A passenger on an Asiana Airlines flight in South Korea managed to open an exit door a few minutes before the plane landed:
The obvious question: how was this possible? Previous discussions have indicated that when at cruise altitude, cabin pressure holds the door shut tightly against the fuselage, making it physically impossible for a passenger. But this plane was reportedly at ~700 feet on final approach when it happened, so there was no appreciable cabin pressure. But shouldn’t there have been some kind of interlock(s) to prevent the door from being opened by anyone until the plane was on the ground? Landing gear loading? Airspeed? Child lockout button in the cockpit?
I am no pilot, and we do have Doper pilots here, but I’m going to guess that at that low altitude, the only thing keeping the door shut was the usual turn-bar handle that opens the door. The pilot had probably also instructed the flight attendants to “prep the doors” before this incident, in preparation for landing, which would have meant the doors being in a position where turning the handle was all that was needed to open it, in case there was a crash or some emergency after landing.
No, there shouldn’t be. Imagine if there were, but it failed to unlock in an actual emergency and everyone died inside the plane because they couldn’t evacuate.
The pressure difference at altitude and the presence of flight attendants seems to be doing fine.
It looks to me in the video that there’s some sort of mechanical or hydraulic assist once someone pulls the open handle, which was apparently enough to open the door against the airstream, I guess? Or maybe the door only did the first part of the opening: sliding open partway.
Things like this can be designed to fail safe. The interlocks could require electrical power to remain locked, so a loss of power would enable the doors to be opened. Also, it could be designed so that a “safe” condition indicated by any single interlock - gear loading, low airspeed, low radar altimeter reading, cockpit switch, etc. - could enable the doors to be opened. Of those, only the last one would require deliberate human action; each of the rest would happen automatically a few moments before or after touchdown.
While I don’t have any serious doubts about the ability to design a good failsafe interlock system that prevents anyone from opening the door until the plane is actually on the ground, I understand that what happened on the Asiana flight is an extremely rare occurrence, and the expense of adding an interlock systems to the entire passenger airliner fleet is probably not justified in terms of lives saved. Case in point, nobody actually died this time.
Since the air outside of the aircraft was moving faster than the air inside the aircraft, could the Bernoulli effect have come into play? Obviously, a door isn’t going to swing wide into the airstream; but would Bernoulli allow for a pressure differential enough to allow the door to come ajar?
The article includes video captured by a passenger before the plane landed. Judging from the amount of daylight streaming in, it appears the door was wide open while still in the air, meaning the door had swung completely out and far forward into the slipstream. It’s plausible that Bernoulli could have created enough pressure differential to open the door outward a few inches, but it doesn’t seem plausible that it could swing the door forward several feet outside the fuselage like that.
It also looks like the emergency slide got deployed in mid-flight and ripped off by the slipstream. Are there maybe some hydraulics that make the door open all the way when the emergency slide is armed?
The doors on an Airbus do not swing out on ordinary hinges like the door to a house. The door pushes more or less straight outwards parallel to the fuselage, then translates forwards edge-on to the airstream. So it’s never a barn door sideways to the wind.
There are some real questions about how the forces added up to enable to door to move upstream into the latched open position in flight. IANA Airbus pilot but conventional wisdom is that unlatching the door in flight is readily possible, and especially at low altitude with negligible pressurization. But also that pushing it upstream against the airflow would be impossibly difficult. Clearly conventional wisdom is lacking a bit.
No, but on a A-320 family there is a pneumatic ( nitrogen ) charge that acts on an actuator that opens the door if the escape slide is armed.
I’d still like to know how the door was able to open if the aircraft is pressurized. That’s a lot of surface area and even a small cabin differential will exert a ton of force on the door ( perhaps literally ) against the stops.
At 700 feet altitude I don’t think the plane is pressurized. The atmospheric air pressure at 700 feet is about 14.4 psi, compared to 14.7 psi at sea level. Planes at cruising altitude are pressurized to about 11-12 psi.
Even so, the door has a substantial thickness - maybe 6 inches? call it five feet (60") tall, and you’ve got 360 square inches of forward-facing projected area that gets hit with ram air pressure from the slipstream. According to this chart:
170 MPH gets you about 0.5 psi of ram pressure. Times 360 in^2 = 180 pounds of force resisting whatever effort is trying to move it forward into the slip stream. The crazed passenger who opened the door certainly couldn’t put out that kind of force in that configuration. It would require the N2 charge that @BrickBat mentioned in order to make that happen.
Agree that it was the assist charge that enabled the forward motion. For exactly the reasons you describe. I was mostly clarifying that folks who’re thinking the door swung open like an ordinary room door don’t have the correct picture.
And color me somebody who is surprised to door assist charge is enough to overcome that much air resistance. But it did.
It’s easy to start mixing units. Which can lead to confusion. Not that you are confused, but some readers might be.
What matters to doors opening or not is the differential pressure, not the absolute. At high altitude cruise, a typical differential pressure is about 8psi, while the outside absolute pressure is around 4psi, so yes, as you say, about 12 psi absolute in the cabin. Which in turn corresponds very roughly to a cabin altitude equivalent of 8,000 feet above sea level.
At takeoff and landing you want the cabin very slightly pressurized. On the order of 0.25psi differential. So typically during descent and approach the cabin control system will drive the cabin altitude down (and hence absolute pressure up) to slightly below airfield elevation so the internal pressure is that small amount higher than the external pressure at ground level. And upon touchdown the remaining differential pressure is vented during the slowdown, such that by the time you’re ready to leave the runway the differential pressure is zero.
Part of the mechanical opening sequence of many doors is that a small port opens which will vent a tiny differential easily. But would not be enough to dump a whole cabin in anything near real time.
At a mere 700’ above the ground the differential pressure will be small as you say. Enough to allow the small vent to drop the rest of it reasonably quickly and then the person leaning on the handle has a chance to unseat the door against the latches and now we’re off to the races.
Why is that small differential desirable? Does it help with structural stability, in the same way that a sealed/pressurized soda can is much harder to crush than an opened one?
I think @LSLGuy has covered the technical side. I will just note that “Aviation Expert” Geoffrey Thomas is an Australian who is not held in very high regard by aviation professionals. He’s a general aviation guy who tends to provide commentary beyond his area of knowledge.
It helps the door seat snugly against the fuselage. Otherwise they rattle rather disconcertingly as we’re pounding down the runway.
The other thing is that ears are sensitive not only to the rate of change in pressure (more is worse), but also the acceleration (rate of rate of change of pressure). Both taking off and landing are rather abrupt changes in aircraft vertical velocity and hence altitude = outside pressure. By stabilizing the cabin slightly pressurized, you don’t get a perceived pressure bump as the airplane leaps into the air or crunches onto the ground.
The pressure is kept low enough that it’s not an impediment to getting doors open in an emergency.
Wow. I have no direct personal hands-on experience with Airbus doors. But an awful lot has to go wrong with the closing of a Boeing door before it could open inadvertently.
