Why an airliner’s door won’t open in flight

Alaska Airlines passenger Alexander Michael Herrera attempted to open the plane’s emergency exit door midflight between Anchorage, Alaska, and Portland, Ore., on Monday. There was no danger to passengers, as the emergency exit door was locked during flight. Who unlocks a plane’s emergency exit in the event of an actual emergency?

A computer does it. Most of the jets in the Alaska Airlines fleet are Boeing 737NGs. The over-wing exit doors in these planes are equipped with electronic locks that engage only when the plane is in flight. If the plane slows to a near stop or loses altitude, the door will unlock. Also, since the locks require electricity to hold the door closed, a loss of aircraft power will return them to the unlocked position. Flight attendants sometimes complain about the locks’ tendency to disarm based on any minor malfunction, because, if a warning light indicates a lock failure, an attendant has to guard the door. The good news is that a malfunctioning emergency door lock has never prevented escape in a true emergency.

Older Boeing 727 planes, most of which have gone out of commercial service, have a lower-tech lock with a colorful history on the rear stairway. On the day before Thanksgiving 1971, a man using the pseudonym Dan Cooper hijacked a plane, ransomed the passengers in Seattle for $200,000, and ordered the pilot to fly him to Mexico City. As the plane flew over Oregon, however, “Cooper” released the plane’s aft stairs and parachuted out of the aircraft. No one has heard from the hijacker since, but his crime led to a series of copycats over the next year. The strategy became so popular that it got its own name: para-jacking. In response, Boeing equipped the aft stairs on 727 planes with a spring-loaded lock on the outside of the craft. When the plane gains speed, the air movement forces a latch beneath the stair door, preventing the stairs from popping open. This so-called Cooper vane mechanism carries the name of the hijacker who inspired it.

On some aircraft, all of the emergency exit doors open inward. Pulling open an inward-swinging emergency exit door in a pressurized plane at cruising altitude would be beyond the strength of an ordinary airline passenger, which makes locks unnecessary. Depending on the surface area of the door, opening it at 35,000 feet would be about as difficult as lifting a subcompact car off the ground. The door can be opened only once the plane descends or depressurizes. Some planes built in the past 15 years, in contrast, feature the outward-swinging doors. While the new style requires locks, it solves the safety hazard of requiring someone to maneuver an unwieldy slab among frantic passengers who are bottlenecking toward the passage. Unruly passengers attempt, and fail, to open emergency exit doors midflight with some regularity. In 2011, it happened twice on Delta airlines alone. In May of that year an apparently intoxicated passenger attempted to escape a Boston-bound flight at cruising altitude, and another passenger tried to open a door between Las Vegas and Atlanta in October.

Opening a plane’s emergency exit door while the aircraft is on the tarmac is considerably easier. Last year, a passenger on Vietnamese Airlines sprang the emergency door for his seatmate, who wanted off the plane to calm her crying baby. In 2007, an Air Deccan passenger opened an emergency door because he was annoyed about his flight being diverted. There was also the highly publicized 2010 case of the fed-up Jet Blue flight attendant who cursed out a passenger on the intercom and left the plane via an emergency slide. Such behavior typically carries fines, but refitting the slide or repairing damaged doors usually costs tens of thousands of dollars — far more than most fines.