Just out of interest and at the risk of thread drift (and this thread has wandered a bit already!) mention of DC9 elevators reminded me of something I've never cleared up.
From the 1960s to the 1990s I regularly saw DC9s in service around Europe and the USA. Often when parked at a gate one elevator would be up, the other down as if they were decoupled. Don't recall seeing this on any other type, T tail or not.
Anyone know the reason, if this was just a DC9 phenomenon and why?