various parameters used in the flight envelope protection such as VLS, VMAX, etc. must be healthy
- no action on one of the two A/THR instinctive disconnect pushbutton switches lasts more than 15s.
(2) Disengagement conditions
The presence of one of the conditions below causes the disengagement of the A/THR:
The presence of one of the conditions below causes the disengagement of the A/THR:
(a) Loss of one common or specific condition described above
(loss of the ADIRS or FAC parameter validity does not cause A/THR disengagement as long as the Alpha floor protection is active).
(loss of the ADIRS or FAC parameter validity does not cause A/THR disengagement as long as the Alpha floor protection is active).
(b) "Synchronization between FMGC" condition.
This condition forces the disengagement if the A/THR function on the opposite FMGC is disengaged and on condition that this FMGC has priority.
This condition forces the disengagement if the A/THR function on the opposite FMGC is disengaged and on condition that this FMGC has priority.
(c) Action on the A/THR pushbutton switch, with the A/THR function already engaged. This action has no effect in LAND TRACK mode.
(d) Action on one of the A/THR instinctive disconnect pushbutton switches.
(e) AP/FD loss condition i.e. total loss of AP/FD below 100ft with the RETARD mode not engaged.
(f) Go around condition i.e. one throttle control lever is placed in the non active area (> MCT) below 100ft without engagement of the GO AROUND mode on the AP/FD.
(g) One engine start on the ground.
(h) Both throttle control levers placed in the IDLE position.
(i) ECU/EEC autothrust control feedback i.e. the A/THR being active at level of the FMGCs, one of the two ECUs/EECs indicates that it is not in autothrust control mode.
(j) both throttle control levers placed in the REVERSE position.
(3) A/THR ACTIVE logic
After engagement, the A/THR is active if:
After engagement, the A/THR is active if:
- the two throttle control levers are between IDLE and CL (CL included)
- one throttle control lever is between IDLE and CL (including CL), and the other is between IDLE and MCT (including MCT) with FLEX TO limit mode not selected
- the Alpha floor protection is active whatever the position of the throttle control levers.
D. Realization of the Engage or Disengage Logic
The engagement of the A/THR function is duplicated in each FMGC at level of the guidance, command and monitoring channels.
The A/THR ENGD signal that the ECUs/EECs receive via the FCU and the EIUs comes from the command channel. The A/THR ENGD C and M discrete outputs used in the A/THR instinctive disconnect circuit (Ref. Para. 2.E.) take into account the result of computation of the command and monitoring channels.
The Alpha floor condition from the FACs is used in the command and monitoring processors for the elaboration of the Alpha floor protection. This causes the automatic engagement of the A/THR.
When both FACs are healthy, the logic condition makes engagement of the Alpha floor protection only when both FACs deliver the Alpha floor condition.
If one FAC is not healty and the Alpha Floor condition is present, the protection is achieved by the other healty FAC.
A comparison between the command and monitoring channels at level of this protection is performed.
If there is a difference between these channels, the A/THR function is disengaged.
The comparison between the computed N1/EPR target and the N1/EPR target feedback sent by each ECU/EEC is performed at level of the command and monitoring channels of each FMGC.
Any excessive deviation is taken into account at level of the A/THR engage logic of the command and monitoring channels.
The engagement of the A/THR function is duplicated in each FMGC at level of the guidance, command and monitoring channels.
The A/THR ENGD signal that the ECUs/EECs receive via the FCU and the EIUs comes from the command channel. The A/THR ENGD C and M discrete outputs used in the A/THR instinctive disconnect circuit (Ref. Para. 2.E.) take into account the result of computation of the command and monitoring channels.
The Alpha floor condition from the FACs is used in the command and monitoring processors for the elaboration of the Alpha floor protection. This causes the automatic engagement of the A/THR.
When both FACs are healthy, the logic condition makes engagement of the Alpha floor protection only when both FACs deliver the Alpha floor condition.
If one FAC is not healty and the Alpha Floor condition is present, the protection is achieved by the other healty FAC.
A comparison between the command and monitoring channels at level of this protection is performed.
If there is a difference between these channels, the A/THR function is disengaged.
The comparison between the computed N1/EPR target and the N1/EPR target feedback sent by each ECU/EEC is performed at level of the command and monitoring channels of each FMGC.
Any excessive deviation is taken into account at level of the A/THR engage logic of the command and monitoring channels.
E. Isolation of the Engines from the A/THR System
The engine control is no longer dependent on the throttle control levers when the conditions below (elaborated by the FMGC and transmitted to the ECU) are met:
This is done through the wired discretes that the ECU receives directly.
This device permits to get rid of any failure downstream of the FMGC which might cause an untimely engagement of the A/THR function.
At level of the A/THR engage logic performed by the FMGC, an action on one of the two A/THR instinctive disconnect pushbutton switches for more than 15 s. inhibits any engagement of the A/THR function, whatever the reason (A/THR pushbutton switch on the FCU, Alpha floor protection etc.) (Ref. Para. 2.B.).
