AUTOTHRUST MODES - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General
The A/THR modes which enable to perform the automatic thrust control are SPD/MACH, THRUST and RETARD. These modes are activated automatically as a function of the AP or FD - selected longitudinal modes.

** ON A/C NOT FOR ALL

2. System Description

A. Engage Logic of A/THR Modes

Activation of A/THR Mode according to AP/FD Modes

The choice of A/THR mode according to the AP/FD active mode or sub-mode is shown in the table below:

-------------------------------------------------------------------------------

! AP/FD ! A/THR Mode ! Remarks !

! Mode ! Sub-Mode ! ! !

!------------------!------------------!------------------!--------------------!

! Takeoff-Go Around! - ! Thrust ! If A/THR is not !

! ! ! ! active the takeoff !

! ! ! ! or go-around thrust!

! ! ! ! is directly !

! ! ! ! controlled by the !

! ! ! ! ECUs/EECs. !

!------------------!------------------!------------------!--------------------!

! V/S-FPA ! V/S-FPA ! SPD/MACH ! !

! !------------------!------------------!--------------------!

! ! ALT ! SPD/MACH ! !

!------------------!------------------!------------------!--------------------!

! ALT ACQUIRE ! - ! SPD/MACH ! !

!------------------!------------------!------------------!--------------------!

! ALT ! ALT ! SPD/MACH ! !

! !------------------!------------------!--------------------!

! ! V/S ! SPD/MACH ! !

!------------------!------------------!------------------!--------------------!

! CLB-DES ! SPEED/THRUST ! THRUST ! !

! ! V.PATH/SPEED ! SPD/MACH ! !

! ! FPA/SPEED ! SPD/MACH ! !

! ! V/S/SPEED ! SPD/MACH ! !

! ! V. PATH/THRUST ! THRUST ! !

!------------------!------------------!------------------!--------------------!

! EXPEDITE ! - ! THRUST ! !

!------------------!------------------!------------------!--------------------!

! OPEN CLB ! - ! THRUST ! !

! OPEN DES ! ! ! !

!------------------!------------------!------------------!--------------------!

! ! ! ! _ !

! FINAL DESCENT ! ! SPD ! _! R.NAV APPROACH !

! GLIDE CAPT ! ! SPD ! ! !

! GLIDE TRACK ! ! SPD ! ! ILS APPROACH !

! LAND TRACK ! ! SPD ! _! !

-------------------------------------------------------------------------------

The RETARD mode is available only in automatic landing i.e. the AP is engaged in LAND TRACK mode. Then the RETARD mode is engaged when the radio altitude becomes lower than 40 ft.
If the AP is disengaged during flare-out before touchdown, the RETARD mode is replaced by the SPD/MACH mode.
On ground, this logic is not active and the RETARD mode is kept.
In automatic landing, the FWC auto call out delivers a RETARD message at 10 ft.. The pilot then moves the throttle control levers to the IDLE position to take manual control of the thrust for the landing. With the A/THR engaged but not in the automatic landing conditions, this message is delivered at 20 ft.
If no longitudinal mode is active on the AP/FD, the A/THR mode selected is SPD/MACH.
When the AP and FD are not engaged, the A/THR mode selected is SPD/MACH on condition that the RETARD mode is not already active.
The RETARD mode is kept if the AP/FD is disengaged.
As for the AP/FD modes, the A/THR modes of the FMGC which has no priority are synchronized on the A/THR modes of the FMGC which has priority.

B. Alpha Floor Protection

Alpha Floor Protection

When the angle of attack reaches a limit value dependent on the configuration and longitudinal wind gradient, the FAC sends an order to the FMGC.
This order is taken into account in the FMGC as soon as the landing gear shock absorbers are extended at takeoff and up 100 ft at landing.
This causes:

the engagement of the A/THR function
the activation of the Alpha FLoor Protection of the A/THR which commands max. thrust to the engines whatever the AP/FD mode engaged.

The activation logic of the Alpha Floor Protection is not synchronized between the two FMGCs.
The Alpha Floor can only be cancelled through the disengagement of the A/THR function.

C. A/THR Control Laws and Associated Reference Data
The A/THR laws available are:

fixed thrust hold (THRUST law)
speed or MACH hold (SPD/MACH law of A/THR).

