(4) Trouble shooting pitch or roll channel engage problems involves checking the interlock circuits for each channel to determine if the interlock voltages are available to the autopilot control panel. If interlock voltages are available, the autopilot control panel is probably faulty. However, engage circuits are also in the autopilot accessory box and pitch or roll channels. Therefore, replacement of the accessory box or a channel may be required. The engage circuit for the roll channel is also routed through a switch in the aileron force limiter. Faulty operation of the force limiter clutch may prevent engagement of the roll channel. Improper rigging or operation of the control wheel steering transducers may cause engagement difficulties even though they do not cause the pitch or roll channel to disengage once it is already engaged. It should be noted that transferring from VG-1 to AUX VG (if installed), or DG-1 to DG-2 causes the roll channel to disengage. Transferring from VG-1 to AUX VG (if installed) causes the pitch channel to disengage (Ref Chapter 34, Navigation). Airplanes which have glide slope and localizer superflag and glide slope relays in the interlock circuits will experience disengagement of the pitch and roll channels when on glide slope and a superflag is lost. This is normal. Airplanes without the glide slope and localizer superflag interlocks do not normally disengage the pitch and roll channels when a superflag is lost. (Refer to Pitch and Roll Channel Engage Trouble Shooting Charts.) To assist in trouble shooting, following is a list of the inputs required for pitch and roll channel engagement. Loss of any one of the inputs (except as noted) causes the channel to disengage.
Pitch Channel
1.
Elex bus-1 energized
2.
Battery bus energized (not on standby) (if interlock connected)
3.
Air data computer airspeed good
4.
30-volt dc monitor good
5.
Correct pitch calibrator installed
6.
Control wheel steering not out of detent (engage only)
7.
No trim monitor (engage only)
8.
No hot short - stab trim signal (disengage only)
9.
Flaps synchronized; no stabilizer trim speed change relay energized when flaps are up
10.
Autopilot stabilizer trim cutout switch in NORMAL
11.
Main electric stabilizer trim motor not operating
12.
Vertical gyro flag out of view
13.
Autopilot control panel good
14.
Autopilot accessory boxes good
15.
Flight control system B switch on
16.
Control wheel autopilot disengage switches not open
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Aug 01/74 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 22-11-0 Page 105
Roll Channel
1.
Elex bus-1 energized
2.
Battery bus energized (not on standby)
3.
Air data computer airspeed good
4.
30-volt dc monitor good
5.
Correct roll calibrator installed
6.
Control wheel steering not out of detent (engage only)
7.
Aileron force limiter clutch engaged - switch closed
8.
Vertical gyro flag out of view
9.
Directional gyro flag out of view (if interlock connected)
10.
VG and DG transfer relays good
11.
Autopilot control panel good
12.
Autopilot accessory boxes good
13.
Flight control system B switch on
14.
Control wheel autopilot disengage switches not open
(5) Selection of autopilot operational modes requires certain interlocks to be satisfied. During normal operation of the autopilot system, the navigation mode select switch, pitch mode select switch and heading mode select switch may be expected to return to MAN or OFF (heading switch to center) if certain interlocks fail. Failure reports involving abnormal operation of the switches require recognition of the interlocks required to keep the switch operative. Failure of any one of the interlocks may require replacement of the autopilot control panel, roll channel, pitch channel or autopilot accessory box (Ref Autopilot Mode Select Trouble Shooting Chart). Following is a list of interlocks required to keep each mode select switch coil energized:
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