In article ,
wrote:
Taxiing in on a just landed United flight at LHR a few weeks
ago, I caught a quick glimpse through a window across the
cabin of what looked (to a non-expert) like a semi-derelict
small-sized "Super Guppy" parked off by a big hangar:
fat fuselage, three engines (one huge one up in the tail),
faded bile-green color, what looked like big rust streaks
running around the fuselage.

What might I have been seeing?

Fire trainer?

Andy