777 AIRCRAFT MAINTENANCE MANUAL
AFDS -ILS ANALOG DISCRETES INTERFACE
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AFDS -BACKDRIVE INTERFACE
AFDC Backdrive
The left and right autopilot flight director computers (AFDCs) each connect to three backdrive actuators. These are the actuators:
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Column backdrive actuator
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Wheel backdrive actuator
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Rudder backdrive actuator.
Each actuator has these components:
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Two tachometers
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One motor
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One clutch.
The AFDCs send the control signals to the motor and clutch and receive actuator rate from the tachometers.
The center AFDC does not connect to any backdrive actuators.
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777 AIRCRAFT MAINTENANCE MANUAL
AFDS -BACKDRIVE INTERFACE
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AFDS -MODE CONTROL PANEL -PHYSICAL DESCRIPTION
Purpose
The mode control panel (MCP) supplies the interface between the pilot and the autopilot flight director system (AFDS).
The displays on the MCP show the selected values of airplane speed, heading, and altitude.
The MCP lets the flight crew engage and operate the AFDS and the AIMS thrust management computer function (TMCF).
Physical Description
The MCP weighs approximately 16 lb. Four screws hold the MCP to the glareshield structure. They connect to floating locknuts in the bottom of the MCP. The screws are captive in the mounting rails.
Three quick-disconnect connectors on the rear of the MCP supply 28v dc power and 5v ac panel lighting. They also connect ARINC data buses and discrete inputs and outputs.
Forced air from the equipment cooling system goes in the rear of the MCP and goes out through exhaust holes at the top. The MCP automatically connects with the cooling system when you install the MCP.
Each switch assembly has two incandescent bulbs. The bulbs are in the back of the switch assembly. The bulbs use 5v ac power from the master dim and test circuits. To replace the incandescent bulbs, remove the switch assembly from the MCP.
Each mode select switch, except the CLB/CON switch, also has a 28v dc light emitting diode (LED). The LEDs show a bar at the bottom of the switch. The LEDs are not line replaceable.
There are four liquid crystal displays (LCD) to show these reference values:
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Indicated airspeed (IAS) or MACH
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Heading (HDG) or track (TRK)
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Vertical speed (V/S) or flight path angle (FPA)
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Altitude.
The LCDs are not line replaceable.
The light source for the four LCDs is a fluorescent tube. The tube is inside the MCP and is behind the LCDs. The tube is not line replaceable.
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AFDS -MODE CONTROL PANEL -PHYSICAL DESCRIPTION
Training Information Point
As the fluorescent tube gets old, the current to the tube increases to maintain the brightness. A current monitor detects the current to the tube. If the current reaches a threshold limit, the MCP sends a request to the CMCF to make a maintenance memo. The maintenance memo is mode control panel fluorescent light is degraded. You select the maintenance memos with the maintenance planning menu on the MAT.
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AFDS -MODE CONTROL PANEL -PHYSICAL DESCRIPTION
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AFDS -MODE CONTROL PANEL -FUNCTIONAL DESCRIPTION
General
The major components of the MCP are:
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Power supplies, A and B
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Microprocessors, A and B
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Fluorescent tube control
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LCDs and encoders
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Push-button and toggle switches.
Power Supplies A and B
Power supplies A and B receive 28v dc from the left and right 28v dc buses. The MCP functions with either source of 28v dc.
Power supplies A and B supply +12v dc, -12v dc and +5v dc to their microprocessors and logic circuits. Power supplies A and B also supply +14v dc to power supply C which is part of the fluorescent tube control.
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