TMCS -TMCF FUNCTIONAL DESCRIPTION -AUTOTHROTTLE CONTROL LAWS
The TMCF calculates the trim equalization command as the difference between the trim reference and each engine EPR. If both EECs are in the alternate mode, the trim equalization command is the difference between the trim reference and each engine N1.
The trim equalization command from the TMCF to the EECs goes to zero when one of the engines EPR is more than 0.08 EPR below the engine with the higher EPR (0.16 EPR for altitudes above 20,000 feet).
The trim equalization command goes to zero if you move one throttle lever away from the other.
For autothrottle operation on the ground and in the air, trim equalization operates at A/T engagement and when these conditions are available:
*
Both A/T arm switches are on
*
The EECs show that the engines are not failed
*
Both engines are in the same mode (normal/alternate)
*
Valid data is present.
Thrust Limit Protection
Thrust limit protection provides airframe and engine envelope protection (engine exceedance) in the operating environment. Thrust limit protection shows as thrust limit on the EICAS display and as a speed limit on the primary flight display (PFD). In the TO mode and other A/T modes, the thrust limit protection process gives this protection:
*
Maximum speed
*
Placard speed
*
Configuration speed.
This protection occurs when the airplane is above 400 feet AGL. Autothrottle wake-up mode is another name for this protection.
In the GA mode, maximum and flap placard speed protection occurs when the thrust control law commands the full GA thrust limit.
Pilot Override Logic
A pilot override occurs when a pilot moves the throttles manually to a position that differs from the ASM command by eight degrees. If the pilot does this when the autothrottle mode is FLCH (THR shows on the PFD), the A/T mode on the PFD changes to HOLD. The TMCF removes excitation power from the ASMs. The pilot must change to another autothrottle mode to reset the FLCH mode.
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TMCS -TMCF FUNCTIONAL DESCRIPTION -AUTOTHROTTLE CONTROL LAWS
The throttles return to the A/T commanded position when a pilot override stops and the autothrottle is in any of these modes:
*
Speed (SPD shows on the PFD)
*
VNAV (SPD shows on the PFD)
*
Takeoff (TO) thrust
*
Go-around.
A/T Servo Motor Control
Each control law (SPD, V/S, and THR) sends an error command for the A/T mode it calculates. The servo control integrates the error command and sends it to each A/T servo module.
The ASMs move the throttles in rate control. The ASMs move the throttles at eight degree per second forward or aft. Rate feedback increases until it agrees with the throttle rate command. This results in a constant output from the ASMs and the throttles move at a constant rate of eight degree per second.
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TMCS -TMCF FUNCTIONAL DESCRIPTION -AUTOTHROTTLE CONTROL LAWS
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TMCS -TMCF FUNCTIONAL DESCRIPTION -THRUST LIMIT CALCULATION
General
The thrust limit calculation part of TMCF has the thrust rating mode logic, limit calculation equations and the associated logic and data base.
The TMCF thrust limit calculations are:
*
Maximum thrust
*
Thrust limits for A/T thrust limit modes.
Maximum Thrust
The maximum thrust calculation uses these inputs:
*
Baro altitude from the ADIRU
*
Temperature from the ADIRU
*
Baro pressure from the ADIRU
*
Gross weight from the FMCF
*
Engine/airframe data from the performance data base (PDB).
This is the maximum thrust the engine can deliver. Maximum thrust shows on the main EICAS display thrust indicators. A thrust derate (fixed and/or temperature) can not decrease this calculation. However, a derate can decrease the takeoff (TO) thrust limit calculation of the day.
All the thrust limit modes show on the CDU and the EICAS display.
Thrust Limits
The thrust limit calculation for A/T modes uses these inputs:
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