*
MCP A/T mode request

*
Air/ground

*
Flaps not up or glideslope capture

*
Ambient conditions (ALT, TEMP and pressure).

The CDU supplies both the thrust limit mode requests and the fixed and temperature derate selections on the THRUST LIMIT page. The fixed derate applies to the TO and CLB thrust limit modes. Temperature derate applies to the TO thrust limit mode only.
The MCP A/T mode request (A/T or FLCH) causes the thrust limit process to calculate and show the CLB thrust limit. This shows on the EICAS display as a digital readout and a green thrust cursor.
For a VNAV A/T mode request on the MCP, the thrust limit process recalculates the thrust limit mode for FMCF comparison. When VNAV engages, FMCF supplies the thrust limit modes and thrust limits to the EICAS display in the climb, cruise, and descent flight phases. The thrust limit process calculates the GA thrust limit when the flaps are not up, at glideslope capture or GA A/T engagement.
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TMCS -TMCF FUNCTIONAL DESCRIPTION -THRUST LIMIT CALCULATION

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TMCS -TMCF FUNCTIONAL DESCRIPTION -ENGAGE LOGIC

General
The A/T engage logic process monitors the TMCF parameters for A/T mode engage. The TMCF sends an analog enable discrete to the A/T servo motors (ASM) when conditions are valid. The logic also generates ASM commands and an autothrottle disconnect signal.
Servo Loop Monitor
When the A/T engages, the control law sends rate commands to the ASMs. The ASMs send rate feedback (tachometer data) to the TMCFs. The servo loop monitor compares these two signals and sets the inhibit logic when they do not agree. This causes the ASMs to disconnect. BITE (TMCF and ASM) failures also set the inhibit.
Autothrottle Disconnect
When the A/T disconnects automatically or manually, the AUTOTHROTTLE DISC caution message shows on the engine primary format display. BITE sets the A/T disconnect. Push an A/T disconnect switch to cause a manual A/T disconnect.
The A/T also disconnects on the ground when the flight crew applies reverse thrust. For this, there is no A/T disconnect message or caution aural.
The AUTOTHROTTLE DISC is a caution message that causes the master caution lights to come on and an aural four beep alert to sound in the flight deck.
Inhibit L/R
The active TMCF causes the ASMs to disconnect when it sets the left and right inhibit switches.
TMCF Selection
The TMCF selection is similar to the FMCF selection. Use the FMC selector to make the left or right TMCF active.
The FMC selector is a three position switch; L (left), AUTO, and R (right). In the L position, the left TMCF and FMCF are active. If the left TMCF fails, there is no active TMCF. In the AUTO position, a random selection of the active TMCF and FMCF occurs after power is supplied. If the active TMCF fails, the other TMCF becomes active. In the R position, the right TMCF and FMCF are active. If the right TMCF fails, there is no active TMCF.
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TMCS -TMCF FUNCTIONAL DESCRIPTION -ENGAGE LOGIC

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TMCS -FUNCTIONAL DESCRIPTION -A/T SERVO MOTOR

General
These are the functions of the autothrottle servo motor (ASM):
*
ARINC 429 rate command decoding

*
Tachometer and power feedback decoding

*
Enable/disable logic

*
Inner loop servo motor rate control.

The ASM has these components:
*
Power supply unit (PSU)

*
Power switching module (PSM)

*
Electronic control module (ECM)

*
DC motor.

Power Supply Unit
The PSU provides internal power for the ECM and the PSM.
Power Switching Module
The PSM has a series of enable switches that send an output to a power switching bridge. These switch inputs are based on these inputs to the input controller:
*
Left and right arm from the MCP

*
Left TMCF and right TMCF inhibit

*
Left, right or auto from the FMC selector.

The output to the power switching bridge lets the bridge process the drive signals.
The enable switches also send an output to the ECM.
Electronic Control Module
The ECM contains the circuitry to calculate the drive commands for the DC motor. The ECM gets inputs through the ARINC 429 receivers and the input controller. It also gets feedback signals from the rate sensors of the DC motor.
　
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