A similar protection is available at level of each ECU/EEC. Action on one of the two A/THR instinctive disconnect pushbutton switches for more than 15 s. inhibits operation of each ECU/EEC in autothrust control mode.
The engine control is no longer dependent on the throttle control levers when the conditions below (elaborated by the FMGC and transmitted to the ECU) are met:
- A/THR ENGD
- A/THR ACT
- TARGET N1/EPR VALID
- throttle control lever in the area which authorizes the autothrust control or Alpha floor protection active.
This is done through the wired discretes that the ECU receives directly.
This device permits to get rid of any failure downstream of the FMGC which might cause an untimely engagement of the A/THR function.
At level of the A/THR engage logic performed by the FMGC, an action on one of the two A/THR instinctive disconnect pushbutton switches for more than 15 s. inhibits any engagement of the A/THR function, whatever the reason (A/THR pushbutton switch on the FCU, Alpha floor protection etc.) (Ref. Para. 2.B.).
A similar protection is available at level of each ECU/EEC. Action on one of the two A/THR instinctive disconnect pushbutton switches for more than 15 s. inhibits operation of each ECU/EEC in autothrust control mode.
(1) Presentation
Upon disengagement of the A/THR and in certain flight phases, the FWCs elaborate the warnings below:
Upon disengagement of the A/THR and in certain flight phases, the FWCs elaborate the warnings below:
(a) Illumination of the MASTER CAUT lights in amber on the glareshield.
(b) Display of A/THR OFF amber message in the memo area of the upper display unit of the ECAM system when the disengagement is due to use of the instinctive disconnect pushbutton switch,
display of AUTO FLT-A/THR OFF amber message in the warning area of the upper display unit of the ECAM system when the disengagement is not due to use of the instinctive disconnect pushbutton switch.
display of AUTO FLT-A/THR OFF amber message in the warning area of the upper display unit of the ECAM system when the disengagement is not due to use of the instinctive disconnect pushbutton switch.
(c) Aural warning (single chime).
(d) THR LK message flashing on the two PFDs if, upon disengagement, the thrust is frozen on at least one engine (THR LK = thrust lock).
In addition, the A/THR engage pushbutton switch goes off on the FCU and the A/THR indication (white or cyan) disappears on the PFD.
If energy management functions are activated, memothrust situation is indicated by:
In addition, the A/THR engage pushbutton switch goes off on the FCU and the A/THR indication (white or cyan) disappears on the PFD.
If energy management functions are activated, memothrust situation is indicated by:
- amber ENGINE THRUST LOCKED flashing message on Upper ECAM DU
- repetitive single chime and MASTER CAUT light on.
THR LEVERS ..... MOVE message is repeated on upper ECAM DU.
(e) Throttle control levers below CL warning
If energy management functions are activated, if both throttle control levers are set below the CL gate (or one throttle control lever below MCT gate in case of engine failure), the following warnings are provided:
If energy management functions are activated, if both throttle control levers are set below the CL gate (or one throttle control lever below MCT gate in case of engine failure), the following warnings are provided:
- amber AUTO FLT A/THR LIMITED flashing message on upper ECAM DU
- repetitive single chime
- MASTER CAUT light on.
THR LEVERS ..... MOVE message is repeated on upper ECAM DU.
(2) Conditions for clearing of A/THR warnings
There are several causes of A/THR disengagement (Ref. Para. 2.C. (2)).
There are several causes of A/THR disengagement (Ref. Para. 2.C. (2)).
(a) Upon disengagement of the A/THR through the throttle control levers in the IDLE position below 50 ft., the FWC generates no warning.
(b) Upon intentional disengagement of the A/THR through action on one of the two instinctive disconnect pushbutton switches or through the throttle control levers in the IDLE position above 50 ft., the warnings are automatically cancelled:
- the MASTER CAUT light goes off after 3s
- the A/THR OFF message disappears after 9s.
NOTE: The two warnings above can be cancelled faster by pilot through action on the MASTER CAUT light or on one of the two instinctive disconnect pushbutton switches.
(c) Upon disengagement of the A/THR due to one of the other causes, the two visual warnings can be cancelled:
- through action on one of the CLR keys located on the ECAM control panel
- through action on the MASTER CAUT light
- through action on one of the two instinctive disconnect pushbutton switches.
(3) Elaboration of A/THR warning
Each FWC elaborates the A/THR warning and uses the signals below:
The 3 DMCs convert these codes into specific codes which are sent to the PFDs and to the upper display unit of the ECAM system through the DSDL bus.
In normal operation:
Each FWC elaborates the A/THR warning and uses the signals below:
- A/THR engagement (boolean from the FMGC via the FCU)
- position of the throttle control levers from the ECUs/EECs.
The 3 DMCs convert these codes into specific codes which are sent to the PFDs and to the upper display unit of the ECAM system through the DSDL bus.
In normal operation:
- the DMC1 drives the PFD1 and the upper display unit of the ECAM system,
- the DMC2 drives the PFD2.
In case of DMC1 or DMC2 failure, the crew can switch over to the DMC3 through the use of the EIS DMC selector switch.
The DMC3 replaces totally the failed DMC.