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Secondhand autopilot, and STC permission

Unless there is some special FAA policy for autopilots of which I’m not aware, the work on an N-registered aircraft would be documented by a simple A&P logbook entry. I don’t believe a 337 would properly be filed because the installation is not a modification from the type certificated configuration that is already FAA approved, and therefore does not require IA inspection. Perhaps there is such a special FAA policy applicable to autopilots but it’s nothing I’ve run into previously as an owner.

A 337 reports to FAA when a mod outside of the TC is incorporated, referencing approved data outside of the original TC – such as an STC or 8110-3 prepared by an FAA engineering designee. This is not the case for anything within the original TC, including options like for example optional fuel tank configurations for which the mechanic makes a simple logbook entry after installation and that’s it. I have seen 337s filed for optional fuel tank installations but notwithstanding the modern tendency to file a 337 for ‘anything’ I don’t think it’s necessary.

I have no idea if post-certification manufacturer produced service bulletins are automatically FAA approved data that could or would be referenced by a 337 reporting a modification. I would guess they are not approved data otherwise you’d effectively have a manufacturer doing the work of FAA and certifying their own products (effectively writing law), but this is beyond my experience. My IA and DAR friends would know the answer and I’ll ask them next time I see them (they are partners in two planes and usually found in the same place)

Last Edited by Silvaire at 19 Apr 16:00

In the FAA world, it is a bit more integrated since the “maintenance world” can provide “design approvals” (Under EASA it is increasingly the case with CS-STAN, but not historically)

The difference between mod-design and maintenance-mod is like an 8110-3 or STC approval vs a form 337 or log entry for reporting installation of a design which is already approved (via 8110-3 or STC or otherwise)

Would you need a form 337 to report a change under an OEM SB?

Antonio
LESB, Spain

A mod under the TC is called an “OEM-mod” but is a mod nonetheless. It is definitely a mod under EASA but design approval comes in the TC, rather than a separate minor mod or STC.

Typically it is documented in an OEM SB, SL, SEB, SK…., but sometimes it is just the basic IPC calling different options.

The point is that it does not need a separate Part-21 design approval process since approved data is already available under the TC and then it is only a Part-M and Part-145 matter.

In the sense that it does not require design approval under part-21 then it is not a mod, but in the part-M and part-145 maintenance sense it is a mod.

Last Edited by Antonio at 19 Apr 15:23
Antonio
LESB, Spain

Antonio wrote:


OEM’s typically integrate the third-party design in the TC, rather than using the STC. They would however use the STC substantiation data for the inclusion, under commercial agreement with the STC holder.

In which case as I’ve posted before installing a used autopilot would be a maintenance operation not a modification.

Silvaire wrote:

If an aircraft was factory equipped with an autopilot also being sold to the aftermarket, did the factory (let’s say Piper) have to submit a copy of the vendor STC permission letter for DAR sign off with the original airworthiness certification package for an individual newly produced airframe?

No, OEM’s typically integrate the third-party design in the TC, rather than using the STC. They would however use the STC substantiation data for the inclusion, under commercial agreement with the STC holder.

Antonio
LESB, Spain

If an aircraft was factory equipped with an autopilot also being sold to the aftermarket, did the factory (let’s say Piper) have to submit a copy of the vendor STC permission letter for DAR sign off with the original airworthiness certification package for an individual newly produced airframe? If so that letter should still exist in the aircraft records. If not, something else applied, I would guess a license allowing AP certification for the type under the Piper TC. In that case, it would equally apply to the type today.

I have all the original certification data for my individual airframe and I’m sure most owners do too. It would be interesting to look at those records for a Piper that came from the Piper factory with a vendor manufactured autopilot, to see if an STC permission letter issued by the vendor to Piper Aircraft for the individual serial number aircraft is among them.

Last Edited by Silvaire at 18 Apr 16:04

Peter wrote:

How is “still around” defined?

I was just responding to your question.

Peter wrote:

What if the STC holder is no longer around, or is not responding?
KUZA, United States

This is very interesting – especially the last part.

