HSI not aligned with mag compass

[redbaron1982]

I've noticed in the last weeks that my HSI is not aligned with the mag compass.

The HSI is a BK KI 525A. The HDG flag is out of view and slaving is active.

I flew different headings and the difference is not always the same, seems to be worse flying west (+15 degrees diff with compass), a little bit better (+7) on north/south headings and finally flying east there is not difference between the HSI heading and the mag compass.

I was flying straight and level.

Also, looking at the track in FF, I would tend to agree that the mag compass is reading correctly and the issue is with the HSI.

Any idea what can be causing this?

[philiplane]

when was the last time the HSI was calibrated? It should be checked every two years. The remote compass and the HSI require regular inspections to ensure accuracy.

[LANCECASPER]

35 minutes ago, redbaron1982 said:

I've noticed in the last weeks that my HSI is not aligned with the mag compass.

The HSI is a BK KI 525A. The HDG flag is out of view and slaving is active.

I flew different headings and the difference is not always the same, seems to be worse flying west (+15 degrees diff with compass), a little bit better (+7) on north/south headings and finally flying east there is not difference between the HSI heading and the mag compass.

I was flying straight and level.

Also, looking at the track in FF, I would tend to agree that the mag compass is reading correctly and the issue is with the HSI.

Any idea what can be causing this?

I'd look at the KG102A remote gyro. I had those symptoms early on when I bought an airplane in 2015. I sent it up to Porter Strait up in Tulsa and asked for an Inspect and Repair as Necessary. The very fair repair back in early 2016 was around $320 plus shipping

.

[redbaron1982]

51 minutes ago, philiplane said:

when was the last time the HSI was calibrated? It should be checked every two years. The remote compass and the HSI require regular inspections to ensure accuracy.

I have own the airplane for 2+ years now and AFAIK it was never calibrated.

40 minutes ago, LANCECASPER said:

I'd look at the KG102A remote gyro. I had those symptoms early on when I bought an airplane in 2015. I sent it up to Porter Strait up in Tulsa and asked for an Inspect and Repair as Necessary. The very fair repair back in early 2016 was around $320 plus shipping

.

Thanks for the advise, I'm going to look first around Houston and if I don't find anything I'll send it to them or Bevan. 

[LANCECASPER]

25 minutes ago, redbaron1982 said:

I have own the airplane for 2+ years now and AFAIK it was never calibrated.

Thanks for the advise, I'm going to look first around Houston and if I don't find anything I'll send it to them or Bevan. 

@Jake@BevanAviation can probably diagnose which components need to be repaired by the symptoms you mentioned.

[Jake@BevanAviation]

I would start by double checking the compass system to the wet compass on a compass rose.  That should give you an idea as to which system is off.  If the issue is the KCS-55A compass system, possible components that could be a problem would be the KG-102, KMT-112, KI-525, slaving accessory.  There are adjustment pots on the slaving accessory to help align the system.  The adjustments for the slaving accessory are for N/S and E/W.  If the system was consistently off around the compass card I would say adjust the KMT-112.  If only 2 points (N/S or E/W) were off try adjust the slaving accessory. 

If you need help troubleshooting the system give Ronnie Tucker a call (Onsite Avionics) 713-254-9367.  He is based out of Willis TX and has a mobile service.  If the KG-102 needs to be evaluated contact Jerry at Porter-Strait in Tulsa OK.  Unfortunately, we do not have the capabilities to repair the KCS-55A compass system.

[Fritz1]

yes, check against ground compass rose first, the earth magnetic field sensor under a removable panel in one of your wings, you can rotate it to align the HSI with the fluid compass and/or the compass rose, I had an earth magnetic field sensor in a 182RG die on me completely a couple of years ago, wheatstone bridge in there, one of the resistors was burnt out.

[redbaron1982]

On 6/20/2024 at 7:59 AM, Jake@BevanAviation said:

I would start by double checking the compass system to the wet compass on a compass rose.  That should give you an idea as to which system is off.  If the issue is the KCS-55A compass system, possible components that could be a problem would be the KG-102, KMT-112, KI-525, slaving accessory.  There are adjustment pots on the slaving accessory to help align the system.  The adjustments for the slaving accessory are for N/S and E/W.  If the system was consistently off around the compass card I would say adjust the KMT-112.  If only 2 points (N/S or E/W) were off try adjust the slaving accessory. 

If you need help troubleshooting the system give Ronnie Tucker a call (Onsite Avionics) 713-254-9367.  He is based out of Willis TX and has a mobile service.  If the KG-102 needs to be evaluated contact Jerry at Porter-Strait in Tulsa OK.  Unfortunately, we do not have the capabilities to repair the KCS-55A compass system.

Thanks, Jake!

I did the procedure today and I got N/S perfectly aligned, E was already ok, but when I tried to do W the pot was already all the way to the side I needed to turn it. So I was not able to align W.

I guess the next step would be to do the average of all errors and rotate the KMT 112 and re-do the KA 51A calibration. Is that correct?

My second question is, how the **** I get to the tail to rotate the KMT?! I don´t see any access panel nearby. Am I supposed to crowl from the avionics bay down the tail cone to reach the KMT 112?

[LANCECASPER]

I’d still be surprised if it’s not the KG102A

[redbaron1982]

7 minutes ago, LANCECASPER said:

I’d still be surprised if it’s not the KG102A

When in free gyro the heading seems to work fine. That wouldn't rule out the KG102?

[LANCECASPER]

42 minutes ago, redbaron1982 said:

When in free gyro the heading seems to work fine. That wouldn't rule out the KG102?

For how long though?

[redbaron1982]

1 minute ago, LANCECASPER said:

For how long though?

I can do a full 360, stopping at each cardinal point, and getting correct readings while in free gyro mode, while in slave mode I get incorrect readings.

I'm quite sure the issue is with the slaving rather than the gyro. Now, wether if it is just a calibration issue or a component failing, or in the latter, which component is failing, I don't know.

[LANCECASPER]

8 minutes ago, redbaron1982 said:

I can do a full 360, stopping at each cardinal point, and getting correct readings while in free gyro mode, while in slave mode I get incorrect readings.

I'm quite sure the issue is with the slaving rather than the gyro. Now, wether if it is just a calibration issue or a component failing, or in the latter, which component is failing, I don't know.

I was referring to straight and level cross country.

The remote gyro (KG102A) will precess  in free gyro mode just like a DG will. If on the same heading it precesses much over a few minutes the gyro needs some work. From what I've seen in over thirty years of using the KCS-55 system, the KG102A is the most prone to failure.  But we'll see.

Before I would spend more than just a IRAN on the remote gyro (a few hundred dollars), I would consider investing in a G5 or GI275 to replace the HSI.