(1) THRUST law
This law is selected when the A/THR operates in THRUST or RETARD mode or when the Alpha floor protection is active.
The THRUST law permits to command to the two engines a fixed thrust which can be:

N1/EPR LIM: limit thrust (calculated by the FADECs according to the throttle control levers position) when the AP/FD mode gives a climb order
N1/EPR IDLE: reduced thrust when AP/FD mode gives a descent order or RETARD mode engaged
N1/EPR MAX : max. thrust whatever the position of the throttle control levers when the Alpha Floor Protection is active.
This thrust corresponds to the thrust that would be obtained when the two throttle control levers are in TO/GA position.
FM N1/EPR target: thrust that the flight management section calculates when it ensures the longitudinal guidance of the aircraft.

(2) SPD/MACH law

SPD/MACH Law

This law is selected when the A/THR operates in SPD/MACH mode on condition that the Alpha Floor Protection is not active.
Depending on the logic for MACH control selection and selected or managed speed control (Ref. 22-10-00-AP/FD), the SPD/MACH law enables to acquire and hold:

either the speed displayed on the FCU when the selected control of the speed is active
or the Mach on the FCU when the Mach control is selected and the selected speed control is active
or a speed chosen by the managed speed control
or a Mach chosen by the managed speed control when the Mach control is active.

Depending on the target speed or Mach, a precommand N1/EPR is calculated:

from an aerodynamic model
from a simplified engine model independent from the flight management section.

A direct channel and an integrated channel permit to hold the speed or Mach and compensate the computation error of the precommand N1/EPR
The VLS and VMAX limit the target speed and Mach.
A load factor precommand in V/S and ALT ACQ mode permits to minimize the speed variation during dynamic maneuvers which involve climb or descent at constant speed.

(3) Elaboration of N1/EPR controlled by the A/THR

A/THR Basic Loop

To perform the automatic thrust control, the A/THR transmits to the FADECs the rate which must be commanded to the engines: N1/EPR target.
The N1/EPR target is elaborated in the basic loop of the A/THR.
When the A/THR is not active, the N1/EPR target which is transmitted is the recopy of the N1 corresponding to the throttle control lever in the most advanced position.
When the A/THR is activated, the basic loop permits to pass smoothly from N1/EPR TLA to the N1/EPR elaborated by the THRUST or SPD/MACH control laws.

D. Realization of Control Laws and Modes (Ref. 22-31-00)

SPD/MACH Law

The processors on the command side of the FMGC calculate the mode logic, control laws, the A/THR basic loop and the precommand of the SPEED/MACH mode.
The command and monitor sides calculate the Alpha Floor Protection logic.
The comparison of the results is taken into account at level of the FMGC internal monitoring.

E. Indications on the FMA

A/THR Indications ** ON A/C NOT FOR ALL

During A/THR operation, different messages are displayed on the FMA. The FMA is located on the upper section of the Primary Flight Display (PFD).
This area is divided into 5 columns of 3 lines each, on which several FMGC operations are displayed.
The right column shows the engagement status.
The left column shows different A/THR modes and actions required.

A/THR Indications ** ON A/C NOT FOR ALL

(1) A/THR engagement status
The A/THR message is displayed on the 3rd line of the right column in one of the two colors below.

(a) White
When the A/THR is engaged and active: the autothrust system controls the engines.

(b) Cyan
When the A/THR is engaged but not active: the two engines are controlled by the position of the throttle control levers and by the ECUs/EECs.

(2) A/THR modes
The A/THR modes are displayed on the left column if the A/THR is engaged.
Three different types of indications are displayed with appropriate colors.

(a) On the first line, green messages or 3 green dashes

1 Green message when:

the A/THR function is overriden by a throttle control lever positioned beyond the MCT gate
the AP/FD active modes are: takeoff, landing, go around, V/S or FPA, EXPED, OPEN CLB, OPEN DES
the thrust is not consistent with the engine configuration (single-engine or not).

2 Three green dashes when:

the autothrust is active and when the thrust is consistent with the engine configuration and flight phase (only cruise phase).

(b) On the second line, amber flashing messages for action to be taken by the crew on the throttle control levers.

(3) Message meaning

(a) On the FMA first line:

TO/GA: A/THR is engaged, one throttle control lever at least in TO/GA position, the thrust is under the control of the ECUs/EECs.
FLX 50: A/THR is engaged. The takeoff is performed in FLX TO with a FLEX TO temperature (50 deg. C for example), selected on the MCDUs. One throttle control lever at least is in FLX TO/MCT position, the other one is in the same position or below.
MCT: A/THR is engaged in thrust mode and the most advanced throttle control lever is in the MCT position.
CLB: A/THR is engaged in thrust mode and the most advanced throttle control lever is in the CLB position.
THR: A/THR is engaged and active in thrust mode. The throttle control levers are neither in the CLB nor in the MCT position, or the A/THR is engaged and not active and the most advanced throttle control lever is between FLX TO/MCT and TO/GA position.
IDLE: A/THR is active in minimum thrust.
SPEED: A/THR is active in SPEED mode.
MACH: A/THR is active in MACH mode.
A. FLOOR: A/THR is active with the Alpha floor protection active.
TO/GA LK: A/THR is active with the Alpha floor protection active but the Alpha floor detection from the FAC is no longer present (TO/GA LK = TO/GA LOCK).

