People died so it was inevitable that he would be.
I don't think that is a given.
They are specifically trying to bypass AAIB protections before the report is completed.
It's hard to believe this won't affect the investigation, which should not be about whether or not he is culpable but how it was allowed to happen and how to stop it happening again.
Edit: Sorry, I have just reread and realised you mean it is a given that he would be questioned. I do agree with that.