So, doing a major alteration is not much different than doing minor. Am I getting this right?
If you have an STC, and it covers everything you want done, then the paperwork side is trivial, yes 
You get another discussion if you need to deviate from the STC. Is it a Major or a Minor? It depends… if it is something little, most people “just do it” especially if it is covered by the generic repair manual a AC43-13-2… 
Is there a chance I could find actual IA on this forum who’d be willing to travel to Slovenia for this (some time this year)?
Probably a good chance, although who knows when restrictions will finish? The UK has just started a 14 day quarantine on anybody returning.
Is there a chance I could find actual IA on this forum who’d be willing to travel to Slovenia for this (some time this year)?
You could ask Justus of ACG He’s the A&P/IA we work with on our Mooney and I can recommend him. I know that he‘s willing to travel but I‘m not sure if he’ll work on turboprops. But anyway, asking won’t cost you a thing.
Block 8 of the 337 requires the use of FAA approved data to justify the validity of the modification. An STC includes FAA approved data for the modification. A field approval requires that the data be submitted to the FAA for the proposed modification and reviewed by the FAA and their signature in block 3 before the modification can be approved. A DER can also generate FAA approved data within the limits of their authority
Just had a conversation with FAA A&P IA directly. Got confirmation that Form 337 and the sign-off are the only things needed in case STC is used and fully followed (which is the case for most of us). Otherwise, almost the same, but with DER (to make sure it passes). The only thing that eats me from inside having to throw away a professional (and very practical!) Honeywell GNS-XLS with all the necessary capabilities for a Garmin touch toy. World is going a direction which I really don’t get… ;-)
