Thanks for doing the math, BAe, however, an 8psi diff on the ground seems rather high. That would put the cabin altitude very far below sea level (circa -10,000 feet) even at an airport like Denver (~5,000 MSL).

On the outside of a 747 classic while talking to the engineers in the cockpit after a pressurization check we couldn't open the main entry door even when the cockpit pressure was indicating zero. The butterfly handles wouldn't budge past a certain point, eventually the upper and lower gates opened with a burst of air rushing out.

As said above the negative relief valves are probably the best bet if you don't want to damage the aircraft by punching a hole in it.

Anything other than near zero diff pressure and you better use an axe or considerably larger if you're in a rush.

Well I thought the scenario was that the system was not working correctly - after all it the system is perfectly serviceable it would have depressurized on landing.

In practice, it would be fairly difficult for the cabin altitude to be driven that low with a flight deck crew that is present and awake during ground operations, although for this thought exercise, anything is possible and theoretically you are quite right, BAe.

You could always start flushing toilets. :hmm:

Good trick if you can do it..

I refer the Gentleman to the OP - "what would be the easiest way to depressurized the aircraft from the outside?"

Good point -- I guess flushing the toilets won't work. But you could always send someone to empty them . . . https://assets.publishing.service.go...-DYS_03-15.pdf