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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.
D.  HDG Mode
(1)  
In the HDG mode of operation, the steering computer provides computed roll and pitch steering commands to the ADI for the pilot to follow in order to capture or maintain a selected heading and hold a selected pitch angle or altitude. The computer will develop steering commands, up to a roll limit of 30 degrees and a pitch limit of 12 degrees, which are displayed on the V-bars. Switching the mode selector to HDG causes the computer to operate in the heading mode.

(2)  
In the roll channel, the computer uses heading error signals and bank attitude signals to compute lateral steering commands. The heading error signal is supplied from the heading error control transformer in the flight director control panel and is proportional to the difference between the pilot's selected heading and the magnetic heading. The bank attitude signal is generated by the vertical gyro. In the computer, the HDG signal generated by the mode logic enables the heading error signal to pass thru the switch to the summing networks and then the bank limiter. After being limited, the error signal is summed with the bank attitude signal. The summed (difference) signal is the difference between the heading error and commanded bank (attitude) signals. The summed signal is amplified and converted to a dc signal to become the bank steering command output from the computer to the ADI.

(3)  
In the pitch channel, the computer uses the pitch attitude signal and either a manual pitch or altitude error signal to compute vertical steering commands. The pitch attitude signal is supplied by the attitude reference system and is proportional to the airplane pitch angle. The manual pitch commands are supplied from the flight director control panel as selected on the pitch command knob. The air data system supplies altitude error signals during the altitude hold submode.

(4)  
In the manual pitch submode; the manual pitch signals are proportional to the desired pitch attitude from horizontal as set on the pitch command knob. In the pitch channel, the pitch attitude signal is summed with the manual pitch command signal. The resultant is the difference between the actual attitude and commanded pitch. This signal is amplified and converted to a dc signal to become the pitch steering command to the ADI.

(5)  
The altitude hold submode is enabled by placing the altitude hold switch on the flight director control panel to on. In the mode logic, this generates the ALT HOLD logic signal and turns the MAN PITCH logic signal off. At the summation point, the altitude error signal is summed with the pitch attitude signal from the low-pass filter (15 SEC delay network). The resultant signal is the pitch command signal that is required to maintain the desired altitude. The resultant signal is amplified and limited. It is then combined again with the pitch attitude signal. This produces a signal proportional to the difference between the commanded pitch and actual pitch. This signal is amplified and converted to a dc signal to become the pitch steering command to the ADI.

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Feb 15/79  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-26-0 Page 13 

E.  VOR/LOC Mode
(1)  
In the VOR/LOC mode, the bank steering command signal provides steering command information to intercept and hold the selected VOR, or LOC course. The VOR/LOC position on the mode selector causes the computer pitch channel to operate in the manual pitch or altitude hold modes and the bank channel in either the VOR or LOC modes. When the navigation receiver is tuned to a localizer frequency, an ILS 28-volt dc signal is provided to the mode logic for selecting the localizer mode. In the absence of this signal, the computer will operate in the VOR mode. For VOR operation, the steering commands are limited to 25 degrees in roll and for LOC operation, the steering commands are limited to 30 degrees prior to and 15 degrees after the APPR signal has been generated. Pitch steering commands are limited to 12 degrees. The action is similar for either course, except that in LOC tighter coupling is provided. This is accomplished through logic circuits that alter the various gains and limits of the associated circuits.
　
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