Copyright D.P. Browne 2011
The Auto thrust system is part of the FMGS and controls the engine thrust via the FADEC in order to maintain the target values of Speed,Mach, or Thrust. The A/THR is active when the A/THR is indicated in white on the FMA and the A/THR button is green on the FCU.
Auto Thrust Modes
The speed/mach mode adjust the engines thrust to maintain a target speed. The target speed may be the FCU speed (selected) or a managed speed from the MCDU.
This mode commands a specific thrust settings from the engines. The thrust setting is dependant upon the thrust lever setting.
The Retard mode is activated automatically during an automatic landing ( A/P engaged in LAND/FLARE mode). The Retard mode is activated at 40 feet radio altitude.
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THR MCT |
Single engine Max continuous thrust |
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THR CLB |
Climb thrust two engines |
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THR LVR |
Undermined thrust |
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THR IDLE |
Minimum thrust |
The A/THR will acquire an hold the target speed within the following limits.
Green Dot
S,F limit speeds
Selected Speed Target
Managed Speed Target
VFE
VLE
VMO
VVO
S,F limit spee ds
VLS
The Retard mode reduces the engine thrust to idle, during the landing flare. The FMA shows “IDLE”. If the A/P is disconnected during the flare and before touchdown, then Retard mode will change to the Speed mode. The flight crew must manually reduce the thrust in this case.
The Thrust mode engages automatically if the A/P mode engages in one of the climb or descent modes.
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AP F/D mode |
A/T mode |
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V/S or FPA ALT * , ALT, ALT CRZ, ALT CST G/S * , G/S FINAL, FINAL APP DES (Off path)
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SPEED / MACH |
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CLB/OP CLB DES ( On path) , OP DES EXP CLB , EXP DES SRS |
THRUST / IDLE |
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FLARE, |
RETARD |