Which takes precedence?
In my view, a safety investigation undertaken by the AAIB should take precedence over a criminal investigation. And indeed I would argue the law reflects this. The AAIB has powers to ensure that its investigations are not obstructed and that its actions are afforded priority, for example, at the scene of an incident.
The AAIB works on very different principles to the police and CPS; it is not an enforcing authority, it has significant powers but it does not apportion blame.