A bit more on the use of the word "crew" Skycop mentions that the observers don't play much part in the pure aviation side of the work, well, that may be the case (although in my experience they give good lookout, at the very least).. but take the cases of a Nimrod or AS Seaking - filled with people doing a task that has nothing to do with flying the aircraft but I'd hesitate to call them passengers, in their hearing anyway.
Good point about the standardisation, though, each force seems to want to re-invent the wheel when it comes to setting up an ASU.