337 or STC for non-primary and/or non-required instruments?

[Hank]

I'm a relatively green pilot (~150hrs) and new plane owner and my plane is just getting buttoned up from an Avionics install that's been in the works for a bit. Now I'm wishing I had had an engine management system installed (at least CHT's/EGT's) but I'm not going to throw that wrench into the works because I need the plane back. Also - my partner is an A&P.

Question 1: If we were to install a standard 4-cyl digital CHT/EGT gauge does that require more than a logbook entry if it's not replacing any required equipment (plane doesn't have a factory CHT gauge)? Does this come down to the A&P determining whether it's a major/minor alteration or am I way off on that assumption?

Question 2 (only applicable if the answer to question 1 is "yes"): If a full-suite engine management system were installed (one that's certified as a primary) is the STC paperwork or 337 technically required if the existing primary gauges are not removed? As in... could the paperwork be deferred until I want to pull the existing gauges and make the gauge the primary? Now that I think about it, it seems this wouldn't work unless there was a way to say that the secondary instrument can't be used as there would be no way to differentiate which was the primary?

Not trying to skirt the rules. Just trying to determine if I can have the gauge (a.k.a. enhanced situational information) in the meantime since it would be many many months before I could schedule to have one installed by a shop. Also if I went with route 2, I would "eventually" want to remove the existing primary gauges, but would want to wait to do that till I do my "phase 2" avionics install which will include cutting a new panel (I really hate the look of holes and disconnected/inop'ed gauges).

There's no such thing as a dumb question right?

 

[Bell206]

Does this come down to the A&P determining whether it's a major/minor alteration

Yes.

is the STC paperwork or 337 technically required if the existing primary gauges are not removed?

Depends. 1st, if you purchase an STC kit and plan to use the STC paperwork to install the kit then you must follow every STC requirement. 2nd, if the changes you make fall under the definition of a major alteration then a 337 would be required regardless of your intent.

There's no such thing as a dumb question right?

No. Unless you ask the same question over and over without learning from the 1st time.

 

[weirdjim]

A LOOOONG time ago, Pacific Region FAA HQ put out a document that is no longer available, but has not been rescinded or superseded. They proceeded to tell us how to differentiate between "major" and "minor". I wish to hell they would send it out again.

Changing engine types is major. Drilling hole in pressurized skins is major. Replacing wings from another type of aircraft not on the Type Certificate is major.

Installing new radios is minor. Changing instrumentation with equivalent types is minor. Almost everything else is minor.

Today's mechanics/IAs are afraid to replace a cotter pin with one a tenth of an inch longer are afraid of the FAA coming down on them for whatever. Cut a tenth of an inch long and put the G0D-d@mn#th!ng in -- IF IN YOUR BEST PROFESSIONAL OPINION it is OK. THat is why we have to not only spend three years getting an A&P, but a lot more before they will give us an IA. That's called professional judgment.

If you don't want to install the kit via the STC, then let the A&P install it under his authority to do minor modifications.

IF, and ONLY IF, this is his/her field of expertise and can do it within their scope of expertise.


Jim

 

[AK737pilot]

My IA's interpretation is that if you install gadget using a Supplemental Type Certificate (STC) then a 337 is absolutely needed because you are changing the Type Certificate, which, in his opinion is a major change. Fortunately for me, he's all too ready to sign just about any 337 I put in front of him.

 

[Bell206]

if you install gadget using a Supplemental Type Certificate (STC) then a 337 is absolutely needed

FYI: considering there are 4 or 5 different types of STCs, each with their own conditions and limitations, it is only a design approval. Whether a 337 is required depends on if the installation falls under the definition of a major alteration. If your IA prefers to fill out a 337 for every STC, that is his prerogative, however, we have had an STC or two posted on PoA that plainly states on the STC document the installation is a minor alteration which by definition does not require a 337.

 

[thomasdr72]

Always fun discussion... I had an airplane that I sold get a full review of the paperwork by an inspector before an export certificate was issued, and basically the text above was the gist of the follow-up conversation. If you install an STC (one of mine was the Rosen Sun Visors) then a 337 was required. I attempted to argue, since that particular install was most certainly NOT a major alteration. However, his interpretation was that STC paperwork itself was a Major because of the nature of the TC change. Ultimately it was less trouble to fill out the paperwork and send it in rather than argue the point...

But yes, I've also installed stuff (flap roller kits) that specifically stated in the STC paperwork that the install was a minor modification. So that's clear as mud...

So, another consideration: if you find an engine monitor kit used, you'll likely Not have the STC permission letter from the manufacturer. Installing that kit would just be a log book entry, because technically you need a permission letter to use the STC (since an STC is intellectual property). Some legacy items actually have the STC letter built into the installation instructions (legacy Garmin stuff was often like this), but it seems like this is less and less often the case.

So, still clear as mud...

 

[Bell206]

Always fun discussion...

That it is...

by an inspector before an export certificate was issued,

Key part. Some countries have export/import requirements that are above certain FAR requirements (AC 21-2). But if it wasn't that and it was a DAR doing the inspection you could have taken it to his FAA mentor. However, as you mentioned, sometimes it's unfortunately easier to bite the bullet.

since an STC is intellectual property

It depends. Unless the STC holder goes through the appropriate IP legal process (patent, etc) an STC does not protect that property. It is perfectly legal FAA-wise to copy an STC process as long as you get your own separate approvals. The only protection provided for STC data is if someone tries to install the STC on an aircraft not authorized by the STC holder. There's been several examples with the WACO case a recent one.

you'll likely Not have the STC permission letter from the manufacturer.

If you're talking pre-2000 or so then I agree as the laws werent changed until then. Before that you could copy any STC data at will.

So, still clear as mud...

Sometimes you just need to let things settle a bit and the mud sinks to the bottom.

 

[WannFly]