What happens if someone tries to open a door during a flight?

IT'S a question many of us have pondered: just what would happen if someone tried to open the exit door on a plane in mid-air? One pilot tells all.

Can a plane door be opened? Picture: Thinkstock

IT'S a question many of us have pondered: just what would happen if someone tried to open the exit door on a plane mid air?

Patrick Smith, airline pilot and author of the book Cockpit Confidential and the website askthepilot.com explains if it's possible.

'It seems that a week can't go by without hearing the latest story about a passenger who went cuckoo and tried to yank open an emergency exit, only to be tackled and restrained by those around him, who thought they were on the verge of being ejected into the troposphere (for those unfamiliar with the term, it's the lowest portion of the Earth's atmosphere).

While the news never fails to report these events, it seldom mentions the most important fact: You cannot - repeat, cannot - open the doors or emergency hatches of an aeroplane in flight. You can't open them for the simple reason that cabin pressure won't allow it.

Think of an aircraft door as a drain plug, fixed in place by the interior pressure. Almost all aircraft exits open inward. Some retract upward into the ceiling; others swing outward; but they open inward first, and not even the most musclebound human will overcome the force holding them shut.

At a typical cruising altitude, up to eight pounds (3.6 kilograms) of pressure is pushing against every square inch (6.5 square centimetres) of interior fuselage. That's nearly 500 kilograms against each square foot of door.

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Even at low altitudes, where cabin pressure levels are much less, a meagre 2 p.s.i. differential is still more than anyone can displace - even after six cups of coffee and the aggravation that comes with sitting behind a shrieking baby. The doors are further held secure by a series of electrical and/or mechanical latches.

So while I wouldn't recommend it, unless they enjoy being pummelled and placed in a chokehold by panicked passengers, a person could sit there all day tugging on a door handle to his or her heart's content. The door is not going to open (though you might get a red light flashing in the cockpit, causing me to spill my Coke Zero). You would need a hydraulic jack, and TSA doesn't allow those.

On the 19-passenger turboprop I used to fly, the main cabin door had an inflatable seal around its inner sill. During flight the seal would inflate, helping to lock in cabin pressure while blocking out the racket from the engines. Every now and then the seal would suffer a leak or puncture and begin to deflate, sometimes rapidly. The resultant loss of pressurisation was easily addressed and ultimately harmless, but the sudden noise - a great, hundred-decibel sucking sound together with the throb of two 1100 horsepower engines only a few feet away - would startle the hell out of everybody on the plane, including me.

On the ground the situation changes - as one would hope, with the possibility of an evacuation in mind. During taxi, you will get the door to open. You will also activate the door's emergency escape slide.

As an aircraft approaches the gate, you will sometimes hear the cabin crew calling out "doors to manual" or "disarm doors." This has to do with overriding the automatic deployment function of the slides.

Those slides can unfurl with enough force to kill a person, and you don't want them billowing onto the jet bridge or into a catering truck.

Click here for more information on the book Cockpit Confidential.