VOR/LOC 1. Roll engage
2.
VOR/LOC selected
3.
No VOR/ILS control panel test (if connected)
4.
No NAV transfer (if third navigation receiver installed)
NOTE: TURB selected when ILS frequency selected trips NAV mode switch to MAN. When on course, roll control wheel steering out of detent trips NAV mode switch to MAN.
HDG OFF 1. Roll engage
2. HDG OFF selected
AUTO APP 1. Roll engage
2.
Pitch engage
3.
AUTO APP or MAN G/S selected
542
22-11-0 Page 106 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 01/76
POSITIONCentered NAV
HDG SEL
PositionOFF ALT HOLD
TURB
4.
TURB not selected
5.
ILS frequency selected
6.
Air data computer altitude good
7.
No VOR/ILS control panel test (if connected)
8.
No NAV transfer (if third navigation receiver installed)
NOTE: When on course, roll control wheel steering out of detent, trips NAV mode switch to MAN. When glide slope is captured, pitch control wheel steering out of detent trips NAV mode select switch to MAN.
Mode Select Toggle Switch
Interlock
1. None (spring loaded to center)
1.
Roll engaged
2.
MAN selected
3.
NAV selected
1.
Roll engaged
2.
HDG SEL selected
3.
VOR or LOC not captured
4.
Roll control wheel steering not out of detent
Pitch Mode Select Switch
Interlock
1. Spring loaded to OFF from ALT HOLD
1.
Pitch engaged
2.
Air data computer altitude good
3.
Pitch control wheel steering not out of detent
4.
Glide slope not captured
1.
Pitch engaged
2.
TURB selected
Feb 01/76 22-11-0
Page 107
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(6)
The solenoid valves, transfer valves and position transducers on the hydraulic power packs have proven to be very reliable. A faulty solenoid valve circuit is indicated if the control wheel manually moves easily with the associated channel engaged. The control wheel/column is normally more difficult to move when the autopilot system is engaged due to the control wheel transducers providing signal output and the autopilot system in turn driving the control wheel. If the transducer valve or position transducer fail, the control wheel and associated control surface will also move to the extreme positions (Ref Hydraulic Power Pack Component Trouble Shooting Charts). Hydraulic power pack problems are usually indicated by operational faults when the autopilot system is not engaged such as sloppy centering of the control surfaces due to hydraulic wear or leaking seals (Ref Chapter 27, Flight Controls).
(7)
Faults involving the stabilizer trim circuits can usually be isolated between the pitch channel and the stabilizer trim servo circuits by use of the pitch channel self-test circuits. During airplane flight, the stabilizer trim circuits should cause the airplane to trim out any sustained output from the valve amplifier within approximately 12 seconds. If not, the stabilizer out of trim warning light illuminates; however, the pitch channel does not disengage. It should be noted that with the airplane on the ground and pitch channel engaged, operation of control wheel steering or any other signal input causes the stabilizer to trim to maximum up or down position unless the autopilot stabilizer trim circuit breaker is pulled. The stabilizer trim warning light also illuminates. It should also be noted that operation of the main electric stabilizer trim system causes the pitch channel to disengage (Ref Chapter 27, Horizontal Stabilizer Trim Control System). Stabilizer trim problems outside of the pitch channel must be traced down on a wire to wire basis until the fault is traced to a switch or stabilizer trim servo (Ref Stabilizer Trim Trouble Shooting Chart).
(8)
Trouble shooting the autopilot annunciator lights on the captain's or first officer's approach progress display is relatively easy since circuitry which controls the lights is primarily in the pitch and roll channels. A glide slope engage relay in the autopilot accessory box is controlled by the pitch channel vertical beam sensor circuits. Failure of both amber and green glide slope annunciator lights indicates lack of 28 volts dc from the autopilot control panel. Failure of only the green light indicates the vertical beam sensor, glide slope superflag circuits or the glide
slope relay is inoperative. The VOR/LOC annunciator lights are controlled by the lateral beam sensor and navigation receiver superflag circuits. Replacing the roll channel usually corrects VOR/LOC annunciator faults. The NAV annunciator is controlled by NAV selection and OMEGA valid logic to the autopilot control panel. Annunciators are also controlled by an automatic dimming circuit in the flight instrument accessory box and by photo cells on each pilot's instrument panel. Failure of all amber and green annunciator lights indicates a faulty dimming circuit in the flight instrument accessory box (Ref Autopilot Annunciator Lights Trouble Shooting Chart).
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