The A/THR sends to the FADEC the thrust targets that are needed to:
? Obtain and maintain a target speed, when in SPEED mode
? Obtain a specific thrust setting (e.g. CLB, IDLE), when in THRUST mode.
INTERFACE
When the A/THR is active, the thrust lever position determines the maximum thrust that the A/THR can command in SPEED or THRUST mode. Therefore, with A/THR active, thrust levers act as a thrust limiter or a thrust-rating panel.
The A/THR computer does not drive back the thrust levers. The PF sets them to a specific detent on the thrust lever range.
The A/THR system provides cues that indicate the energy of the aircraft:
? Speed, acceleration, or deceleration, obtained by the speed trend vector
? N1, and N1 command on the N1 gauge (or EPR, and EPR command on the EPR gauge).
All these cues are in the flight crew’s direct line of vision.
In other words, the Thrust Lever Angle (TLA) should not be used to monitor correct A/THR
operation. Neither should the thrust lever position of a conventional autothrottle, be considered a cue because, in many hazardous situations, the thrust lever position can be misleading (e.g. engine failure, thrust lever jammed).
The TLA Determines Max Thrust for the A/THR
NORMAL OPERATIONS
The A/THR can only be active, when the thrust levers are between IDLE and the CLB detent. When the thrust levers are beyond the CLB detent, thrust is controlled manually to the thrust lever Angle, and the A/THR is armed (A/THR appears in blue on the FMA). This means that the A/THR
is ready to be re-activated, when the flight crew sets the thrust levers back to the CLB detent (or below).
OPERATIONAL PHILOSOPHY
AP / FD / ATHR
A/THR operating sectors all engines operating
AT TAKEOFF
The thrust levers are set either full forward to TOGA, or to the FLX detent. Thrust is manually controlled to the TLA, and A/THR is armed. The FMA indicates this in blue.
AFTER TAKEOFF
When the aircraft reaches THR RED ALT, the flight crew sets the thrust levers back to the CLB detent. This activates A/THR. MAX CLB will, therefore, be the maximum normal thrust setting that will be commanded by the A/THR in CLB, CRZ, DES, or APPR, as required.
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