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Autopilot certification

I have often wondered how for example STEC have cornered the retrofit market with the 55X (and others) by having STCs for seemingly hundreds of different aircraft.

Against that, Honeywell never did much with their KFC range, approving them for just a handful of types.

The Garmin GFC700 seems to be for the G1000 only.

The Avidyne DFC90 is, like most new stuff from Avidyne, more talk than substance and when I speak to them at shows they make it clear they are going for a very small number of planes only.

I have never designed a plane but do know about control systems theory (from electronics and non-aviation mechanical work) e.g. the traditional PID solution.

It seems obvious that to make sure an autopilot will be stable you need to check it at each of the four corners of the loading envelope, and do that test at all speeds for which the AP's AFMS does not "de-authorise" its use which basically means all speeds from Vref (Vs+30%, minus some margin for safety) to Vne (plus some margin for safety).

There are many reports of autopilots going unstable, and this is even in new planes, so obviously somebody didn't do this properly. Not long ago I flew in a new-ish SR20 which had a 55X and I could not describe that as stable in cruise, with noticeable wallowing around if there was any turbulence.

What are the certification requirements for GA autopilots?

Administrator
Shoreham EGKA, United Kingdom

The Avidyne DFC90 is, like most new stuff from Avidyne, more talk than substance and when I speak to them at shows they make it clear they are going for a very small number of planes only.

That's not true. It receives great praise by pilots and has been available as a Cirrus SR20/22 retrofit for a number of years. The Malibu is also supported and now the Cessna 182. That's already a good list.

I am waiting for an EASA STC for my airplane, the minute it becomes a possibility, I will kick out the S-TEC and install the DFC90.

My assumption is that it used to be easier to get such STCs with less paperwork and testing required.

Peter,

I don't know what issue you have with Avidyne but for me, they are the only way out of the Garmin monopoly and in the case of autopilots of the S-Tec option.

I am considering what to do at the moment as my plane as it stands is not IFR certifiable under EASA, so I'll need to upgrade significantly. Now the question is, do I go the Garmin road with an S-Tec ap or do I wait for Avidyne?

Their 440/540 direct replacements for the Garmin 430/530 series look like a genuine breath of fresh air at competitive pricing and minimal installation cost. Knowing that Garmin will eventually cut support for my 430 1st generation (they have already done so on the 28V version) I am genuinely interested in swapping, possibly for a 440/540 combo to sort out the 8.33 requirement for my com2 as well.

AP, I am not very happy with the recent pricing development with S-Tec, nor with the reports I read. Generally, I'd need a 55X together with an Aspen PFD to get my plane IFR, as I will need both a 2nd Altimeter and HSI and lack the panel space. So why not opt for the DFC90 once it becomes available? Avidyne seems to heavily work with Aspen for the retrofit market.

Achim, the way it looks is your wait may well be at an end: DFC90 EASA certified for C182

LSZH(work) LSZF (GA base), Switzerland

I have a DFC-90 and it is a fantastic autopilot.

EGTK Oxford

I don't know what issue you have with Avidyne but for me, they are the only way out of the Garmin monopoly and in the case of autopilots of the S-Tec option.

I have no personal issue with Avidyne (have just spent £12k on the TAS605 for example, in preference to the Garmin product) and agree re the Garmin monopoly being a very bad thing.

And if you read the US forums there is a very strong feeling that anything should be done to block the Garmin monopoly getting any worse.

However I also think that in this game "we" are shamelessly used as both beta testers and - those asked to put down deposits - working capital providers, and it pays to be a bit "selfish" and go for stuff that is more proven, etc. Also some of the "headline" products are quite unreliable if you speak privately to the owners. And Garmin products are basically pretty good.

For example, you know what I think of Honeywell and the shameless way they have treated KFC225 owners, but I am still keeping my KLN94/KMD550 until I absolutely have to rip them out (basically if enroute PRNAV becomes operationally significant in Europe and is enforced so tightly that there is no way around it, which I hope is a very long time) because they are good solid debugged boxes which do all that is actually required for European IFR.

Does anybody know what is involved in determining the stability margins on an autopilot?

Administrator
Shoreham EGKA, United Kingdom

I don't know the answer to your question, nor do I have a copy, but the current TSO requires compliance with RTCA DO-325, Minimum Operational Performance Standards (MOPS) for Automatic Flight Guidance and Control Systems and Equipment. It can be purchased from RTCA for $187.50. Copies may not be shared so you are unlikely to find it on the internet in PDF form. It is available in PDF form, but is PW protected and I believe you have to sign a non disclosure agreement.

KUZA, United States

What I would be particularly interested in is what data has to be collected to get an autopilot STC.

AIUI, a TSO for the equipment is independent of the STC which allows it to be installed in a particular aircraft type.

The DFC90 and GFC700 do work very well (I flew a TBM850 with the 700, in 2010) but they are not STCd for many aircraft.

Administrator
Shoreham EGKA, United Kingdom

GFC700 do work very well (I flew a TBM850 with the 700, in 2010) but they are not STCd for many aircraft

The GFC700 doesn't have a single STC (supplemental type certificate), it only comes with the G1000 which is not available for retrofit. A shame, the GFC700 would be very popular.

The effort to get an STC must be considerable. The Extra 500 which is built around the Avidyne Entegra R9 still does not have an STC for the DFC90 and ships with a ridiculous S-TEC 55X. There must be something about the S-TEC that makes STC a lot simpler than other autopilots. Maybe because it is an old design for which other rules apply?

On a point of detail the G1000 can be retrofitted but only into some high-end types.

Socata charge $400k for the TBM700 install.

There must be something about the S-TEC that makes STC a lot simpler than other autopilots. Maybe because it is an old design for which other rules apply?

That's why I am asking the question.

Either they did it using some old rules, or they used some "grandfather route" (certify one type and base later "similar" certs on that; it's often done in e.g. EMC compliance in electronics), or they did, ahem, something else

The King APs use a KI256 as the pitch/roll source (together with a pitch accelerometer), whereas STEC use the TC (together with a pitch accelerometer, I believe). The King system produces far better control, and there are no known marginal stability issues, but I can't see it fundamentally harder to certify, other than the possible factory that if you lose the KI256 or the vac pump, you lose the AP also.

Administrator
Shoreham EGKA, United Kingdom

Reading the Avidyne sites, it looks like they need to install and do fairly extensive ground and flight testing on each new type before the FAA will grant the STC. An expensive and time consuming process. I would assume this could be complicated with the DFC-90 due to the s&l button and the envelope protection features.

EGTK Oxford
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