Google: EASA FAA (EU USA) BASA. Then read the technical implementing procedures (TIP). The same also exists for TCCA – EASA (CAN – EU).
EASA accepts alterations on non-critical components that are substantiated via Form 337, as detailed in the EASA-FAA Technical Implementation Procedure (TIP) rev 5, paragraph 3.2.8.2 EASA Acceptance of FAA Alteration Data:
“Except for alterations on critical components, FAA-approved or accepted alterations per 14 CFR Part 43 installed on a used aircraft exported from the U.S., regardless of the State of Design of the aircraft, are considered approved by EASA at the time of import to the European Union. EASA shall accept such FAA alteration data when substantiated via an appropriately executed FAA Form 8110-3, FAA Form 8100-9, FAA Form 337 or logbook entry.
Alterations on critical components must be EASA-approved via STC, in accordance with TIP paragraph 2.2 (Design Approval Procedures for Supplemental Type Certificates (STCs)).
An FAA STC whose installation is documented on a Form 337 must be approved by EASA in accordance with TIP paragraph 2.2.”
OK; that bit is exactly what I have been saying. They accept Major Alterations (= form 337) which (obviously) have been properly documented, and with some conditions. Minor Alterations are not accepted and that is fairly likely to catch you out when you import something.
Another thing to watch out for is a misinterpretation of an STC. This can happen on an EASA-EASA transfer too; one case I know of, where a major avionics job was done on a type which wasn’t (quite) on an STC, probably demolished the value of the plane. The original installer – a well known “reputable” company – offered to continue doing the Annuals on the plane for ever, if nothing is said 
EASA shall accept such FAA alteration data when substantiated via an appropriately executed FAA Form 8110-3, FAA Form 8100-9, FAA Form 337 or logbook entry.
Logbook entry = minor alteration.
That’s well spotted. However, the whole paragraph is this
and to me it reads that even a logbook entry needs to be “FAA approved or accepted”.
In any case, the accepting authority gets plenty of wiggle room there
The Export CofA may cover this, however. Doesn’t it certify the whole aircraft as “accepted” by the exporting authority? I don’t think so, recalling my experience of G to N in 2005. Some stuff done by Air Touring was not accepted by the FAA inspector (who was supervising the DAR) and new paperwork had to be generated. OTOH I didn’t have an export CofA; I used a concession mentioned here.
The FAA gives explicit approval for all major mods, and implicit approval for minor mods where the approval authority is delegated to the A&P. As such the A&P logbook entry reflects “FAA Approval” since the entries that can be made are regulated.
cf. 43-210A:
“3.2.2.1 Minor Repair or Minor Alteration. If you are properly authorized, you may
perform a minor repair/alteration using acceptable data, and without approved
data. You may document the alteration or repair in the product’s logbook per
§ 43.9 indicating return-to-service.”
I’m late to this but you guys got the idea right: the key is that even though FAA mods (major or minor) cannot be validated upon import into the EU, they can be approved for the specific aircraft serial number. In practice very few mods are not approvable via that route in the piston world. Turbines are different since they do have critical airworthiness items (mostly engine life-limited parts) whose changes cannot be imported unless fully validated.
Rather than debate amongst us or with the authority, the best is to keep your CAMO onboard and deal with a CAMO that has done it before. If your CAMO has doubts about a specific mod, then don’t go that route. If your CAMO is confident, then once they issue their ARC recommendation and you have an export CofA, you are 90% of the way towards your EASA CofA. Still, EASA ruling entitles individual NAA’s to follow specific import inspection procedures. Some are mostly a paper exercise, some insist on a test flight and a physical inspection. Again I suggest to go with a NAA/CAMO combination that has worked successfully before, and they will provide all required serial-number-specific guidance on the path to EASA airworthiness.
A couple of further potentially important details:AD’s: most large types have incompatible FAA/EASA AD’s : ie FAA AD’s which, when implemented, impede an EASA AD or vice-versa. Although rarer in the small aircraft world, make sure you check all AD’s for compatibility (ie, that all applicable and due EASA AD’s are complied with at the time of import or you have identified a compliance path)
Export CofA: make sure the issue date is reasonably recent (I dont recall that there is a hard deadline): ie make sure the issuance is delayed until shortly before the import, so you don’t end up submitting to the NAA in your application package a six-months old export CofA whose validity they may question
Last, some sound advice given previously: why bother with the change and not keep it on N-reg? Especially if it is a rare type or one with a rare mod, maintainability will be much more straightforward in FAA-land. The paper exercise is comparatively larger for a low-value aircraft and hence the justification for the reg change is more difficult.
Oh, and I am not sure it was mentioned before: make sure the type does have an EASA type certificate or else you will not be able to import it.
the key is that even though FAA mods (major or minor) cannot be validated upon import into the EU, they can be approved for the specific aircraft serial number
I thought I had seen that somewhere before
Very interesting.
Peter, did you notice I marked “logbook entry” in bold?
The whole point about modifications via logbook entry in the US is that the FAA is not involved. An IA can do it.
Responsibility for determining whether an alteration is major or minor lies with the mechanic who performs the alteration. A mechanic who asks the FSDO is simply passing the buck, not doing his job—and not doing you any favors.
If the mechanic determines the alteration is minor, he can perform it using methods, techniques, and practices he considers acceptable, and then sign off the work with a simple logbook entry. The FAA never gets into the act (and doesn’t want to)
Source: https://www.aopa.org/news-and-media/all-news/2017/april/pilot/savvy-keep-it-minor
