Is it impossible to open the door on a jet?

[ICEMANSAV]

Is it impossible to open the doors in flight? Someone told me it was in fact impossible but obviously the action is acted upon so strongly due to upsetting other passengers. So my question is " if someone does this are they actually endangering peoples lives?"

[Clanad]

Since these types of aircraft are pressurized, you would think that it would be a simple matter to open the doors/emergency exits since they have outward pressure.  But, next time you are on such an aircraft, take a look at the instructions posted on placards next to the emergency exits.  Notice, you have to pull the handle, pull the door/window inward, turn it on its side and throw it out.  The reason is simple, the door/window is a plug type... that is it will only fit in its receptacle from the inside.  Clever, no?  This assures the doors and windows cannot be removed when the aircraft is pressurized.  Additionally, most of the locking mechanisms on newer aircraft are energized electrically when the aircraft wheels are not on the ground (called WOW, i.e., weight on wheels switch mounted on the wheel assemblie(s).  I did have a case once, on a Boeing 727, where the Auxilary Power Unit (APU) which supplies heat and electricity to the aircraft on the ground (a small jet engine) and whose exhaust vent is in the right wing root, "torched".  It flared slightly, which is not uncommon.  An over excited passenger thought the aircraft was on fire and opened one of the overwing emergency exits and tried to get out of the aircraft while we were taxiing.  The flight attendants restrained him, notified us and we returned to the gate since it takes a maintenance action to re-fit the exit...

[ICEMANSAV]

Thanks for the detailed response Clanad!