KFC 150 A/P issue

[VA FLYER]

My autopilot has good days and bad days. Last week, it flew perfectly for 1.5 hours. This week, it ran fine for 5 minutes and then started  uncommanded rolls 30 degrees left and right. Restarting had no effect, except it no longer worked for the 5 minutes. Alt hold seems to work but I never let the runaway get far enough to really tell. Same result on NAV or HDG mode. This has happened before, but I’ve installed a new HSI (G275) since the last occurrence. Now, the gremlins are back! Ideas? 

[Jake@BevanAviation]

If the aircraft is banking more than the standard rate turns (approximately 20-22deg bank), that sounds more like a AI issue.  When this happens if you tell it to turn right 90 deg it will continue to turn right until you tell it to stop, they are overly aggressive in commands due to the missing information from the AI to limit the response of the autopilot.  If you don't tell the system to stop turning, they will turn over on itself.

[Fly Boomer]

6 minutes ago, Jake@BevanAviation said:

If the aircraft is banking more than the standard rate turns (approximately 20-22deg bank), that sounds more like a AI issue.  When this happens if you tell it to turn right 90 deg it will continue to turn right until you tell it to stop, they are overly aggressive in commands due to the missing information from the AI to limit the response of the autopilot.  If you don't tell the system to stop turning, they will turn over on itself.

Jake to the rescue AGAIN!  Thanks for your contributions.

[VA FLYER]

1 hour ago, Jake@BevanAviation said:

If the aircraft is banking more than the standard rate turns (approximately 20-22deg bank), that sounds more like a AI issue.  When this happens if you tell it to turn right 90 deg it will continue to turn right until you tell it to stop, they are overly aggressive in commands due to the missing information from the AI to limit the response of the autopilot.  If you don't tell the system to stop turning, they will turn over on itself.

Jake,

Thanks for the reply. The excursions happen from s/l cruise. The AI is a Castleberry unit that was installed when I bought the airplane. It has a manual caging knob which I exercised even though it appeared to be fully operational. The flight director seems to be working normally too.

Tim

[Jake@BevanAviation]

@VA FLYER I have seen a couple of Castleberry electric replacement AI's have issues with solder joints that have caused this same behavior.  If it was me I would be checking the AI on the bench and looking at the output.  The FD bars are a representation of what the flight computer is commanding.

[VA FLYER]

5 hours ago, Jake@BevanAviation said:

@VA FLYER I have seen a couple of Castleberry electric replacement AI's have issues with solder joints that have caused this same behavior.  If it was me I would be checking the AI on the bench and looking at the output.  The FD bars are a representation of what the flight computer is commanding.

Jake,

Are these AIs worth repairing, or would I be putting a Band-aid on a bullet wound? Can it be done in the field?

Tim

[Jake@BevanAviation]

@VA FLYER I would assume someone would have to get approval from Castleberry if it was still under warranty to try and repair the issue.  The instance I had was the AI would intermittently loose the roll output signal.  I removed the AI from the aircraft and put it on the bench, gave it some excitation for the outputs to work, put it in a constant bank around 10 deg and monitored the output.  Without influencing the AI I could see the signal drop out and come back after some time.

This was in a Duke with a Century 4 and a replacement electric Castleberry AI for the Century 4 system.  A shop in Florida had spent months trying to figure out the issue but with it being intermittent some flights were great, other not so much. The main issue was randomly it would start a oscillation chasing the heading bug but the longer the oscillation went the more drastic the banks would get.  As the oscillation continued the aircraft would be doing large s-turns chasing the heading bug at a very aggressive bank.  When the AI signal came back it would stop and track the heading like normal.

If this sounds close to what you are experiencing I would suggest to have the AI put on a bench and have it double checked for intermittent outputs.  This can also be done in the aircraft but it won't be easy.  If you need a shop to help troubleshoot this issue I would suggest talking to Jason at Freedom Aviation in Lynchburg VA.  I have been working with Jason for years helping them troubleshoot autopilot issues.  If you want to chat about the issue just give me a call.

 

[VA FLYER]

5 hours ago, Jake@BevanAviation said:

@VA FLYER I would assume someone would have to get approval from Castleberry if it was still under warranty to try and repair the issue.  The instance I had was the AI would intermittently loose the roll output signal.  I removed the AI from the aircraft and put it on the bench, gave it some excitation for the outputs to work, put it in a constant bank around 10 deg and monitored the output.  Without influencing the AI I could see the signal drop out and come back after some time.

This was in a Duke with a Century 4 and a replacement electric Castleberry AI for the Century 4 system.  A shop in Florida had spent months trying to figure out the issue but with it being intermittent some flights were great, other not so much. The main issue was randomly it would start a oscillation chasing the heading bug but the longer the oscillation went the more drastic the banks would get.  As the oscillation continued the aircraft would be doing large s-turns chasing the heading bug at a very aggressive bank.  When the AI signal came back it would stop and track the heading like normal.

If this sounds close to what you are experiencing I would suggest to have the AI put on a bench and have it double checked for intermittent outputs.  This can also be done in the aircraft but it won't be easy.  If you need a shop to help troubleshoot this issue I would suggest talking to Jason at Freedom Aviation in Lynchburg VA.  I have been working with Jason for years helping them troubleshoot autopilot issues.  If you want to chat about the issue just give me a call.

 

Thanks very much! That sounds just like what I am seeing. It may be a bit more consistent now, since it misbehaved on a trip this morning. Can’t recall ever wanting something to misbehave before, but that’s better then intermittent failures.

[glenn reynolds]

I sent my unit to sacramento executive autopilot and they rebuilt the unit.  Saved thousands

[VA FLYER]

Thanks to all who responded. I sent the AI back to Castleberry and they repaired it. Reinstalled and everything works as it should, at least it has for the last three hours! This really remarkable part? The charge was under $300.00. (Yes, the decimal point is in the right place.) I can't recall the last time I had ANYTHING done on one of my airplanes for only $300. Kudos to Castleberry! 

[carusoam]

Great follow-up VA F!

Best regards,

-a-

[0TreeLemur]

Glad you had success at low cost!   Congratulations!  The KFC-150 is a heck of an autopilot.

I have been trying to troubleshoot the exact same behavior, except I have an Aspen and its two magic boxes that convert digital outputs to analog for the KFC150.

Today I flew a test flight to take video of my misbehaving system.   Flew two cross countries and it worked perfectly.