777 AIRCRAFT MAINTENANCE MANUAL
TMCS -A/T OPERATION -GO-AROUND
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TMCS -A/T OPERATION -FLARE RETARD
Mode Selection
The TMCF commands the throttles to move aft when all these conditions are true:
*
Flare retard command from the AFDS
*
Autothrottle arm switches on
*
Less than or equal to 25 feet radio altitude in a land configuration.
Operation
The TMCF sends a throttle rate command to the servo modules to cause the throttles to move aft. This action assists the AFDS flare maneuver in the final landing phase. The throttle retard action starts at 25 feet radio altitude. IDLE shows as the A/T mode on the PFD when flare retard starts.
The A/T disconnects when the flight crew applies reverse thrust. The landing phase inhibit logic prevents the display of the AUTHROTTLE DISC caution message on the EICAS display and does not let the caution aural operate.
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777 AIRCRAFT MAINTENANCE MANUAL
TMCS -A/T OPERATION -FLARE RETARD
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777 AIRCRAFT MAINTENANCE MANUAL
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TMCS -TMCF FUNCTIONAL DESCRIPTION -INTRODUCTION
General
The thrust management computing function (TMCF) controls engine thrust in response to commands from the guidance function of the flight management computing function (FMCF), the mode control panel, and flight deck switches.
The TMCF sub-functions are:
*
Thrust limit calculation
*
Engine trim equalization
*
Autothrottle (A/T)
*
BITE and fault monitoring
*
TMCF annunciations.
The TMCF uses digital and analog inputs from external sensors, digital and analog inputs from flight deck components, internal AIMS cabinet interface signals, and cross cabinet AIMS interface signals.
Thrust limit Calculation
The TMCF calculates maximum thrust and thrust limits for these thrust limit modes:
*
Takeoff (TO) thrust
*
Go-around (GA)
*
Climb (CLB)
*
Continuous (CON)
*
Cruise (CRZ)
*
Temperature derated TO
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* Fixed derated TO and CLB.
The TMCF uses these inputs to calculate thrust limits:
*
Temperature
*
Barometric altitude
*
Barometric pressure
*
Engine/airframe data bases
*
Thrust model data base
*
Flight deck inputs
*
Air/ground.
The thrust limits show on the EICAS display.
Engine Trim Equalization
The TMCF calculates engine trim commands to decrease the thrust difference between the engines. The trim function receives actual engine thrust data from each engine to do this. The incremental engine trim command goes to the EECs to change the engine thrust.
Autothrottle (A/T)
The A/T sub-function sets the thrust levers to capture and hold a thrust setting, or to hold a target airspeed.
To calculate the A/T function, the TMCF uses these:
*
Engage logic
*
Control Laws
*
Mode logic.
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TMCS -TMCF FUNCTIONAL DESCRIPTION -INTRODUCTION
The A/T uses inputs from these sources:
*
External sensor inputs
*
Flight deck switches and sensors inputs
*
Flight phase logic inputs
*
FMCF thrust, mode, and guidance request inputs
*
Internal and cross-cabinet AIMS inputs.
The engage logic determines the validity of the control law data and permits the software control laws to operate. The engage logic also sends logic that permits excitation voltage to the A/T servo motor (ASM). This permits the ASM to operate when it receives a command from the TMCF.
The control laws calculate the A/T command. It looks at the desired command and the actual airplane condition for that command. The error from these two is the error command.
The mode logic lets allows manual or automatic selection of the available autothrottle mode, thrust limit mode, and thrust limits. The A/T mode, thrust limit mode, and thrust limits show on the PFD and EICAS display.
BITE and Fault Monitoring
The TMCF BITE circuits do tests at power-up and throughout the TMCF operation. When the fault monitor circuits receives a test failure from the BITE, it writes the faults in the TMCF memory and sends the faults to the PDF (primary display function) and the central maintenance computing function (CMCF).
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