(3)  There are two heading and two course synchro-resolvers which provide error signal to the flight director computers proportional to the difference between the actual and selected course or heading. The error signals are developed in relationship to magnetic heading signals as fed from the RMI's. The heading and course synchro resolvers which feed the error signals to the captains system also feed these same signals to the autopilot system.
5.  Flight Director (Steering) Computer
A.  The flight director computer for each flight director system provides the bank and pitch steering commands, which are displayed by the V-bars in the ADI. The V-bars then provide the pilot with a visual indication of the action he must take to maintain the airplane at a specified pitch attitude and heading. The computer also provides a computer flag signal to the ADI that allows the flag to come into view indicating that the steering commands are unreliable. The computer also provides signals to operate the Flight Director annunciators that indicate the type of navigation data being used to compute the steering commands.
B.  Information concerning radio deviation, selected heading and bank angle are used in the computation of the bank steering command signals, and information concerning pitch attitude, glide slope deviation, or altitude information are used in the computation of the pitch steering command signals. From this division of the input signals, two signal flow channels result in the computer: bank and pitch. The functioning of these channels is described later under Operation and is shown in Fig. 3.
C.  The computer also contains two power supply circuits, termed attitude and heading power. The inputs however are connected together, and power to the computer is from a single source. The computer also contains a warning flag circuit plus several logic circuits. The logic circuits are used in switching of the computer to the various modes of operation. Some of these logic circuits are controlled from the flight director control panel, and others are controlled internally in the computer. The CMPTR warning flag is actuated by a warning flag signal fed from the warning flag circuit. This circuit in addition to monitoring all of the various input warning signals, also monitors the V-bars and power to the computer.
6.  Approach Progress Display
A.  The flight director (F/D) approach progress display (ADP) annunciators are located on the flight instrument panels (Fig. 1). The annunciators provide a bi-color (amber and green) indication of the type of navigation data being used to compute the steering information displayed by the ADI V-pointers.
B.  The VOR/LOC and GS annunciators will illuminate amber (arm) when the flight director operating mode is selected and at the instant of beam capture, the annunciation will change to green (engage). The GO-AROUND (GA) light will light green when the GA mode is selected. The ALT HOLD light will come on green when the altitude hold mode is selected. The HDG SEL light will come on when the HDG mode has been selected and in the HDG V/L and AUTO APP mode when selected from the HDG position.
C.  Push-to-test circuitry is provided to check light operation. The voltage level, and consequent light intensity, is automatically changed by a photocell for day and night operation. The intensity of the annunciator lights may be manually reduced by placing the LIGHTS switch on the center instrument panel to DIM.
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34-26-0 Page 12  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 20/85 

7.  Air Data Computer
A.  The air data computer is a device for detecting changes in static pressure altitude, as supplied from the airplane static system. Once altitude hold is selected, any deviation in pressure altitude will result in an error voltage being supplied to the computer pitch channel. The pitch command output positions the V-bars to visually show the airplane attitude necessary for a smooth return to the desired pressure altitude. The air data computer is described in 34-12-0, Central Air Data System.
8.  Operation (Fig. 3)
A.  Before the flight director systems can be operated, the vertical gyro, air data system, compass, and VOR/ILS navigation circuit breakers must be closed and the systems must be operational. Closing the circuit breakers shown in Fig. 3 provides power to the flight director system.
B.  When the mode selector is in the OFF or the NAV (INOP) position, the command bars and the CMPTR warning flag in the ADI will move out of sight when power is applied to the system. In this mode, as well as in all other modes, the CMPTR warning flag monitors power to the computer. Turning the mode selector switch to any one of the other modes causes the V-bars to come into sight.
C.  In the roll channel, the bank error signal (which is developed in the attitude reference system when the airplane is banked) is compared against the computed bank command signal to yield the bank steering command signal. Similarly, in the pitch channel, the pitch error signal, or altitude error signal is compared against the computed pitch command signal to yield the pitch steering command signal. The inputs that alter gain and control switching of the circuits in the various modes are shown on Fig. 3. Switches are shown, but in the computer, transistors handle the switching.
　
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