Asiana Airlines: Inside cabin as plane door opened mid-flight
Reportedly a passenger opened the door of an Airbus A321 shortly before landing. In my ATPL theory course, we calculated the force required to open an airliner door on the ground with the aircraft pressurisation system operational, although with a very small pressure differential. The conclusion was that the force required was beyond what even a seasoned weight-lifter could muster. I’ll try and recall the assumptions and recalculate later, but a bit confused as to how this incident happened. Could the pressurisation have been turned off?
I don’t have the flights detail… but close to the ground the DP can be low, and is then gradually reduced as in this schematic. Using the emergency open door assist would probably have made this possible.
Also this very act could have been helped by some defect in the pressurisation system itself, or manual settings as performed by the flight crew, a challenging situation in itself.
That is a helpful diagram. If I understood it correctly, the likely minimum pressure differential is about +0.1 psi. From memory, this is smaller than the figure we used for the rough calculation in the theory class. 0.1 psi = ~690 Pascals. For a door area of 1 m^2, that is equivalent to lifting 69 kg, which is probably a bit much for the average passenger sitting down and operating the door at an angle, but if there is a built in assist, then it becomes plausible.
The diagram above doesn’t show any period of a negative pressure differential, but is it possible at some point during a quick descent? Especially if a high cabin altitude was being used in the cruise.
derek wrote:
is it possible at some point
Theoretically, everything is possible 
But not supposed to happen. From the moment the pre-pressurisation phase starts, until the de-pressurisation phase occurs, the cabin should be positive., i.e. pressurised to a certain point.
In addition to the 2 situations, tech defect, rather improbable as 2 press controllers are installed, and manual control by the the flight crew, a possibility of setting a wrong landing elevation prior to the flight could lead to a negative cabin P.
Back to this very case, and looking at the video we don’t know at exactly which point said door was open… but as you demonstrate, it must have been at a very low altitude. And the pax was probably not sitting when he/she operated the lever, but rather standing and used both hands to lift that lever and therefore provide a breath of fresh air to his fellow passengers.
On another interesting tech note, I noticed that the emergency open door assist was strong enough to swing the door open against the slipstream… I remember its action being quite strong from recurrent training, but would not have thought it’d be that strong… also looks like the door is slightly ajar, maybe a damaged hinge.
News reports claim the aircraft was at 700ft when the door was opened.
And here’s a pretty good case presentation
Thanks for posting it. He used the same +0.1 psi figure, and a little bit bigger door size to come up with a force equivalent to lifting ~95 kg. That still sounds like a fair bit to me, but perhaps the door handle provides leverage, and the door assist appears to kick in after just a little bit of movement.
The door handle has quite a bit of leverage.
In fact the first movement of this door for opening is “mostly” up on rollers along the slotted locks/guide fittings, thereby lifting the door’s full weight without assist.
I say “mostly” because the slots are sloped in such a way that the door must also move somewhat inwards. The open handle leverage is designed so that the door can be lifted+opened with reasonable force even if the aircraft remains accidentally pressurized with the ref’d residual 0.1psi after landing, hence avoiding a potential delay in an emergency evacuation.
On a sidenote, even if the pressurization controllers fail or the pilots set them manually wrong, all aircraft are designed so that negative delta P is not possible unless the ditching switch is activated.
After lifting about one inch, the rollers are free from their slots and the door is able to hinge out and forwards, which is the part of the door opening movement that the pneumatic assist is for.
These guide fittings can be seen at different locations around the door frame while boarding the aircraft:
all aircraft are designed so that negative delta P is not possible unless the ditching switch is activated.
That’s really interesting. I read somewhere the cabin pressure is dumped if weight on wheels is detected.
