Do we know whether the part was made out of spec, or whether the spec specified inappropriate materials?
According to https://assets.publishing.service.gov.uk/media/69297a4e345e3...
> The aircraft owner [...] understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature of 105°C [...] he was satisfied the component was fit for use in this application when it was installed.
> [...] Two samples from the air induction elbow were subjected to testing, [...] The measured glass transition temperature for the first sample was 52.8°C, and 54.0°C for the second sample.
I've known 3D printing folks who run off a throwaway prototype in a cheap, easy-to-print material to check for fit before printing in more difficult, expensive materials. Easy to imagine a careless manufacturer getting the PLA prototype mixed in with the ABS production parts, and selling it by mistake.
Of course, the aviation industry usually steers clear of careless manufactures....
I've used PA6-CF for similar purposes in the past. Obviously not for aircraft, though.
If you want to slap 15 weed-wacker engines to a wing you made from styrofoam and call it an airplane, the FAA will not stop you.
I'm oversimplifying, a bit, but less than non-pilots might think.
In other words, the engine maker probably has some thoughts about how that piece should be made, but the FAA would have no problem with you installing it on an experimental.
A better choice would have been PEEK. But even then, I would have done a lot of on-the-ground testing before trusting my life to a part from the printer.
And PA-CF is usually pretty good with temps, I have used it for parts on engines before with good results, but not in safety critical scenarios.