Originally Posted by
xyzzy
I was recently on a Rossyia TU-134 that had an amazing amount of fog/mist shooting out of the AC vents due to humidity differences inside/outside.
A real classic aircraft for this is the British Aerospace 146, with the vents above the windows "steaming". I asked a couple of aircraft engineers why and was given quite contradictory answers, so I guess it's not a precise science.