KAP 150 Issue

[JHillier]

Hi all,

Bought my first airplane about a month ago. 1982 J Model with a KAP 150 and KG 258. Looking for some input as to what is considered normal, and or something that needs adjusted. Autopilot all works reasonably well but I have noticed in Nav mode it stays about a 1/4 deflection right of course and it seems to be continually hunting. Reviewing Foreflight track log data wings are consistently going back and forth about +/- 3 degrees and is very evident in flight. Is there any sort of adjustment that can be done to tame the oscillating wings in cruise? Thanks!

 

Jared

[Z W]

Hello, welcome, and congratulations on the new plane.

After spending thousands of dollars trying to fix random errors like this on our old KAP 150, and discovering there are really not many shops left with any knowledge or experience on how to fix them, we determined the best repair was to replace it with a Garmin GFC500 autopilot. Jefferson City Flying Service in Jefferson City, Missouri is near you and put ours in and it has been great. Really transformed the plane.

If hunting +/- 3 degrees on heading is all yours does it is probably working pretty good. The fix will be somewhere in the computer board, your wiring harness, or whatever custom adapter / splice / setup someone did to make your legacy analog autopilot follow a digital heading output from your GPS instead of a VOR or localizer signal (assuming you're flying a GPS). Be prepared to take it to a shop, pay them several thousand dollars to diagnose and try to fix, and have it still do the same thing when you get it back. I'd be curious to know if it shows the same behavior while flying a VOR or localizer track. That might help you pinpoint the problem.

I'd probably run it like it is until a major autopilot component dies or you're otherwise ready to replace the whole thing. It's a solid enough autopilot and sure beats hand flying everywhere, but you may want to lower your standards a bit and always be ready to hand fly.

[Yetti]

Can you run it with a heading bug?    I noticed my STEC 30 with the STec 180 DG was not all that accurate.    When I updated the DG to a AV-30 the tracks are spot on

[JHillier]

In heading mode it does about the same seemingly matches the heading bug then drifts off right a bit then corrects back over and over 

Edited Tuesday at 02:22 PM by JHillier

[LANCECASPER]

4 hours ago, JHillier said:

Hi all,

Bought my first airplane about a month ago. 1982 J Model with a KAP 150 and KG 258. Looking for some input as to what is considered normal, and or something that needs adjusted. Autopilot all works reasonably well but I have noticed in Nav mode it stays about a 1/4 deflection right of course and it seems to be continually hunting. Reviewing Foreflight track log data wings are consistently going back and forth about +/- 3 degrees and is very evident in flight. Is there any sort of adjustment that can be done to tame the oscillating wings in cruise? Thanks!

 

Jared

Maybe in your logs at some point the KG258 attitude indicator was overhauled or replaced. If so, it should have been realigned to the autopilot, which doesn’t seem to get done very often these days.

But this is the guy that will know what’s wrong: @Jake@BevanAviation

Jacob Kinsley   https://bevanaviation.com/location-contact/

[Yetti]

10 minutes ago, JHillier said:

In heading mode it does about the same seemingly matches the heading bug then drifts off right a bit then corrects back over and over 

Then it may be the unit.    But still could be the input.    It was about $5K to do both the Artificial Horizon and the DG with AV-30   Pretty cost effective upgrade if not wanting to do the EFIS thing quite yet. The AV-30 has all the other 6 pack information in one unit.  So redundancy is being added.  

[N201MKTurbo]

22 minutes ago, Yetti said:

Then it may be the unit.    But still could be the input.    It was about $5K to do both the Artificial Horizon and the DG with AV-30   Pretty cost effective upgrade if not wanting to do the EFIS thing quite yet. The AV-30 has all the other 6 pack information in one unit.  So redundancy is being added.  

I just installed an AV-30 in a Cessna. You will need a bunch more stuff to make it work. I’m not sure it will work with the KAP-150. I wasn’t doing an autopilot install, so I just glanced over the autopilot interface. I don’t think it will work with an analog autopilot. I think it will only work with AIRINC autopilot. You will need the AV-30-C, magnetometer, HSI interface (maybe), autopilot interface, and might as well get an OAT probe. Plus figure on 20 - 30 hours for install.

[Rick Junkin]

5 hours ago, JHillier said:

I have noticed in Nav mode it stays about a 1/4 deflection right of course

This is easily adjusted with a flat jeweler's screwdriver through a hole in the faceplate. I was able to get mine centered up by taking a buddy up with me to adjust it while tracking a GPS course. Not a great picture, but the green circle shows you where the adjustment access is.

[Yetti]

26 minutes ago, N201MKTurbo said:

I just installed an AV-30 in a Cessna. You will need a bunch more stuff to make it work. I’m not sure it will work with the KAP-150. I wasn’t doing an autopilot install, so I just glanced over the autopilot interface. I don’t think it will work with an analog autopilot. I think it will only work with AIRINC autopilot. You will need the AV-30-C, magnetometer, HSI interface (maybe), autopilot interface, and might as well get an OAT probe. Plus figure on 20 - 30 hours for install.

