I believe in the German Air Force (WWI) the observer was always an officer and a/c captain. The pilot was a Sgt and looked on as some kind of chauffeur in their recce 'planes.
I have no vested interest in the pilot v others by the way....
The Dennett EngO referred to in an above post was John Dennett, he was Sengo on 3 at Gut in the late 70's. There was also a WgCdr Cheeseman at Sealand in the early 80's, an eng with pilot's wings and the CO was a Group Captain eng who's name escapes me now but he wore an AEO badge.