 |
|
ATA 22 Autoflight
1 - When the autopilot disconnects after 3.5 seconds... 737-300/-400/-500
2 - Yaw damper disengages with Fault code 22-21006 737-6/7/8/900
3 - Yoke kicks when Autopilot engages. 737-ALL
|
|
1 - When
the autopilot disconnects after 3.5 seconds....
737-3/4/500
Then probably one of the 4 autopilot actuators (2 aileron and 2 elevator) pressure switches is faulty.
This pressure switch senses hydr. pressure after the actuator is engaged by the autopilot. (feedback signal)
However, the time from engaging the a/p and actuation of the pressure switch takes approx 3.5 seconds.
And when this switch fails, what happened in the past, then the a/p disconnects again.
So before replacing any black boxes or doing extensive a/p tests, first check this switch which you can find on each a/p actuator.
2 -
Yaw damper disengages
with Fault code 22-21006 737-6/7/8/900
Discrepancy: Yaw damper disengages with Fault code 22-21006
Possible Fix: Rudder PCU or wiring
Tip: If during Yaw damper system test, the Sweep tests fails. Test the Servo
loop system, this is the solenoid, the transfer valve and LVDT feedback. If that
test is good you can go to the Rudder PCU and verify by watching the PCU that it
engages and attempts to move during the sweep test if not. Verify the solenoid
engage ciccuit, (D291 pin 1 and 2).
Reason/Explanation: During the Sweep test the #1 SMYD will send a electrical
command to the transfer valve to displace the PCU then look for a feedback of
LVDT position in the amount that is expected in movement. The FIMM procedure
instructs you to "check the wiring after you have replaced the PCU, if the
problem persists". Since you will be at the PCU when you go to replace it you
might want to verify solenoid engagment and movement before you take the time to
change it.
Applicable Reference: FIMM 22-23-task 809, AMM 22-23-00-710-802, WDM 22-23-12
Thanks to Tom S. for his input !
3 -
Yoke kicks when Autopilot engages.
737-ALL
Discrepancy: Yoke kicks when Autopilot engages
Possible Fix: Adjust the autopilot actuator input rod to the affected flight
control surface.
Tip: Adjust both Autopilot system actuator rods for that control surface even if
only one is kicking. Adjusting one rod may effect the adjustment of the other.
Reason/Explanation: It is in the MM to adjust the rod when you replace the
actuator. If this adjustment if off, after the actuator sync's the second
soleniod engages it to the surface, and will kick if it is off.
Applicable Reference: AMM 22-11-25-820-801
Thanks to Tom S. for his input !
|
|