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KI256 problems, replacement options, etc

On my last flight with TB, when I did the Aspen pre installation check flight, my KI256 went ( the first time) completely upset. Slowly turned approx right 60-70 degrees to the left and held there. Of course the autopilot test failed, but suddenly all came back to normal. It was in VMC, but since that time, the KI256 is good to be a core for OVH.

Zsolt Szüle
LHTL, Hungary

Peter wrote:

It did it again this week, for some minutes, before correcting itself

Peter, what are the real alternatives, that are certified to work with autopilot? (in EASA land)
G500/G500 TXi with some GAD autopilot adapter?
Aspen EFD1000?
Or some basic HBK $20K solid-state AI that breaks every month?


What I find puzzling (as an engineer) is what mechanism could cause the drift of about 2.5 degrees which then corrects itself. The vacuum reading was fine throughout, at the top of the green arc.

what are the real alternatives, that are certified to work with autopilot? (in EASA land)

Anywhere, FAA or EASA, I think they are the same as for years:

  • G500 + GAD43
  • G600
  • EFD1000 (or some successor) + EA100
  • KVG350 (a large gyro, not practical for light GA)

Probably something in the Garmin TXi range does it also, but nobody I know has any experience of these products.

As regards the KI300 I have just edited that thread to remove yet another dead link from HBK (Honeywell Bendix King) as they abandon one thing after another. They now call it “Aeroflight” and have a full page ad in the US AOPA mag, but that doesn’t mean it exists. It is a rebadged Sandia SAI 340 and it needs the KA310 to emulate the KI256. This page might work for the next 5 minutes

AeroFlight, also known as the KI 300, is a modern, solid-state system that can serve either as a primary or backup attitude indicator. It also has the option for an autopilot adapter, the KA 310, that can control many autopilots, including native support for many BendixKing autopilots.

To be honest the KI256 replacement is not a fish worth frying, unless done as a part of some other refit which is justified on other grounds. You can buy a used KI256 for not much these days and keep it is a shelf spare. That’s what I have. Make sure it is a Mod 11. They seem to last a few years before they fall over and then you just swap it. With decent air fittings it is a quick job. There are firms which will “overhaul” these for a few hundred, just by changing the bearings and not touching anything else.

Shoreham EGKA, United Kingdom

The Aerovonics folks seem to be promising a solution: Legacy Autopilot Integration
Granted it is still vapourware, but their other product did get FAA approval.

EPKP - Kraków, Poland

Yes; came up before here. It’s not hard to emulate a KI256. The actual development is a few months’ work in total. It is just an AHRS (everybody in GA uses an off the shelf module) with LVDT emulation (some signal processing and some op-amps).

Then you just need to get an STC…

Castleberry have a KI256 replica but electric. They have been making it for many years. Unfortunately, while it tests out perfectly in the same test jig used to test a KI256 (Castleberry used to make the KI256 for King) it doesn’t work with a KFC225. This could be because the test jig runs at 400Hz, while the KFC excites the KI256’s LVDT coils at ~500Hz. The KFC225 has, I am reliably told, a config for 400Hz, but I have not been able to find out where this config is. Anyway, an electric replica is no good (legally or practically) unless it either has a big battery or your plane has a second alternator.

Shoreham EGKA, United Kingdom

Peter wrote:

What I find puzzling (as an engineer) is what mechanism could cause the drift of about 2.5 degrees which then corrects itself.
Dust or chips stuck/unstuck in the bearings?
ESMK, Sweden

How long does it stays off at 2.5 degres?

I expect to see some small pitch/bank errors after say 180/360 degres turns but these will go away after few minutes of straight and level flight even with the cleanest AI in the market

ESSEX, United Kingdom

Maybe 10 minutes. It starts by itself in straight and level flight; no turns. The plane remains wings-level because the autopilot compensates by gradually disregarding the duff roll signal (otherwise it could not hold a straight-ahead heading).

Shoreham EGKA, United Kingdom

If the spinning noise is quiet when the engine stops then it is likely related to dirt/vacum issues than mechanical problems from the previous hard landings :)

The formers will be hard to reproduce and fix on the ground

ESSEX, United Kingdom

I’ll use this thread instead of starting a new one;

During straight & level flight (AP KFC150 in ALT & HDG) attitude indicator (KI256) slowly starts to pitch down to -15 degrees. AP reacts with pitch up trim and acft starts to climb. After a couple of ap on/off cycles the pitch up becomes rather agressive. Nothing to do but to handfly the remainder of the flight.

The next flight, same problem

The bank indication is spot on, so only the pitch axis is way off.

I guess I have a bearing problem. Is this something that can be repaired (<1K $) ? I’d like to upgrade to glass, but now is not the time. And I’ll need the KI256 for the AP…

EBST, Belgium
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