Passing through the door on an aircraft can represent the start of an exciting journey onboard, usually kicking off with a warm welcome from the cabin crew. For others, it signifies the optimism of beginning a new trip, the anxiety of starting a new life, or the excitement of returning home after a long period.
While some might only know about passenger doors, an aircraft has several other doors, including the cockpit, cargo compartment, and avionics compartment doors. However, in this article, we will focus on the most common ones. To avoid rapid depressurization, it is paramount that passenger doors cannot be breached inflight, so let’s examine how they work.
Keeping doors in place
Aircraft doors are held in place physically by a series of electrical and mechanical latches. This is one way in which they are kept secure despite the strong forces that aircraft encounter in flight. This also minimizes the risk of accidental opening. The other way is by applying the nature of physics.
One of the most common aircraft doors is the plug door. It can be seen on aircraft with pressurized cabins and is designed to take advantage of the difference between the cabin and atmospheric pressure. At high altitudes, the pressure inside the aircraft will be higher than that of the air outside, so the door seals itself in place as the aircraft flies.
There is no such pressure difference when the aircraft is on the ground, so the doors can easily be opened. However, this is only done by trained professionals like the cabin crew to prevent any incidents before or after take-off.
Opening cabin doors
Cabin doors can be opened in different ways depending on the type, but the first movement is always one of inward motion. After this, some will swing to the side, whereas others retract towards or even into the aircraft’s ceiling. However, it is essential to note that this only tends to be the case on passenger aircraft. After all, inward-opening cargo doors would reduce the space for cargo on a freighter.
Passenger doors are also equipped with emergency opening systems. On an aircraft like the Airbus A330, this includes an escape slide stored in a little box at the bottom of the door, a damper actuator that limits door travel during normal operations and acts as an actuator for automatic door opening during an emergency, and lastly, a slide arming lever.
In case passengers have to use the emergency slide, the door will be opened with the lever in the armed position, automatically inflating and deploying the slide. If the automatic system fails, a manual inflation handle can also be used to deploy the escape slide.
Can doors be opened mid-flight?
As we’ve already established, aircraft doors are designed to be used on the ground, where they are not subject to the pressure difference found at higher altitudes. Most of the time, flight attendants seamlessly operate these structures, allowing for the prompt dispatch of the plane at one end and an equally prompt disembarking process at the other.
However, we’ve heard cases of such doors being opened unintentionally and sometimes deliberately by unruly passengers. One of the most infamous incidents occurred in May when a passenger on an Asiana Airlines Airbus A321 opened one of the cabin doors at about 700 ft. While the plane still landed safely, about nine passengers were hospitalized after facing breathing difficulties.
This was a rare case, as such mischief is not usually achievable. This was only possible because the plane was flying at a low altitude, where cabin and atmospheric pressure start to level out. The airline further explained that the A321 is automatically set to adjust cabin pressure according to the aircraft’s altitude. This would not have been possible at 35,000ft.
The possibility of a regular passenger opening the door on the ground was witnessed on a Pakistan International Airlines Boeing 777 in 2019. A passenger mistook the cabin door for a bathroom while on the ground in Manchester. Because of the accidental emergency slide deployment that followed, the flight was delayed for seven hours.
Cockpit doors
The second most common door is probably the cockpit door, which has a totally different design. They have evolved over the years, becoming stronger and safer, especially after the 9/11 attacks in 2001. Today, they are made with various high-strength, lightweight composites capable of withstanding bullets and small grenades.
They have electrical locking latches and are controlled with a toggle switch, usually found on the captain’s right-hand side. During a flight, access to the cockpit can be requested by entering a unique pin on the keypad outside the door. A buzzer will sound, and pilots will decide whether to grant or deny access to the cockpit. Some doors even have cameras to see who is requesting access. In the case of smaller aircraft like the famous Cessna 172, the door is kept in place by a simple latch.
Source: simpleflying.com