7.  Approach Progress Display Operation
A.  The approach progress display provides annunciator light (VOR/LOC and GLIDE SLOPE) indication when a radio mode is selected (VBS or LBS armed) on the autopilot control panel and when the vertical or lateral beam sensors have operated to capture a VOR radial, LOC beam or glide slope beam. The NAV mode is annunciated whenever the OMEGA system is operational and NAV is selected on the autopilot control panel. The annunciators also display HDG SEL or ALT HOLD when either of these modes have been selected. The displays on each pilot's instrument panel are paralleled together to the control panel and pitch and roll channel logic circuits. Five annunciator lights are used on the display; amber for VOR/LOC or (GS) armed and green for VOR/LOC, GS, HDG SEL, ALT HOLD or NAV captured. Other annunciator lights on the display are spares or are associated with the flight director system (Ref Chapter 34, Flight Director System).
B.  The approach progress display lights can be tested by pressing the display; power from the autopilot warning lights circuit breaker is then completed through all lights, thereby indicating if all lights are operable (Fig. 20). The ground side of the annunciator lights is connected to a dimming module in the flight instrument accessory box. A photocell on each pilot's instrument panel senses background light conditions and, through the dimming circuit, keeps the annunciator lights at the same relative brightness. The master dimming switch on the center instrument panel also controls the annunciator lights. When the switch is positioned to BRT, the dimming circuit is bypassed and the annunciator lights remain at maximum intensity.
C.  The VOR/LOC annunciator is controlled by logic in the roll channel. The VOR/LOC light illuminates amber whenever the mode selector switch is in any position except MAN or HDG OFF. If the VOR/LOC super flag logic is available, the VOR/LOC annunciator light turns green whenever the LBS drops out (VOR/LOC capture). The GS annunciator is controlled by the pitch channel. Selection of AUTO APP completes 28 volts dc to illuminate the glide slope annunciator amber. Power for the glide slope annunciator lights is completed through the glide slope relay in the autopilot accessory box. If the glide slope super flag logic is available, the glide slope relay is energized and the glide slope annunciator turns green whenever the VBS drops out (glide slope capture). Once the annunciator has turned green, loss of LBS/VBS or superflag logic does not return the light to amber or off. MAN or HDG OFF must be selected to extinguish the light. The ALT HOLD annunciator light is controlled by logic in the pitch channel as shown in Fig. 20. The NAV and HDG SEL annunciator lights are controlled by switching and logic in the control panel.
8.  Autopilot Mode Select Operation
A.  General
(1)  The various autopilot modes are selected on the autopilot control panel. Some modes require only the pitch or roll channels to be
5C4 
Jan 20/83  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  22-11-0 Page 67 

Autopilot Approach Progress Display Circuit (Simplified)  5C4 
22-11-0  Figure 20  Jun 20/85 
Page 68 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

engaged, others require both channels to be engaged (Fig. 21). The logic required to keep a selected mode engaged has been previously covered. The following discussion covers typical uses of the different switches and when they can be used in relation to each other. It is assumed all logic inputs are available for switch engagement. Figure 21 provides a summation of the different switch positions, where the primary signals originate and the associated roll rates and bank limits. The charts may be useful when studying the roll and pitch channel block diagrams and the operation of the autopilot system.
B.  Mode Select Switch
(1)  
The basic autopilot mode is MAN. The mode select switch must be in MAN to engage either the pitch or the roll channels. The airplane may be banked or pitched at any angle, but as long as control wheel steering is in detent, the pitch and/or roll channels can be engaged. The heading-nav mode select switch must be centered and the pitch mode select switch off. The pitch channel maintains the airplane at the same attitude existing at the time ELEV switch is engaged. The roll channel maintains the airplane at the same attitude existing at the time the AIL switch is engaged if the bank angle is greater than 5 degrees. If the bank angle is less than 5 degrees, the wings roll level and, after 1 to 2 seconds, the airplane flies on established heading. If the roll channel is engaged at a bank angle greater than 32 degrees, the airplane rolls upright to a 32 degree bank angle and then maintains the established attitude (attitude hold). Low detent is used by control wheel steering when MAN is selected, provided the pitch mode select switch is not in ALT HOLD and the heading-nav mode switch is not in HDG SEL or NAV. Control wheel steering enables the pilot to manually control the airplane through the autopilot pitch and roll channels. The control wheel is moved and the airplane flown just as it would be without the autopilot system engaged. The airplane will remain at the attitude or bank angle as established by the pilot (and modified by the mode limitations) whenever the control wheel or column is returned to center (in detent). The detent levels are established to ensure positive control inputs by the pilot and to ensure against any accidental control inputs which may occur.
　
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