Bombardier Challenger AFCS Issues in Turbulence

[TA/RA]

I am just looking to see if there are any other CL601/604 drivers out there who are dealing with or have dealt with a sensitive AFCS.

We have experienced a few instances of the AFCS disabling itself in cruise when encountering turbulence. I understand that in Heavy turbulence the system is designed to kick off however we have experienced this phenomenon in both Moderate - Severe and Light-Moderate Chop.

Any feedback would be hugely appreciated.

Thanks much!

[wallypilot]

in 4 years on a 604, I haven't had this issue.

[xsbank]

Nope. Snag it.

You knew that an 'Autopilot disconnect' procedure is in the QRH in the Emergency section, didn't you?

[TA/RA]

You knew that an 'Autopilot disconnect' procedure is in the QRH in the Emergency section, didn't you?

Yes thank you, very well aware.

[Vickers vanguard]

First off, CL601 and CL604 AFCS are different, different hardware, different vendor. The cards that run the AFCS in the CL604/605 are supposed to remove any servo commands ( transparent to the user) when the craft experiences Pitch/roll rates that are above certain thresholds. However, it will not disconnect, unless even after the removal of those commands, the maximum pitch/roll attitudes or the max yaw rate have been exceeded...........it'll take a lot to do that, ex : max yaw rate @ 9 deg/sec.............max pitch up 25 deg..etc......
This is what I would do, try the other AFCS ( AFCS 2 if you're using AFCS 1 all the time), that will tell you if the snag relates to an FCC card or an external input. Second, does the yaw damper stays engaged after the A/P disengage ?

just like XSbank said, snag it. The problem would be finding qualified people to figure out the trouble. You need good factory trained avionic for that, unless you want to blindly replace all 4 FCC cards.

Finally, if you're referring to a CL601......guess what ? all the above does not apply.

[ChallengerDan]

And just to add to the above post, don't power the aircraft down once you get to your maintenance base if it has disconnected. The IAPS sends disconnects codes to the MDC FCC diagnostics page, which is the volatile type. Although some info does get transferred to the MDC memory, your trained avionic will most probably prefer the more complete FCC diagnostics as it will give him more information of the disconnect mode, servo status and values, etc.

1a/b and 2a/b can be swapped, too, before being replaced. That is what we usually do in the airline environment when we have no time and no parts. On the CRJ there is only 2 of them FCCs, not 4.

I've seen loose servo cables resulting in sensitive A/P too. FCC diagnostic will usually steer the tech in the right direction if he knows how to thread in there.