AI and HSI error help

[Ftlausa]

Looking for some insight on an instrument error I had in flight yesterday.  Midway through my flight with the AP engaged (KAP 150), I noticed that both the AI and the HSI were giving erroneous readings.  The AI was indicating a 10 degree left bank, and the HSI was indicating about 10 to 15 degrees left of course.  Back-up AI and turn coordinator were level and vacuum suction was strong, and back-up vacuum pump had no impact when I engaged it.  Even with these readings, the AP held the course.  After I turned the AP off, both indications came back to normal. 

On return flight (VFR), I replicated the error flying with the heading bug with the AP on, but when I switched to NAV mode on the AP, the error went away and it tracked the GPS course.  To confound the problem (thinking that it was probably an AP issue based on the above), the error returned while hand flying in the pattern for landing. 

AI? HSI? AP? Gremlin?            

[ArtVandelay]

Stec APs use TC to determine bank, what does the KAP 150 use?

[Oldguy]

I believe the KAP 150 gets roll and pitch from the AI.

Since the HSI is electric and the AI is vacuum driven, it sounds like a call to Autopilots Central in Tulsa would be in order except for your experience when hand flying. Still, they could probably give some insight to the problem.

For just a general understanding of the different autopilots (as of a few years ago), I find this article enlightening. http://www.avionicslist.com/articles/autopilots.php

 

[Ftlausa]

KAP 150 gets roll and pitch from the AI.  Working theory is that its the AI failing.  But I thought I would solicit some collective wisdom before dropping one or two AMUs on an overhaul or exchange. 

[kmyfm20s]

It's the AI or vacuum that's failing. When my AI failed I could still use the KAP autopilot by offsetting the heading bug in the opposite direction. When in NAV mode the offset being done internally. The lesson I learned is that a vacuum failure is not doom and gloom with the KAP when The IFR.

[peevee]

31 minutes ago, kmyfm20s said:

It's the AI or vacuum that's failing.

we're having AI and or vac issues also, and I haven't experienced a vac failure but my research leads me to believe that vac pumps don't tend to fail gradually, the pumps basically implode and fail when the carbon vanes let go, unless there's maybe something else going on like a failing hose. I'm curious what other people have experienced.

[kmyfm20s]

I would replace the vacuum at the same time, check the lines and put in a filter. I had my AI rebuilt then 20 hrs latter it failed again. I figured it would be covered under warranty but it wasn't. They said it was contamination most likely from carbon from the vacuum. Sure enough we where able to clean some dust out of the line and still had adequate vacuum levels.

[peevee]

39 minutes ago, kmyfm20s said:

I would replace the vacuum at the same time, check the lines and put in a filter. I had my AI rebuilt then 20 hrs latter it failed again. I figured it would be covered under warranty but it wasn't. They said it was contamination most likely from carbon from the vacuum. Sure enough we where able to clean some dust out of the line and still had adequate vacuum levels.

ouch, I don't know about yours but ours is 2k. That's a lot to do, twice. Thanks for the warming.

[Awful_Charlie]

Yup - put a filter as close as is practical to the pump, then when the pump disintegrates (as they do), replace the pump, the filter and everything in between. If you have the standby pump in the tailcone you don't want to have to rip out all of the interior to be able to replace the pipe there!

[kmyfm20s]

This was in my "J" and at the time I was debating if I should put an Aspen in, I wish I did. I don't recall the AI being 2K to overhaul but coincidentally my HSI was was off and had to have it serviced. By the time I was done with the HSI,2 AI's, vacuum pump and filter, I wasn't far off from an Aspen. 

[PTK]

Time to shed some weight and chronic headaches. Take the AI and vaccum system out and put in the latest and greatest:

http://www.bendixking.com/V4/KI-300

[peevee]

7 minutes ago, PTK said:

Time to shed some weight and chronic headaches. Take the AI and vaccum system out and put in the latest and greatest:

http://www.bendixking.com/V4/KI-300

For us, won't talk to our century 41 

[PTK]

7 minutes ago, peevee said:

For us, won't talk to our century 41 

Maybe Century Flight Systems will come up with a similar solution for its APs.

[peevee]

45 minutes ago, PTK said:

Maybe Century Flight Systems will come up with a similar solution for its APs.

Maybe! aspen has an interface, so that's probably an option too, especially if anything ever went wrong with the HSI or flux gate compa$$$$

Maybe someone will make that work with the C-41 in the meantime too, it's definitely a sweet setup at a great price when you're talking 2k for an overhaul. I don't know how common the 41 is, I'm guessing "not very" is the answer.

Edited January 5, 2016 by peevee

[Ftlausa]

The AI was the culprit, and after doing some math, I decided to overhaul the AI for $1,600 instead of $12,000 for an Aspen.  The Aspen is just not in the budget on the heals of the top overhaul last month.   

Thanks for all the replies.

[peevee]

Just now, Ftlausa said:

The AI was the culprit, and after doing some math, I decided to overhaul the AI for $1,600 instead of $12,000 for an Aspen.  The Aspen is just not in the budget on the heals of the top overhaul last month.   

Thanks for all the replies.

thanks for letting us know

[mike_elliott]

 

Time to shed some weight and chronic headaches. Take the AI and vaccum system out and put in the latest and greatest:

http://www.bendixking.com/V4/KI-300

Here we go again.......