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Can an STC override more basic legislation?

Keep in mind one thing, TSO ‘only’ demonstrates functionality. It does not assure that the hardware or the software are adequately designed to be acceptable in your design. So I go back to my first post: TSO eases, to some extent, certification effort for the TC/STC applicant, but it is not a panacea. You can live perfectly, as designer, with no TSOd equipment.
In some cases it will make no sense to use a non-TSO product, in some other cases it willl be a perfectly sensible decision, at least for big design organizations. In the recent past I’ve been involved in certification of systems with a lot of non-TSO stuff.

LECU - Madrid, Spain

My understanding is that TSO is almost never actually required, but the equivalent compliance is must be demonstrated, according to the situation, by an examination of the design of the product.

For example if -40C to +50C is required, the DER will need to look at the parts used and check all their temp ranges, and if say the CPU is -25C to +85C then that’s no good. Obviously the work depends a lot on how much help you get from the manufacturer of the item. Often you get zero…

Years ago I looked at an STC to formally mod the notorious King servos, to make them brushless – a fairly straightforward and fun electronic and mechanical project, using a stepping motor and a gearbox. The current servos are rated down to -55C which is not only stupid in the usage context but is a helluva challenge on component choice. It is no doubt the reason why King and everybody else uses the crappy and nasty Globe and similar motors; they have the magic “-55C” on their spec sheet. Anyway, no TSO would be required but some equivalent would have to be demonstrated.

Buying a TSOd product saves the DER (or EASA 21 company, etc) having to spend time on that part. They can just “plug it in” into their STC application.

So let me narrow it down a bit. How would you go about certifying an autopilot whose user interface is a handheld aviation GPS, say a Garmin Aera 660? I can see a slight improvement in the environmental specs, but the software QA is unknown and very likely nonexistent, and if it existed then Garmin will likely not be willing to discuss it, so you won’t be able to assume anything.

We kind of did this here but without any conclusion because nobody knew what Flight Design did. But they went bust anyway…

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Let me take one example. How would you go about certifying an autopilot whose user interface is an Ipad?

This is a specific case that probably would very difficult (impossible?) to certify. You can find more, sure.
The question, basically, is that with a TSOed equipment you (the designer) only needs to certificate the installation/integration. That’s why I said that TSO eases the job of the designer of the TC/STC. But you can try to certify your design with any non-TSO equipment. It will be more work, and sometimes it will be really difficult because you’re trying to use a piece of equipment that cannot comply easily with certification requirements.

For a small/medium design organization is much better, in general, to go directly for the TSO’ed equipment. For a big organization, sometimes it could be worthy to take the other approach. In any case, and that’s what I wanted to highlight in my previous post, the possibility is there.

LECU - Madrid, Spain

Peter wrote:

The DER would need to ensure stuff like environmental compliance, which he would not be able to do on temperature range grounds alone.

In that case, he or his customer would need to rent access to the right test facilities. I’m about to start EQ testing on something that didn’t exist even on paper a year ago, and the designers have never done anything like it before

Last Edited by Silvaire at 20 Mar 15:11

Peter wrote:

Years ago I spoke to a Honeywell/King guy about the KSN770 who told me that it was originally developed by a subcontractor but the subcontractor forgot to follow software QA processes so even though it worked, they could not certify it.

With good reason. “Worked” and “worked reliably” are not the same thing.

ESKC (Uppsala/Sundbro), Sweden

The DER would need to ensure stuff like environmental compliance, which he would not be able to do on temperature range grounds alone.

I have come across this years ago when somebody certified a kettle, for making tea on a King Air. I don’t think the kettle was modified (except it was 110V) but the job wasn’t cheap.

As regards other requirements for interfacing to avionics, e.g. software quality assurance, I don’t know what the regs are in light GA. @ncyankee and @wigglyamp might know. Years ago I spoke to a Honeywell/King guy about the KSN770 who told me that it was originally developed by a subcontractor but the subcontractor forgot to follow software QA processes so even though it worked, they could not certify it. And this was a navigator, not an autopilot.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

How would you go about certifying an autopilot whose user interface is an Ipad?

For the sale of discussion let’s say a DER completed an 8110-3 including an iPad. Would that not do it? The only issue is that he wouldn’t likely that because it’s not suitable for that job, regardless of TSO status.

But there is no problem at all to certify a design using non-TSO equipments.

Let me take one example. How would you go about certifying an autopilot whose user interface is an Ipad?

Administrator
Shoreham EGKA, United Kingdom

TSO only eases the certification work for the TC/STC applicant. But there is no problem at all to certify a design using non-TSO equipments.

LECU - Madrid, Spain

Peter wrote:

I think that’s different – because they get approved under the airframe manufacturer’s TC.

The TC is a government controlled document that can be supplemented by anybody, under the same requirements as the holder of the base TC, if that organization still exists. I don’t think the original airframe manufacture has special status in relation to the TC, at least not under FAA regs. If an STC is added to a TC the combination is in effect, the additional process is subject to the same technical requirements as the original data and I don’t think anybody involved gets any special treatment.

BTW, before the odd (and rather perverted ) current trend of having STCs to perform simple equipment installations came along, an STC was for only significant changes to the design, by anybody. That is part of the reason why the entire package is subjected to approval, an STC was never intended to be slightly more than a minor mod, using TSO approved off the shelf parts.

Last Edited by Silvaire at 19 Mar 14:28
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