Is it possible for an airliner to safely fly with doors open?
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a modified 747 that has an 5.5 m x 4.1 m door that is opened during flight for the installed in infrared telescope. But the door is usually closed during takeoff and landing.

But according to this story there are emergency procedures to land with an open door and it had to do so once, when it became stuck half open.



Images courtesy Wikipedia