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MAINTENANCE MANUAL

 3)  The dot-bar matrix lights on the mode select switch/lights are checked by the Master Dim and Test System (Ref (33-16-00).
 (c)
MCP Autopilot Mode Select Switch/lights

 1)  The mode select switch/lights provide mode request signals to both A and B channels of the MCP. The request also sets a bit in a digital word which is transmitted to the FCC or TMC. The illumination of the dot-bar matrices of these switches is controlled by mode status logic generated in the engaged FCC(s) or TMC. No illumination is provided for the IAS/MACH SEL switch or the HDG SEL switch.

 (d)
MCP Autopilot Reference Data Controls and Displays

 1)  Reference values for altitude, heading, vertical speed, and airspeed or mach number are entered using the related select knob or thumbwheel on the MCP. These reference values are optically encoded and supplied to both the A and B channels and routed to the appropriate MCP window for display. The reference values are also sent to the FCC, FMC, and TMC.
 (e) Vertical Speed Mode 1) When the vertical speed (V/S) mode select switch/light is pressed, a V/S mode request discrete is initiated. This discrete generates a manual ON signal which arms the vertical speed mode if the FCC is engaged in CMD or the F/D is on and the airplane is airborne. The vertical speed mode is automatically initiated by an engaged FCC (CMD or F/D) if no other pitch modes are selected or engaged (Ref 22-12-00).
 2)  The dot-bar matrix annunciator in the V/S switch/light illuminates when the MCP receives V/S OPER from the FCC's. V/S OPER is also sent to the EFIS symbol generators for mode display on the EADIs. Once V/S mode is engaged, it can be disabled if CMD is disabled and both the F/Ds are turned off. The V/S mode will also be disabled by the selection of the following pitch modes: ALT HLD select, FLCH select, VNAV select, APP select, or GA select.
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757
MAINTENANCE MANUAL

 3)  The V/S pushbutton can also be illuminated using the TEST switch on the master dim and test panel. This test input checks MCP circuits (data management) as well as the dot-bar matrices.
 (f) Heading Hold Mode 1) Pressing the HDG HOLD mode select switch/light initiates a heading hold mode request discrete. This discrete generates a manual ON signal which arms the heading hold mode if the FCC is engaged in CMD or the F/D is on and the airplane is airborne. The heading hold mode is automatically initiated by an engaged FCC (CMD or F/D) if no other roll modes are selected or engaged (Ref 22-13-00).
 2)  The dot-bar matrix annunciator in the HDG HOLD switch/light lights when the MCP receives HDG HOLD OPER from the FCC's. HDG HDL OPER is also sent to the EFIS symbol generators for mode display on the EADIs. Once HDG HOLD mode is engaged, it can be disabled if CMD is disabled and both the F/Ds are turned off. Heading hold is also disabled by selection of the following modes: HDG select, LNAV select, LOC override, or GA select.
 (g) Altitude Hold Mode 1) Pressing the ALT HOLD mode select switch/light initiates an altitude hold mode request discrete. This discrete generates a manual ON signal which arms the altitude hold mode if the FCC is engaged in CMD or the F/D is on and the airplane is airborne. Altitude hold can also be automatically initiated by an engaged FCC (CMD or F/D) during altitude capture (Ref 22-12-00).
 2)  The dot-bar matrix in the ALT HOLD switch/light lights when the MCP receives ALTITUDE MODE OPER from the FCC(s). ALT HLD OPER is also sent to the EFIS symbol generators for mode display on the EADIs. Once altitude hold mode is engaged, it can be disabled if CMD is disabled and both the F/Ds are turned off. Altitude hold will also be disabled by selection of the following modes V/S select, FLCH select, VNAV select, APP select, or GA select.
 (h) Thrust Mode 1) Pressing the EPR mode select switch/light initiates a thrust mode request discrete. This discrete results in a thrust mode select signal if the autothrottle (A/T) is armed and operating with no faults while the airplane is either on the ground, in the air, or in the takeoff mode.
 2)  The dot-bar matrix in the thrust mode select switch/light lights when the MCP receives THRUST MODE OPER from the TMC. Once the thrust mode is engaged, it can be disabled if the A/T is disengaged or another mode is selected (SPD select, FLCH select, or VNAV select).
　
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