Using the AV-APA and the free unlock for the older analog A/P.  See the diagram on p166 of the manual.  page 93 of the manual has the pin outs for the Various Stec autopilots.  I did not install an OAT probe.    The funny thing here is there is a jumper in the Stec 30 that you have to install to make it like a KAP-150.   Mine had already been converted. 

If you have a modern GPS Navigator then would want to use the AV-HSI to grab the ARINC information.   The AV-HSI is also used to talk to a digital A/P. 

[DonMuncy]

12 minutes ago, Yetti said:

Using the AV-APA and the free unlock for the older analog A/P.  See the diagram on p166 of the manual.  page 93 of the manual has the pin outs for the Various Stec autopilots.  I did not install an OAT probe.    The funny thing here is there is a jumper in the Stec 30 that you have to install to make it like a KAP-150.   Mine had already been converted. 

If you have a modern GPS Navigator then would want to use the AV-HSI to grab the ARINC information.   The AV-HSI is also used to talk to a digital A/P. 

You guys make me feel so dumb 

[JHillier]

1 hour ago, Rick Junkin said:

This is easily adjusted with a flat jeweler's screwdriver through a hole in the faceplate. I was able to get mine centered up by taking a buddy up with me to adjust it while tracking a GPS course. Not a great picture, but the green circle shows you where the adjustment access is.

Was your aircraft also oscillating in the roll axis as I described, or did this just fix it centering up the CDI?

[Yetti]

4 minutes ago, DonMuncy said:

You guys make me feel so dumb 

We just read the manual so you don't have to....      There was lots of digging and Google FU involved.        The Stec 180 has a remote mount gyro in the Comm Bay.    So using the Pin outs for gyro, I was able to install the AV-MAG remote magnetometer in the Com bay and reuse one of the shielded wires back up to the front.     

[N201MKTurbo]

14 minutes ago, Yetti said:

We just read the manual so you don't have to....      There was lots of digging and Google FU involved.        The Stec 180 has a remote mount gyro in the Comm Bay.    So using the Pin outs for gyro, I was able to install the AV-MAG remote magnetometer in the Com bay and reuse one of the shielded wires back up to the front.     

How many hours did it take start to finish? Including reading manuals, pitot static plumbing, harnesses, ordering parts and such? And configuring, calibration and paperwork.

[Flyler]

Have you checked the "low hanging fruit" first? I'm not sure if your KAP150 is like my C41, but I've found a lot of information regarding loose/weak connections.  Found a corroded pin or two, and even a broken wire.  Fortunately at easily repaired locations (like the DG).

I would do some unobtrusive and low cost inspection before going nuts. If you were to adjust a pot to compensate for a poor signal, and then later on you replace your DG or even just reset the connector... Now the signal is stronger... Your adjustment is overcompensating... I hope that makes sense.

[Yetti]

2 minutes ago, N201MKTurbo said:

How many hours did it take start to finish? Including reading manuals, pitot static plumbing, harnesses, ordering parts and such?

8 Hours to build the wiring harnesses. While reading the manual.  Wire/Connectors was from the big box of wire from other projects.    Put a couple of hours down to research the AV-30 and STec 180 horizon.   Which are for sale if anyone needs one. 

Hour to fab and paint the 3" square to round adapter.  Had to go to Home Depot and buy a 3" hole cutter.

Install was probably 5 hours.   Mistakes were made, rework had to happen. 

Hour to do the 12 points AV-MAG spin the plane around to calibrate.

Hour for Documentation/WB stuff.    Note here this can be installed under signature vs 337

https://drs.faa.gov/browse/excelExternalWindow/E05E88EEEDAED8A886257FA40060E9F9.0001%3FmodalOpened%3Dtrue?modalOpened=true

Not including the drive to Houston because I could not find the mini pins.  Needed for install into the STEC 30 A/P harness.  Did not know I needed them till I saw the connector.  I had them just could not find them.

Obviously the next one would go much faster.   Probably half the time.    Also remember I have a Dynon install under my belt and installed two way radios to put myself through college.   And I still install radios in the fire trucks along with lights and such.   We never get away from our roots. 

About ~$7K to uAvonix for all the parts.   

Just got notice from uAvonix about their Tablet route planning integration.   https://uavionix.com/press/uavionix-brings-foreflight-integration-and-autopilot-coupling-to-certified-aircraft-with-av-30-c-3-2-1/?utm_source=Klaviyo&utm_medium=email&utm_campaign=AV-30-C 3.2.1 Release&_kx=OuycC-b-6keUgxOfMCiu-WtF9omezaBgYtsr9SB0Z7w.WVJGJJ

 

 

 

[Yetti]

8 minutes ago, Flyler said:

Have you checked the "low hanging fruit" first? I'm not sure if your KAP150 is like my C41, but I've found a lot of information regarding loose/weak connections.  Found a corroded pin or two, and even a broken wire.  Fortunately at easily repaired locations (like the DG).

I would do some unobtrusive and low cost inspection before going nuts. If you were to adjust a pot to compensate for a poor signal, and then later on you replace your DG or even just reset the connector... Now the signal is stronger... Your adjustment is overcompensating... I hope that makes sense.

yes.  Reseating it in the tray should be the first step.   

