HSI GS Issue

[poadeleted20]

What we've got is a KPI-series Bendix/King HSI (electric, slaved). The GS needle reads half-scale higher than it should. Other than being half-scale high, the HSI GS indicator does track the GS. When the GNS-530 to which it is connected goes through its power-up tests, and the GS needle is supposed to be half-up, it's full up. In flight on the ILS, it reads half-scale higher than the GS on the #2 CDI which is hooked to a KX-170B, and the #2 is confirmed accurate.

First, any ideas on what's wrong?

Second, any recommendations on an avionics shop to fix this within 200nm of Erie PA?

 

[TangoWhiskey]

Could be the 530; can you drive the HSI / GS from a different source, to isolate if it's the signal source or the indicator itself at fault?

Look at the GNS530 installation manual for a few ideas...

EDIT: Actually, it looks like the maintenance manual is the one you'd need for troubleshooting / calibrating the indicator.

 

[wsuffa]

Could be the 530; can you drive the HSI / GS from a different source, to isolate if it's the signal source or the indicator itself at fault?

Look at the GNS530 installation manual for a few ideas...

EDIT: Actually, it looks like the maintenance manual is the one you'd need for troubleshooting / calibrating the indicator.

IIRC, there's a way to calibrate. It could be anything from a bias voltage on the indicator input to something wrong. It could be either the GNS or the indicator input.

 

[COFlyBoy]

Could it just be a dirty connection? I think those are still analog connections, so a little crud could throw it off.

Side note: The shop that put in our 420W in January grounded a pin that should not have been grounded. This manefested as the GPS unit getting an erronous reading from the OBS. It was off by 30 degrees in some places and dead on in others. Point being, I'm not convinced that whatever is wrong will be all that obviously connected to the symptoms.

 

[poadeleted20]

First thing tomorrow we're going to try reseating the plugs on the back of the HSI.

BTW, it's a KCS-55.

 

[COFlyBoy]

First thing tomorrow we're going to try reseating the plugs on the back of the HSI.

BTW, it's a KCS-55.

Its worth a try. Worked on my autopilot, and its free (or as close as it gets in aviation)

 

[gismo]

First thing tomorrow we're going to try reseating the plugs on the back of the HSI.

BTW, it's a KCS-55.

I don't believe that reseating connectors on your HSI will cure your specific problem but it won't hurt anything either. I think there is a gain adjustment in the HSI (might actually be in the remote gyro). This adjustment shouldn't need attention once it's set properly but it's not uncommon for the adjustable component to go bad (high wiper resistance) in a way that could cause the gain change. Any decent avionics shop should be able to troubleshoot this and the fix ought to be relatively inexpensive.

 

[poadeleted20]

Word we got on the phone this morning from an apparently very knowledgable shop is that this is a common problem with KCS-55's, and requires internal adjustment, i.e., remove, ship, wait, reinstall. But I'm still going to try reseating the plugs.

 

[dmccormack]

Just saw this, Ron. Good shop near KERI is Grove City (very close, actually).

New Philadelphia, OH (KPHD) has a good shop as well (and Garmin Dealer).

 

[poadeleted20]

Spoke with the folks at Grove City. They said if reseating didn't fix it, all you can do is pull it and send it to a component repair shop, which they aren't. And we checked it on an LPV approach today, and the error is independent of data source, so it's pretty obviously internal.