Originally Posted by
FE Hoppy 
Anyone want to list aircraft with manual dump valves?
The Vanguard (VC9 - AKA Whispering Warehouse) had a manual "unpressurised flight valve" on the co-pilot's side.
But they all depend on someone alert enough to operate them.
The Saudi Arabian TriStar only needed the Flight Engineer to put the pressurisation controller back to "Normal" and the squat switch logic would have opened both outflow valves fully. The system was left in the "Standby mode" and so the outflow valve positions were determined by the Flight Engineer. (The Fwd was found Fully closed, the Aft almost fully closed).
See
http://www.aviation-accidents.net/re...load.php?id=43 page 81.
Once all electrical power was lost, the valves are held in their position by brakes.