Is this WWI movie scene realistic? In a poignant scene of 1933 WWI film The Eagle and the Hawk (not to be confused with the same-name 1950 western film), while the pilot played by Fredric March performs a loop-the-loop in his – I believe – Airco DH.9 (is that correct?) to evade a German opponent, his observer/gunner falls out of his place and plunges to the ground (he had already been hit and probably killed by the German, but the pilot wasn't aware of it, so this is a real trauma for him).

See the scene here, starting from about 57:25.



Besides the dramatic value of this scene within the narrative, would such a fall as the gunner's be realistic? If those aircraft were capable of such manoeuvres, wouldn't the crew be somehow secured?
A loop is about 3G on the initial pull, declining to maybe half a G over the top, then increasing to 3G on the pull out.  If you go in at the proper entry speed etc and you want to make it reasonably round.  If you release enough back pressure to go even slightly negative over the top, whatever is unsecured falls out (as well as all the crap on the floor coming up into your face, and, if carbureted, the engine quitting momentarily).   All it would take is a little push on the stick while rounding the stop, for whatever reason.

Observers weren't strapped in because they had to be free to move around to do their thing. 

So that scene is perfectly plausible.