1)  The VNAV mode engage logic is generated by three input conditions: F/D not disengaged, VNAV mode active, and VNAV engaged valid. The VNAV mode active means that the VNAV switch/light dot-bar matrix is lighted and the FMC is sending valid data.

 (b)
TAS Inverse Gain Schedule

 1)  The TAS inverse gain schedule control amplitude is inversely proportional to TAS and is used for gain schedule control.
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757
MAINTENANCE MANUAL

AUTOPILOT
LEFT, CENTER, CAPTAIN'S RIGHT COMMAND FIRST OFFICER'S FLIGHT DIRECTOR SPEED DISPLAY ENGAGE (CMD)FLIGHT DIRECTOR
(IAS/MACH)
ON/OFF SWITCH  SWITCH/LIGHT ON/OFF SWITCH

AIRSPEED/MACH  VERTICAL
SELECTOR SWITCH  NAVIGATION (VNAV) MODE SELECT SWITCH/LIGHT
4 5

. ALT SELECT DISPLAY MANUALY SET FOR ALT OF 30,000 FT (HIGHER THAN FMC ROUTE) 1 . ALT HOLD SW PUSHED AT 10,000 FT
-
V/S SWITCH DOT-BAR EXTINGUISHES

-
V/S DISPLAY BLANKS

-HOLD SWITCH DOT-BAR ILLUMINATES
-A/P LEVELS TO BARO-ALT AT TIME OF ALT HOLD
-FMA ON EADI IN PITCH MODE ENGAGES SECTION INDICATES ALT HOLD
2 . VNAV SW PUSHED
-HOLD SWITCH DOT-BAR EXTINGUISHES
-VNAV SWITCH DOT-BAR ILLUMINATES
-IAS/MACH DISPLAY BLANKS
-FMA ON ADI INDICATES VNAV
-AFDS UNDER FMC CONTROL 3 . FMC COMMANDS ELEVATORS FOR CLIMB
TO 25,000 FT AT PRESCRIBED RATE 4 . FMC COMMANDS ELEVATORS FOR LEVEL CRUISE 5 . FMC COMANDS ELEVATORS FOR DESCENT

Pitch Channel - Vertical Navigation (VNAV) Mode
Figure 14 (Sheet 1)

D01179
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757 MAINTENANCE MANUAL
SELECTED ALTITUDESPEED DISPLAY

VERTICAL NAVIGATION MODE SELECT SWTICH/LIGHT

. ALT SELECT DISPLAY MANUALLY SET FOR ALT OF 30,000 FT (HIGHER THAN FMC ROUTE) 1 . ALT HOLD SW PUSHED AT 10,000 FT
-
V/S SWITCH DOT-BAR EXTINGUISHES

-
V/S DISPLAY BLANKS

-HOLD SWITCH DOT-BAR ILLUMINATES
-A/P LEVELS TO BARO-ALT AT TIME OF ALT HOLD
-FMA ON EADI IN PITCH MODE ENGAGES SECTION INDICATES ALT HOLD
2 . VNAV SW PUSHED
-HOLD SWITCH DOT-BAR EXTINGUISHES
-VNAV SWITCH DOT-BAR ILLUMINATES
-IAS/MACH DISPLAY BLANKS
-FMA ON ADI INDICATES VNAV
-AFDS UNDER FMC CONTROL 3 . FMC COMMANDS ELEVATORS FOR CLIMB
TO 25,000 FT AT PRESCRIBED RATE 4 . FMC COMMANDS ELEVATORS FOR LEVEL CRUISE 5 . FMC COMMANDS ELEVATORS FOR DESCENT

Pitch Channel - Vertical Navigation (VNAV) Mode
Figure 14 (Sheet 2)

C71178
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MAINTENANCE MANUAL

 (c) Transition Control Logic From VNAV to ALT HOLD
 1)  The altitude hold auto engage logic is produced, for one iteration when it is enabled by VNAV mode engage and the following three conditions exist: a) The airplane is above or below the MCP selected
 altitude. b) The FMC is in the process of having the target altitude changed.
 c)  The FMC is notifying the AFDS that the next target altitude is farther away from the MCP selected altitude.
 (d) Transition Control Logic From VNAV to ALT SELECT
 1)  The altitude select auto engage logic is produced for one sampling when it is enabled by VNAV mode engage and the following four conditions exist: a) The airplane is above or below the MCP selected
 altitude. b) Altitude capture criteria are met. c) The FMC notifies the AFDS that the next target altitude
　
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