Does it mean that you can apply for a field approval, using the content of some STC, not the STC itself (i.e. not referencing its number) without the STC holder’s permission? I have seen this done, on the suggestion of an FSDO inspector who I would think knew the rules.

My 3rd point in my last post above referred to an STC which was basically worthless because it added no value to stuff already in FAA approved IMs etc. This may be academic in the case of an autopilot, which is quite a specific thing and for which (a) and STC is required (unless an OEM installation) and (b) one is not likely to have more than one STC available.

If the STC holder is no longer around, you won’t be able to obtain the permission required by 91.403(d) and will be unable to use the STC as the basis for installation. If the holder is still around, but unwilling to provide written permission to use for an STC they allowed you to use, they are in violation of 21.120 which requires them to provide written permission and you can report the issue to the FAA and likely take civil action to force them to comply or pay damages.

How is “still around” defined?

Administrator
Shoreham EGKA, United Kingdom

If the STC holder is no longer around, you won’t be able to obtain the permission required by 91.403(d) and will be unable to use the STC as the basis for installation. If the holder is still around, but unwilling to provide written permission to use for an STC they allowed you to use, they are in violation of 21.120 which requires them to provide written permission and you can report the issue to the FAA and likely take civil action to force them to comply or pay damages.

From FAA definitions: Maintenance means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance. Replacing a part requires that the part be approved for installation on type certificated aircraft by an authorized person and that meets the part’s airworthiness criteria. Replacing a part such as a servo on an aircraft assumes the original STC was already installed. As long as the mechanic can certify the part is airworthy by an appropriate means such as testing or a form 8130-3, they should be able to use the part. The aircraft already has the STC permission. The mechanic would have to confirm the suitability of the part and so on. Some manufacturers don’t provide maintenance manual data to determine if the part is airworthy, in which case the part would need to be returned to the manufacturer for overhaul or airworthiness determination.

Your third point suggests a misunderstanding of the use of an STC. It is FAA approved data developed by the STC holder and provides the basis for installation of an item on a certified aircraft. It is a modification to a TC. For example installing a different engine in an aircraft other than the one on the TC may be installed using an STC as the legal basis for the modification. Multiple STC from separate companies may each provide an independent basis to install the engine. If you have the written permission of one of the STC holders to use their data to install the engine, you may modify the aircraft using their STC. Or, you could get a field approval to install the same engine and not use either of the STC’s. IOW, the installation of the engine requires FAA approved data which may be provided by STC or other means. It is not proprietary to install the engine, it is proprietary to install the engine on the basis of a given STC holder’s data. Using an STC to obtain the FAA approved data and basis for the installation is often cheaper and quicker than developing your own FAA approved data using a DER and field approval process. Look at this FAA General Counsel Opinion that relates to the subject:

KUZA, United States

You can’t install any STC without the explicit permission of the STC holder.

The questions which remain are:

  • What if the STC holder is no longer around, or is not responding? With books and such there is the copyright expiry time (very very long)
  • What if the installation is only partial (e.g. only replacing autopilot servos)? This is a very similar thing to the widely established exhaust “repair” industry where you avoid having to get an STC or a PMA, by getting the customer to supply one tiny part of his old exhaust and you build him a completely new one (probably not even bothering to include that bracket )
  • What if the STC is a “bogus” one i.e. everything in it was previously covered by stuff in IMs, covered by a previously approved mod, etc? It is easy to get an STC for something which is wholly prior art, and a lot of STCs are like that. The FAA or EASA are not going to check for prior art, in the way the Patent Office does and you can still get a patent for something with prior art all over it, if sufficiently specialised. Controversial, because the STC holder was probably well aware, but was still hoping to make some money out of it. For any given proposed installation, there are likely to be a whole pile of old field approvals, IM circuit fragments, stuff in AC43-13 (structural stuff is a ripe area for STCs which an installer can get the client to pay for, but actually the procedure was in AC43-13 all along), in EASA-land you have the option of grandfathering a mod from any other EASA country and many of those require a considerable effort to find…
Administrator
Shoreham EGKA, United Kingdom
58 Posts
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