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Latest on KI256 substitution

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I can’t see how “these things aren’t cheap, They tend to cost a few k upwards” reconciles with “Most of my KI256s lasted only about 500hrs. I have a shelf spare.One needs to have shelf spares of these items, to avoid significant downtime.”

Shelf spares of a 25k list price (, 6k pre-owned part that fails every 500h max? A part linked to a vacuum pump that also fails every now and then?

Sorry the math doesn’t add up. For 6k you can get two Garmin G5s, that will fail too but surely not every 500h. For 15k you can get the GFC500 and associated servos on top of the 2 G5s.

As usual, the answer is more complex. For an HBK (Honeywell / Bendix King) autopilot source, to replace a KI256 you need a certified pitch/roll source (LVDT emulation) such as the EFD1000+EA100 or the G500+GAD43 or a G600. So there is no easy way to escape the KI256. A typical repair of a KI256 (bearings) costs a few hundred £. Also only some oddball KI256s cost 25k.

There is an obvious business case for a KI256 replacement and a number of firms have got near doing one (e.g. Sandel have 99% of it already) but none have bothered, except the above two solutions (Aspen or Garmin) both of which have significant challenges. Honeywell itself has predictably abandoned the KI300 which would have been ideal.

Shoreham EGKA, United Kingdom

Peter you’re not hearing me. For the price of two used KI 256s you can get a full system including AI, HSI, autopilot and servos.

If you don’t want a full system, a G5 is about 3k (new-in-box) plus a GAD29B at 500USD are still less than one (used) KI256.

The BK link shows the most plain vanilla, non oddball KI 256 – if it doesn’t kindly explain in which way it is oddball.

So please run me through the math again of how and why two KI256 make sense cause it still doesn’t compute. Maybe it’s a slow Sunday for me, and remember I’m not versed in anorackery..

You don’t need math – a G5 can presently not replace a KI256 as an attitude source for Bendix autopilots. That is the major problem/wish.The GAD29B only helps to get the heading bug of the HSI connected.

@Sir_Percy – sure, but that’s a certification issue pending resolution, not a hardware issue. The capability is there since the G5 provides (certified) AHRS input to the GFC500.

The math still remains valid, 15k for a twin G5+GFC500 system still remains cheaper than 2 (even second hand) KI256. Especially so as it gives full reversionary capability without having to go to the shelf and exchange the duff AI out… Alternatively – – AI, autopilot, transponder & engine monitor in one, for 16k.

Latest price for a KI 256 at Spex is what? 17k without core exchange?

Last Edited by Shorrick_Mk2 at 17 Sep 10:30

I am not sure – I have not read anything or seen an installation manual for the GAD29B which states that it will provide the necessary analog hardware signals to drive a legacy autopilot with attitude information …
Using the GFC 500 is a completely different story – I suspect they will stay in the CAN world which will make it a lot easier.

Concerning maths:

2 G5 + GFC 500 = 15K
Removal of old sytem = 2K?
Installation: Panel work for 2G5 + GFC500 computer+ 2 servos + autotrim = 5-10K?

2 used KI 256 at 1-2k each

As much as I would consider to upgrade to your suggested combo (and I will hardly try to convince myself once my units are dying – believe me ) the math currently simply doesn’t work out.
If only my HSI dies the exchange to the G5 would be an absolute no brainer.

P.S. And the GFC500 has to be certified for my airframe first …

And the GFC500 has to be certified for my airframe first …

Yeah, that little problem Autopilot STCs for say a TB20?

Every KI256 is tied to an autopilot. You won’t have one otherwise (well, sometimes the pitch/roll are used for tilt compensation on a wx radar, hence the KI256 Mod 11).

which states that it will provide the necessary analog hardware signals to drive a legacy autopilot with attitude information …

It isn’t quite just analog signals. To emulate a KI256 you need to emulate the LVDT coils. The autopilot sends a 400Hz (actually more like 500 in the KFC225 – another story) signal to the middle coil and then decodes the returned signal from the other two. This is done for each of the two axes.

This is a fun project for an electronics engineer. AFAIK the GAD43 works by taking in ARINC429 pitch/roll signals from the AHRS module and emulates the LVDT. But you need to certify the whole thing as a primary AI and with a power backup for the specified time. The fact that if you lose electrics you also lose the autopilot doesn’t help you.

Castleberry sell a TSOd KI256 replacement which is electric but that doesn’t help a lot unless you have two alternators etc. They are the company which used to make the KI256 for King in their early days.

Shoreham EGKA, United Kingdom
Shoreham EGKA, United Kingdom

The Aerovonics AV30 with their APA10 adaptor is supposed to emulate a KI256.

The catch? It is uncertified

And the other catch is that the APA10 doesn’t exist

Shoreham EGKA, United Kingdom
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