*
A/T mode
*
AFDS mode
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Parameters for A/T mode logic
*
MCP status.
The MCP sends this analog discrete data to the ASMs:
*
A/T arm (ON) switch supplies ASM control power in the on position
*
A/T arm (OFF) switch removes power (positive disengage) from its ASM in the off position.
ASM Digital Interface
The active TMCF causes the throttles to move forward or aft when it sends the ASMs digital commands. The ASM operation stops with the inhibit input. The A/T servo motors send digital throttle position (low speed tachometer) feedback data to the TMCFs when the servomotor moves. The autothrottle servo motors also send status information to the TMCFs.
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TMCS -A/T SERVO MOTOR
General
The integrated autothrottle servo motors (ASMs) are below the throttle quadrant (P10). The active TMCF sends servo rate commands to each ASM to move its throttle forward or aft through a separate gear box assembly.
Physical Description
The ASM weighs 1.9 pounds and measures 4.5 inches by 3.26 inches by 4 inches. The electrical power interface is from the bottom of the ASM.
Operation
Each ASM consists of these:
*
Electronic control module (ECM)
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Power supply unit (PSU)
*
Power switching module (PSM)
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Power switching bridge (PSB)
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DC motor with magnetic sensors.
Power to the ASM is 28v dc for excitation and motor control. The ASM pulse modulates and amplifies the digital servo rate commands it receives from the TMCF.
Each ASM receives analog (A/T arm and inhibit L/R) and digital (FMC selector position) discretes to enable its operation. Each ASM sends the TMCF a digital discrete of its state and digital rate feedback.
There are three magnetic pick-off sensors in the DC motor stator that measure rate feedback. These sensors measure the rate between the rotor and stator as the motor moves the throttle forward or aft.
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TMCS -A/T ARM, A/T MODE, AND THRUST LEVER SWITCHES
General
You use switches on the mode control panel (MCP) and on the thrust levers to arm, select, or disconnect A/T modes.
MCP A/T Arm Switch
The A/T arm switches are on the MCP. You use the A/T arm switches to enable ASM excitation power (28V dc) for operation. The on position (both) also supplies engine trim equalization control from the TMCFs. The off position removes power from that ASM and removes engine trim equalization control.
MCP A/T Mode Switches
The MCP has these A/T mode switches with these functions:
*
Climb/continuous (CLB/CON), selects the CLB thrust limit mode in the air or CON thrust limit mode in the air when one engine fails
*
A/T, selects the A/T speed (SPD) mode or the thrust reference (THR REF) mode when in the air
*
Flight level change (FLCH), gives a thrust command that changes with a small or large altitude change
*
Vertical navigation (VNAV), allows the throttles to operate with the autopilot flight director system (AFDS) to control thrust or speed.
To arm the autothrottle, move one or both of the A/T arm switches to the UP position. To engage the A/T, push the A/T switch on the MCP. The autothrottle engages automatically if any of these modes engage:
*
VNAV
*
FLCH
*
TO/GA.
Thrust Lever Switches
These switches are on the left and right thrust levers:
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Takeoff/go-around (TO/GA), S3, S5, and S7 (left) S2, S4, and S6 (right)
*
A/T disconnect.
Push a TO/GA lever to engage that TO/GA switch. This causes the selected takeoff (TO) thrust limit mode to operate on the ground. When radio altitude is more than 2 feet, a second push of a TO/GA lever removes any thrust derates. The thrust levers move to full takeoff thrust. On the ground, a second push of the TO/GA lever has no effect.
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