The door came loose but didn't come off, it just went far enough back to go into the tail rotor
It wasn't a door, but an part of an engine cowling which came off. The reason for it coming loose was never established.
Here's two more. A UEO who had no more idea about running an Air Support than my Aunt Bessie.
A DUEO who stated publicly that he'd only send Observers on (free) Flight Safety Courses when it became compulsory.