22-11-01
 ú ú 02 Page 11 ú Feb 25/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 C.  The A/P (autopilot) ENGAGE switches are pushbutton type normally open, momentary contact switches which control an engage relay by means of electronic circuitry. Either channel is engaged to CWS (control wheel steering) or CMD (command) by pressing the appropriate switch. A light illuminates on the switch to indicate that the switch has been engaged, each switch may be disengaged by pressing the switch again. Loss of power (28v) or ground to the relay will cause it to de-energize and the pushbutton switch light will go out. If CWS or CMD is pressed while either power or ground for the relay is not provided, the relay will not energize and the pushbutton light will not illuminate. An additional means for disengaging the A/P is provided by the disengage bar. Pulling the disengage bar down will operate switches for both channel A and channel B. These switches disconnect the solenoid from the relay and connect it to a ground thus preventing the relay from energizing and the switches engaging. Operating the disengage bar will cause a light to illuminate behind the bar indicating it is in the disengaged position.
 D.  Two F/D (flight director) switches are provided for ON/OFF control of the A and B flight directors. Discrete signals are provided to the respective EADI and digital data is provided to the FCCs. A master light (MA) is located above each F/D switch to indicate which system (during slaved operation) is providing mode control.
 E.  The A/T (autothrottle) ARM/OFF switch is a two-position, solenoid-held switch for arming the autothrottle. On the ground, the FMCS must be engaged before the autothrottle can be armed. The ARM position permits A/T control of thrust levers when compatible mode selection exists between the A/P and A/T. The switch controls discrete circuits (Ref 22-31-00).
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 22-11-01
 ú ú 03 Page 12 ú Nov 15/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 F.  Flight mode selection is made with momentary pushbuttons. The flight modes are:
 V/S - Vertical Speed ALT HOLD - Altitude Hold V NAV - Flight Management Computer LVL CHG - Level Change - Airspeed Hold HDG SEL - Heading Select L NAV - Flight Management Computer VOR LOC - VHF NAV System (VOR, Localizer, Glideslope) APP - Approach SPEED - Autothrottle N1 - Autothrottle
 When CWS is selected on the MCP the A/P maneuvers the airplane in response to control wheel force applied by either pilot. When CMD is engaged the A/P maneuvers the airplane to fly according to the selected flight mode. If no flight mode is selected when in CMD the plane is maneuvered by CWS. Altitude aquire is automatically armed when no flight mode is selected. The mode switches are illuminated when the mode is ON, and pressing the switch again de-selects the mode. When on the selected altitude and in altitude hold, the ALT HOLD light is off indicating that ALT HOLD cannot be de-selected using the ALT HOLD pushbutton switch. A similar situation exists after LOC and G/S captured. The APP pushbutton light is off indicating that the APP pushbutton cannot be used to de-select the approach mode.
 G.  The IAS/MACH display and control consists of the speed display window, the rotary speed control knob and the pushbutton C/O (changeover), N1 (engine speed), SPEED, LVL CHG (level change), and VNAV (flight management computer) switches. These controls and displays are used for DFCS system control. The data is utilized in digital format and used by the A/T system (AMM 22-31-00), and the AP/FD systems. The switch legends use mode engaged digital data to operate the respective engaged (ON) legend. IAS/MACH selection is from 110 to 399 and 0.60 to 0.89 in movements of 1kt or 0.01M. IAS/MACH display is limited to the existing VMO/MMO. Additionally, the IAS/MACH LCD has flashing warning flags for underspeed and overspeed in the leftmost position. Underspeed (A) is displayed if the airplane speed is decreased to the minimum speed except in TO or GA. The A remains until the speed has been increased to 15 knots above the minimum speed. Overspeed is displayed when the airplane speed is greater than the VMO limit or speed is within 2 knots of the flap or gear placard.
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