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Used HSI, AI troubles and the Dynon Pocket Panel

I'm just starting to fly IFR after 8 years as a VFR-only private pilot.

Our aircraft is legally equipped for IFR, but has a certain weak spot as both the DG (not slaved) and the AI are vacuum driven. The DG has to be readjusted every 20 minutes or so. The AI sometimes works perfectly and on other occasions just tumbles around for an hour or more, despite the vacuum indication being constant.

Okay, to the questions :-) ...

1) An obvious choice to solve both problems would be an Aspen. However, there is no STC for our plane and never will be, as there are only about 15 of the type (ST-10) left. Furthermore, the cost for an Aspen with HSI function would be at or above the maximum amount of money we are willing to invest. Does it make sense to install an used HSI in place of the DG? Which costs are to be expected?

2) Do you have any idea what may cause the AI troubles?

3) Provided the AI can be returned to reliable operation, I think about buying a Dynon D1 Pocket Panel instead of a second "spare" AI. I know it's not certified, but it's only a backup anyway and shows much more than just attitude. Any experience with that?

Thank you for your thoughts.

LOAN Wiener Neustadt Ost, Austria

Dear blueline, this is what i think

(The ST-10 is really a very nice and good looking plane!) A reall classic already.

  • If the vacuum pump is really okay (but i would check that before i take any further action!) then both the AI and DG need an overhaul or replacement.
  • If you can find a used King HSI (with all the necessary parts like the wing magnetometer etc) i think that would be the best solution.
  • The D1 pocket panel should be a pretty good backup, I think, but only if it could be installed at a good position in the line of view. Since it has no air data and shows ONLY ground speed and GPS altitude it can only be a backup for the AI. Have not tried it though. I would try one before i buy it, with the option to return it

I think you should buy a KCS55 slaved compass system, which will come with the KI525 HSI. I sold my entire KCS55 very recently for $2500, and that included TWO KI229 RMIs, TWO KMT112 fluxgates, and other stuff. All in mint condition. It would take about a week to put it all in.

A DG which has to be tweaked every 20 mins is 5x better than those I trained with The only way you will fix that is with a slaved compass system.

Lots of people in the USA are putting in "glass" and are throwing out perfectly good KCS55 systems.

You can pick up a vacuum AI for about $1500, brand new. Less if overhauled. Ask Castleberry Instruments - that is the firm I use for all mechanical instruments and overhauls. The only expensive AIs are ones like the KI256 which are used as the pitch/roll source for a King autopilot.

Shoreham EGKA, United Kingdom

Yes, what Peter sold is what you want! I have a freshly overhauled vacuum AI in the basement ... coast about 500 Euros to do some years ago.


You really don't need an HSI. I'm instucting IFR on aircraft that have vacuum driven AI and DGs which are far worse than what you describe. Get your AI repaired, probably only the bearings need to be changed. Shouldn't be too exensive, a couple hundred Euros is what they usually charge.

Some kind of modern solid state attitude reference as backup is certainly a good idea. Who cares if it is approved or not. Personally, I would prefer a "Levil AHRS" or similar with WLAN connection and use it together with an iPad or Smartphone, simply because it can be used with other aeroplanes as well.

Happy landings max

EDDS - Stuttgart

what next, I do not agree. The Dynyon D1 - if attached to the panel or glareshield - is a much better choice than having an AI on an iPad. I for one would definitely not want to fly in IMC with an ipad on my knee. It could ONLY work if the ipad was vertical and in the line of sight, but i know no airplane that has room for that. And strapped to you leg, or even loose, it's probably easier and less dangerous to fly "partial panel". (And this says somebody who owns all iOS devices and has apps in the appstore, so no prejudice here ...)

I for one would definitely not want to fly in IMC with an ipad on my knee...

You are right, on the knee it would not be very useful. I was thinking about our installation using a holder at the side (but we use it for the Jeppesen plates mainly). For us it is important that it is a "removable installation" in case of an inspection - everything attached to the panel and wired to the aircraft electrics would be an unapproved fixed installation.

EDDS - Stuttgart

Thank you for the helpful replies. I'll keep an eye open for a KI525, the AI was to be inspected ASAP anyway.

I sold my entire KCS55 very recently for $2500

Damn, a few weeks too late :-) ...

LOAN Wiener Neustadt Ost, Austria

US Ebay

A lot of the stuff there is obviously junk but...

Also the stuff comes up in the For Sale sections on the big US forums; Pilots of America, BeechTalk, and no doubt others I don't know about.

Shoreham EGKA, United Kingdom

Damn, a few weeks too late :-) ...

But there might be another one coming on the market soon ;-) Should know in about two weeks time.

Dynon D1

I cannot comment from personal experience but I was looking at one, too. The feedback I got from a few guys in the US who use this as back-up "removable" was pretty good through-out though.

EDML - Landshut, Munich / Bavaria
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