Please be aware that this @ notation sends an email to the person. Most of the time this is not needed. It causes people to turn them off and then you can’t contact them because they don’t receive PMs.
Peter wrote:
EASA doesn’t like FAA-PMA and has no equivalent regime, and has threatened to block FAA-PMA, but if people could not use FAA-PMA, EASA-reg would grind to a halt.
I don’t know where you get your information from but the above is incorrect. EASA have accepted PMA parts since at least 2007.
The UK CAA specifically also accept PMA parts under the CAA-FAA Bi-lateral:
UK_IPA_FAA_pdf
7.6 Additional Documentation Requirements for FAA PMA Parts
For a PMA part that will be installed on a product which has been certified or validated by the CAA, one of the following statements should be written in the remarks block of the FAA Form 8130-3, as applicable:
7.6.1 For a PMA part which is not a “critical component” (see definition paragraph 1.12.18), the following statement should be written in the remarks block of the FAA Form 8130 3: “This PMA part is not a critical component.”
7.6.2 For a PMA part conforming to design data obtained under a licensing agreement from the TC or STC holder according to 14 CFR part 21 (see paragraph 3.3.4), the following statement should be written in the remarks block of the FAA Form 8130 3: “Produced under licensing agreement from the holder of [INSERT TC or STC NUMBER].”
7.6.3 If the PMA holder is also the holder of the CAA STC design approval which incorporates the PMA part into an CAA certified or validated product (see paragraph 3.4), the following statement should be written in the remarks block of the FAA Form 8130 3: “Produced by the holder of the CAA STC number [INSERT THE FULL REFERENCE OF THE CAA STC INCORPORATING THE PMA].
one of the following statements should be written in the remarks block of the FAA Form 8130-3, as applicable
And you prove me right 
You are generally not gonna get an 8130-3 form from a typical US company, thus annotated. And if it came via a reseller, say A/Spruce or actually any US seller, the chances will be zero.
Like so many of these discussions, the EASA “concession” turns out tp be worthless.
Yes you can use FAA-PMA on EASA-reg planes but that’s because the maintenance business looks the other way. The alternative is to ground most of the GA fleet.
The old “critical part” thing 
Peter wrote:
You are generally not gonna get an 8130-3 form from a typical US company, thus annotated. And if it came via a reseller, say A/Spruce or actually any US seller, the chances will be zero.
Really? See Box 12
Garmin, of course, do it because Garmin sells to Garmin and then Garmin sells to Garmin dealers.
Now try this for the PMA parts which make up a chunk of an IO540 engine, for example.
Peter wrote:
The old “critical part” thing
This is clearly defined in the FAA/EASA Bi-lateral:
1.12.18 “Critical Component” means a part identified as critical by the design approval holder (DAH) during the product certification process or otherwise by the Authority for the State of Design (SoD). Typically, such components include parts for which a replacement time, inspection interval, or related procedure is
specified in the Airworthiness Limitations section or certification maintenance requirements of the manufacturer’s maintenance manual or ICA
So typically this would be something with a fatigue life on a structural component, or an engine cycles limit such as with a turbine blade.
Peter wrote:
Garmin, of course, do it because Garmin sells to Garmin and then Garmin sells to Garmin dealers.
What’s wrong with a US company following the rules properly?
At this point I give up. You have the evidence that parts ARE produced under PMA for other than direct replacements.
Fair enough – we had wires thoroughly crossed. I was hoping my 1st post was clear but it wasn’t.
You showed that there is a special scenario where PMA can be used for avionics; typically within an in-house certification pipeline all within one company (Garmin).
Peter wrote:
You showed that there is a special scenario where PMA can be used for avionics; typically within an in-house certification pipeline all within one company (Garmin).
Garmin, Dynon, UAvionix, Flight Display Systems, Electronics International etc. It’s not an unusual or special process.
What would stop someone making a plug compatible KC225 autopilot computer, and the KS27xC servos for it, under PMA?
Peter wrote:
What would stop someone making a plug compatible KC225 autopilot computer, and the KS27xC servos for it, under PMA?
Nothing apart from cost. Avidyne did it to replace the S-Tec 55/55X computer although they kept the original servos. You’d have to do an STC and do all of the required flight testing and use a DER to coordinate the whole process.
As part of gaining the PMA, you’d have to satisfy the FAA that you have a suitable manufacturing capability with an appropriate QA system.