[N201MKTurbo]

5 hours ago, Yetti said:

8 Hours to build the wiring harnesses. While reading the manual.  Wire/Connectors was from the big box of wire from other projects.    Put a couple of hours down to research the AV-30 and STec 180 horizon.   Which are for sale if anyone needs one. 

Hour to fab and paint the 3" square to round adapter.  Had to go to Home Depot and buy a 3" hole cutter.

Install was probably 5 hours.   Mistakes were made, rework had to happen. 

Hour to do the 12 points AV-MAG spin the plane around to calibrate.

Hour for Documentation/WB stuff.    Note here this can be installed under signature vs 337

https://drs.faa.gov/browse/excelExternalWindow/E05E88EEEDAED8A886257FA40060E9F9.0001%3FmodalOpened%3Dtrue?modalOpened=true

Not including the drive to Houston because I could not find the mini pins.  Needed for install into the STEC 30 A/P harness.  Did not know I needed them till I saw the connector.  I had them just could not find them.

Obviously the next one would go much faster.   Probably half the time.    Also remember I have a Dynon install under my belt and installed two way radios to put myself through college.   And I still install radios in the fire trucks along with lights and such.   We never get away from our roots. 

About ~$7K to uAvonix for all the parts.   

Just got notice from uAvonix about their Tablet route planning integration.   https://uavionix.com/press/uavionix-brings-foreflight-integration-and-autopilot-coupling-to-certified-aircraft-with-av-30-c-3-2-1/?utm_source=Klaviyo&utm_medium=email&utm_campaign=AV-30-C 3.2.1 Release&_kx=OuycC-b-6keUgxOfMCiu-WtF9omezaBgYtsr9SB0Z7w.WVJGJJ

 

Sounds about right.

[0TreeLemur]

10 hours ago, LANCECASPER said:

But this is the guy that will know what’s wrong: @Jake@BevanAviation

^^^  This.   Jake can make an old KFC computer behave like a young KFC computer.

[AndreiC]

I don't know about King gyros, but when I had an older Century autopilot in a Piper I was told that hunting like what you described was caused by an old/tired aileron servo motor. They explained to me that the analog system gives initially small prompts to the servo to correct course, but an older servo has higher friction and/or old brushes, and so it does not react at all at low voltages. As the plane gets more and more off-course (or farther away from wings level), the autopilot increases the voltage to the servo in order to correct more aggressively, until eventually the servo reacts. But now the voltage is higher, and the whole system over-corrects, and gets into a loop. 

This was why when I installed that Century autopilot the installer told me they would not touch it until the servo was sent to Autopilots Central to be overhauled. And indeed, it worked beautifully after it was installed.

[Rick Junkin]

10 hours ago, JHillier said:

Was your aircraft also oscillating in the roll axis as I described, or did this just fix it centering up the CDI?

No, I didn’t have the oscillations. This just adjusts the the steering to center the CDI.

[Will.iam]

20 hours ago, Rick Junkin said:

No, I didn’t have the oscillations. This just adjusts the the steering to center the CDI.

Is that adjustment for nav only or does it effect heading too?

[Rick Junkin]

7 minutes ago, Will.iam said:

Is that adjustment for nav only or does it effect heading too?

Someone smarter than me will need to answer that. It adjusted the A/P steering to center the HSI, so I have to assume the same adjustment affects where it steers in heading mode. But that's an assumption so not worth much.

[Rick Junkin]

On 2/24/2026 at 4:50 AM, JHillier said:

Hi all,

Bought my first airplane about a month ago. 1982 J Model with a KAP 150 and KG 258. Looking for some input as to what is considered normal, and or something that needs adjusted. Autopilot all works reasonably well but I have noticed in Nav mode it stays about a 1/4 deflection right of course and it seems to be continually hunting. Reviewing Foreflight track log data wings are consistently going back and forth about +/- 3 degrees and is very evident in flight. Is there any sort of adjustment that can be done to tame the oscillating wings in cruise? Thanks!

 

Jared

 

28 minutes ago, Will.iam said:

Is that adjustment for nav only or does it effect heading too?

Here's an old thread with more details on a similar situation. The gist of it is it may be better to let someone who knows what they're doing take care of it for you.

 

[Yetti]

On 2/24/2026 at 4:14 PM, N201MKTurbo said:

Sounds about right.

The other thing I did which added some time is instead of using butt splices to connect to the plane Other than power they are all DB-9 connections.   The connection to the KLN89B did not work, but I recently switched TX and RX so when I get out of annual I will test that.    And will probably just swap  it out with a GPS 175, but I really would like to stay away from Garmin.   I have thought about putting a Dynon 7 inch screen in and using it for a Engine and ADSB-in screen along with controlling Transponder and one NAV unit.

[Fly Boomer]

3 hours ago, Rick Junkin said:

Here's an old thread with more details on a similar situation. The gist of it is it may be better to let someone who knows what they're doing take care of it for you.

@Jake@BevanAviation is the man.