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Today it has been reported that a passenger managed to open the emergency exit door of an A321 in-flight. According to the report the aircraft (performing flight OZ-8124 from Jeju to Daegu in South Korea) was descending towards Daegu when a left hand emergency exit opened, causing injuries to 9 passengers. The police arrested a man who was sitting next to the emergency exit and said he had been touching the lever.

I was under the impression that these exits were plug type doors, and so they are firmly pressed into their frame by the pressure difference between the cabin and the outside. Furthermore, I assumed some kind of lock (pressure lock, or something electromechanical) would prevent operating the door handle in-flight.

How is it possible that a such a door opens in flight?

Note: I am seeking to understand the mechanics of the emergency exit doors of the A321, not looking for speculations about what may have happened in this specific case.

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    $\begingroup$ Maybe the aircraft was already under the height at which the pressure equalizes between inside and outside? This height is 8000ft. $\endgroup$
    – U_flow
    May 26, 2023 at 9:42
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    $\begingroup$ @U_flow cabin pressure is gradually increased during descent, so the cabin altitude also lowers below the ~8000ft that you have during cruise. $\endgroup$
    – Bianfable
    May 26, 2023 at 10:04
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    $\begingroup$ @U_flow, Bianfable is right; check out the chart in this answer. $\endgroup$ May 26, 2023 at 11:15
  • $\begingroup$ Huh, good that I did not formulate this as an answer :) $\endgroup$
    – U_flow
    May 26, 2023 at 11:45
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    $\begingroup$ @Mazura that would severely compromise the "emergency" nature of the door operation $\endgroup$
    – Doryx
    May 26, 2023 at 22:54

3 Answers 3

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According to the FlightGlobal article you linked, the L3 door was opened (the emergency door behind the wing on the left side). All 8 doors on the A321ceo are plug type doors that cannot be opened when the cabin is pressurized. (Note that the A321neo has a cabin flex option for different door layouts)

I only have access to an A320 FCOM:

The aircraft has four plug-type doors that open outward and forward. There are two of these on each side of the fuselage (two forward, two aft). They can be operated from inside or outside the aircraft. Normal operation is manual, with hydraulic damping.

Each door has features that tailor it to emergency situations:

  • An escape slide stowed in a container attached to the inboard lower side of the door
  • A damper actuator that limits door travel in normal mode, but in an emergency acts as an actuator for automatic door opening
  • A slide arming lever.

(Airbus A320 FCOM - Doors - Description - Passenger Doors, emphasis mine)

The following YouTube videos show old Airbus training videos for the A321 and essentially say that the Type C emergency doors (L2/3 and R2/3) are identical to the main doors, except for size (only L2 is larger) and emergency escape slides:

The aircraft must therefore have been depressurized at the time of the incident. During descent, the cabin pressure targets destination pressure +0.1 PSI:

During descent, the controller maintains a cabin rate of descent, such that the cabin pressure is equal to the landing field pressure +0.1 PSI, shortly before landing. The maximum descent rate is 750 ft/min.

(Airbus A320 FCOM - Air Conditioning and Pressurization - Pressurization - System Operation)

Shortly before landing, the cabin pressure is therefore only slightly higher than the outside. According to the FlightGlobal article, the door was supposedly opened at 800 ft. Together with the pressure from the nitrogen bottle that assists the opening if the door is armed, this should make it possible to open the door.

Note that there are no centrally controlled locks on the doors. The door locking is entirely mechanical and controlled by the door handle. Instead of pressure locks, there is a Cabin Pressure warning light that warns the crew on the ground in case of residual pressure difference:

Red Light: flashes when one or both engines stopped, the slides are disarmed, and the cabin differential pressure is above 2.5 Hpa.

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    $\begingroup$ The fact that there is a warning light above 2.5 hPa (0.0025 bar, 0.04 psi) suggests that there is a range of pressures where the door can be opened and it violently slams open. But I could not find any number of the maximum pressure difference at which this can happen. $\endgroup$
    – jpa
    May 26, 2023 at 17:12
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    $\begingroup$ rough back of envelope numbers: 0.1 PSI * ~1m^2 of door surface area -> ~150 lbs of force to open the door. Seems possible with some mechanical advantage and the nitrogen assist you mention. $\endgroup$
    – mbrig
    May 26, 2023 at 21:17
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    $\begingroup$ I remember back in the day when I worked part-time as a baggage handler, we sometimes had to open the rear door (mostly of Boeing aircraft) [we were sometimes rostered on to the cleaning crew if they were short]. We were always trained never to open the door until we received a signal from the cabin crew that the door was safe - we we told it would otherwise automatically blow open. I assume this was the nitrogen as there was no pressure difference (the front door was usually already open) $\endgroup$ May 28, 2023 at 22:16
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CNN reported that the passenger "opened the door when the aircraft was about 700 feet (213 meters) above the ground and about two to three minutes from landing in the city 150 miles (240 kilometers) south of Seoul."

At 700 feet, there is not enough pressure-differential between the inside and outside of the plane to make opening a door difficult.

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    $\begingroup$ As I learned in this question: There is always a little pressure difference in flight. See the discussion and link under the question. $\endgroup$
    – U_flow
    May 26, 2023 at 13:30
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    $\begingroup$ @U_flow Yes, a little, but at 700-800 feet it is just that - little. From sea level to 700 feet is only about 0.3 psi, for example. For a Type C door, that would require about 400 pounds of force to open. Still not a feather, but possible (especially given the lever arm involved.) Whereas in cruise it's more like 10 psi differential, requiring over 14,000 pounds of force. $\endgroup$
    – reirab
    May 26, 2023 at 17:48
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According to this video,

, the aircraft was on final approach & was at about 600ft.The door was armed & therefore its opening was assisted by a compressed nitrogen device. The nature of this door is that although it opens forward, it does so remaining parallel to the fuselage, a bit like a common delivery van side door. The event was "interpreted" by the aircraft system as a valid emergency exit & the escape slide was also deployed. The slide was ripped off by the slipstream. I have no idea if this door should normally be inoperative without weight on the undercarriage, although I could imagine that it is thought that the aircraft might not necessarily be rightside-up, or even have its undercarriage extended, when emergency exit is required.

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    $\begingroup$ Good to see that Juan Browne 'Blancolirio' has at least one aviation.stackexchange.com tab open in his video. Wouldn't be surprised if his research took him to this question :-), he is using the video linked from Bianfable's answer to explain how the doors work. $\endgroup$
    – DeltaLima
    May 28, 2023 at 19:59

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