If a passenger were to open an exit door during flight, the plane would likely encounter turbulence that could be hazardous to the structural integrity of the aircraft and the wellbeing of those on board. Depending on the altitude and speed of the plane, the plane would most likely descend quickly and the pilots would need to take emergency measures to land the plane safely. Pilots may need to deploy the parachutes on the plane to slow the descent, or they could choose to reduce speed and altitude manually, as well as activating emergency landing procedures.