A man opened the exit door to an airplane during a flight in South Korea. The flight was in the process of ending so the aircraft was not that far from the ground. It was about 700 feet in the air. When the plane is much higher, at a cruising altitude of about 30,000 feet, the emergency exit door cannot open due to cabin air pressure keeping it shut. However, when the plane is lower to the ground, cabin air pressure is gone. The door can be opened close to the landing so it can be opened in the event of an emergency when the plane needs to be evacuated on the ground. Nobody was hurt as a result of the action. However, some people reported difficulties breathing.
SOURCES:
Asiana Airlines: Passenger arrested for opening plane door during South Korea flight – BBC News
See the moments after a passenger opened a plane door during flight – ABC News
Passenger opens plane door during flight in South Korea
Nightly News Full Broadcast – May 26 – YouTube