Whoever built this should be charged.
This is an uncertified experimental aircraft. At least in the US, it is up to the operator of an experimental to ensure that parts are fit for purpose.
These guys are messing with planes and don’t test enough? Is there an explanation these people aren’t just incompetent?
All materials ultimately succomb when exposed long enough at some high enough temperature.
What is the temperature range to match here?
I'm not a material scientist, but I don't believe that to be true. Metals don't to my knowledge; they suffer oxidation, which is allayed by the presence of oil.
If you mean plastics in particular, then PEEK would be ideal to my knowledge - it's suitable for immersion in gasoline and similar solvents, and I've used it in the past for a fuel pump mounting bracket that sits inside the fuel tank of a (gasoline) vehicle. I checked it after a year and it doesn't seem to be any worse for wear.
It's just a huge pain to print!
> What is the temperature range to match here?
I'm not sure, and likely couldn't be sure without a fair amount of research. If I had to print this for a plane, I'd want to do that and measure temperature in use and under high load and destructively test several drafts to ensure performance.
From what I've seen in this instance though, the failed part showed a Tg (glass transition temperature) of 55ºC - basically exactly that of PLA-CF. The pilot believed it was ABS-CF, which has a Tg of ~100ºC. If we assume that 100ºC was at least higher than the expected operating temperature, PEEK (Tg: 143ºC) would have given a ~50% safety margin.
They also handle all of the testing of parts to ensure they meet the design spec and they have the equipment to validate each printed part to ensure it doesn't have any major defects.