My FSO course was several years ago now, but the way I was trained is pretty simple:
- Ground/weapons safety investigators rarely extend privilege, unless they are certain the witness will not provide a statement without privilege.
- Flight safety investigators routinely extend privilege to aircrew, but they normally do no extend privilege to ground personnel unless the investigator deems it necessary.
I had heard rumblings earlier this year that the course has changed more to what disgruntledemployee mentions.