(b) On the FMA second line:

CLB: this amber message flashes to inform the crew to set the throttle control levers to the CLB position to permit normal A/THR in dual-engine configuration.
MCT: this amber message flashes to inform the crew to set the throttle control levers to the MCT position to permit normal A/THR in single-engine configuration.

ASYM: only one throttle control lever is in the MCT or CLB gate, resulting in asymmetrical thrust.

NOTE: The figures which show the display of AP/FD-A/THR messages according to the various typical flight cases are given in 22-10-00 AP/FD.

(4) Principle of messages displayed
All the messages are generated in the FMGCs and sent to the DMCs through discrete data, by the FCU on ARINC 429 bus.
The 3 DMCs acquire these discrete data to generate specific codes which correspond to the messages to be displayed on the PFDs.

(5) A/THR engagement status
The A/THR of message is displayed on the 3rd line of the right column in one of the two colors below.

(a) White
When the A/THR is engaged and active: the autothrust system controls the engines.

(b) Cyan
When the A/THR is engaged but not active: the two engines are controlled by the position of the throttle control levers and by the ECUs/EECs.

(6) A/THR modes
The A/THR modes are displayed on the left column if the A/THR is engaged.
Two different types of indications are displayed with appropriate colors.

(a) On the first line and second line, green and white messages indicate A/THR mode when:

the A/THR function is override by a throttle control lever set beyond the MCT position
the AP/FD active modes are: takeoff, landing go around, V/S or FPA, OPEN CLB, OPEN DES
the thrust is not consistent with the engine configuration (engine failure or not).

(b) On the third line, white flashing messages for action to be taken by the crew on the throttle control levers and amber messages for indication which requires special attention.

(7) Message meaning

(a) On the first line and second line:

MAN TOGA: A/THR is engaged, not active one throttle lever at least in TO/GA position, the thrust is under the control of the ECUs/EECs.
MAN FLX 50: A/THR is engaged not active . The takeoff is performed in FLX TO with a FLEX TO temperature (50 deg. C for example), selected on the MCDUs. One throttle control lever at least is in FLX TO/MCT position, the other one is in the same position or below.
MAN MCT: A/THR is engaged, not active. All throttles in MCT position.
THR MCT: A/THR is active in thrust mode and the most advanced throttle lever is in the MCT position (single-engine configuration).
THR CLB: A/THR is active in thrust mode and the most advanced throttle control lever is in the CLB position.
THR LVR: A/THR is active in thrust mode. The throttle control levers are neither in the CLB nor in the MCT position.
MAN THR: A/THR is engaged and not active and the most advanced throttle control lever is between FLX TO/MCT and TO/GA position or between CL and FLX TO/MCT.
THR IDLE: A/THR is active in minimum thrust.
SPEED: A/THR is active in SPEED mode.
MACH: A/THR is active in MACH mode.
A. FLOOR: A/THR is active with the Alpha Floor protection is active.
TOGA LK: A/THR is active with the Alpha Floor protection active but the Alpha Floor detection from the FAC is no longer present (TOGA LK = TOGA LOCK).

(b) On the FMA third line:

LVR CLB: this white message flashes to inform the crew to set the throttle levers to the CLB position to permit normal A/THR in dual-engine configuration.
LVR MCT: this white message flashes to inform the crew to set the throttle to the MCT position to permit normal A/THR in single-engine configuration.
LVR ASYM : only one throttle control lever is in the MCT or CLB gate, resulting in asymmetrical thrust.
The figures which show the display of AP/FD-A/THR messages according to the various typical flight cases are given in 22-10-00 AP/FD.

(8) Principle of messages displayed
All the messages are generated in the FMGCs and sent to the DMCs through discrete data, by the FCU on ARINC 429 bus.
The 3 DMCs acquire these discrete data to generate specific codes which correspond to the messages to be displayed on the PFDs.

[Rev.10 from 2021] 2026.03.31 23:10:07 UTC