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In an emergency, an aircraft should be evacuated in less than 90 seconds with half the exit doors inoperable. Time is certainly of the essence, and in recent times we have seen that this rarely occurs. Manufacturers have to prove their aircraft can be evacuated in 90 seconds through testing, although one could say that this rule needs to be reviewed and retested under more realistic circumstances. Passenger education is also needed to understand that taking baggage slows the evacuation, therefore risking the lives of other passengers and also the crew who leave the aircraft last, after checking that there are no passengers still onboard.
Baggage can also damage and puncture the slide. Whether a Boeing or Airbus aircraft, door operation and the evacuation slide are critical to safety, with speed in an evacuation without the need for airstairs or ground equipment. However, any crew member will say there is a big difference in how 
Boeing and Airbus doors operate.
How A Slide Is Deployed
During an evacuation, flight attendants deploy emergency slides, which are attached to either the door or the door frame, depending on type. Both Boeing and Airbus main cabin exits are plug-type doors but operate in a very different way. They cannot be opened during pressurized flight. Depending on the aircraft type, there may also be overwing exits that operate in a different manner. The slides are stowed in containers attached to the main cabin doors and are either in the armed or disarmed position. In the disarmed position, the door can be opened safely.
According to Smithsonian Magazine, when the door is opened from the inside and the door is armed, a lanyard triggers the slide deployment mechanism. Carbon dioxide is stored in a cylinder under pressure, which causes the slide to inflate. The pressurized gas passes through flexible hoses connected to an aspirator, which has small doors that open due to the vacuum created by high-speed air from the cylinder. This then draws in ambient air outside, which also helps the slide inflate.
The pressure of the cylinder can be viewed by an indicator on the slide stowage. Slide deployment is automatic when the door is armed, but if it fails to inflate, there is a manual inflation handle on the right-hand side of the slide. The slide can take between six and 10 seconds to inflate to its full extent.
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Operating A Boeing Door On The 737
On many Boeing aircraft, the 737 being the classic example, arming the door is a more physical, hands-on task than on the comparable Airbus. The difference comes down to how each manufacturer connects the escape slide to the aircraft. On the Boeing, arming the door means that the flight attendant must physically move the girt bar, which is a metal bar at the bottom of the folded slide. This is picked up by hand and detached from its stowed brackets on the door, and latching it into a fitting on the cabin floor.
This means that when the door is opened, the slide is dragged out and inflates. The next step is placing a red warning streamer across the window to show that it is armed and is visible both inside and outside. That manual transfer is combined with an arming lever that swings across the door and can be heavy and awkward to operate from a crew point of view. Disarming reverses the process, moving the girt bar back off the floor and onto the door. The girt bar prevents the slide from moving out of its storage and triggering inflation.
Boeing doors operate by pulling slightly inward and then swinging outward horizontally so that the exterior of the door meets the exterior of the fuselage. The interior of the door is seen when standing outside the aircraft. Airstairs should always be in place before a crew member opens or closes a door, and the safety strap should be engaged when the door is open.
The Airbus Difference
Airbus streamlined the door operating process rather than manually shifting a girt bar. The crew simply follows a “PIN–LEVER–PIN” sequence. The safety pin is removed from its hole next to the arming lever, the arming lever is moved into the armed position, and the pin is placed in its stowage. The mechanism internally engages the slide, with no bar to lift or reposition. There are also additional indicators on the door and on the floor that show that the door is armed.
Airbus also builds in a safety backup that 737 doors lack. If an armed Airbus door is opened from the outside, a mechanical linkage automatically disarms the slide to prevent it from deploying and potentially injuring ground crew. There is also a ‘slide-armed’ warning light which flashes if someone tries to move the door operating handle. Boeing relies more heavily on the human step being done correctly.
Airbus main doors operate upwards and outwards, and the door slides parallel to the fuselage. The interior of the door faces the exterior of the fuselage. There is a helper mechanism that makes operation smoother and less heavy. Airbus has a power-assist system that functions through a mechanical and gas-charged actuator mechanism on the main passenger entry doors to rapidly push and lock the door open during an emergency evacuation.
Inadvertent Slide Deployment
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The emergency slides are designed to be deployed quickly during an emergency evacuation to get everyone off the aircraft as soon as possible. However, sometimes mistakes can be made, and crew can mistakenly or inadvertently inflate the slide. This happens when the door is opened and is still in the armed position. It is quite rare but still happens from time to time. Once the slide has started to deploy, it cannot be stopped and can be dangerous to anyone in the vicinity due to its powerful inflation mechanism.
This can happen when crew do not check that the door is disarmed before opening. Crew members may be rushed to depart, be fatigued, or be distracted by passengers. Airbus estimates that there are 30-40 cases every year on their aircraft worldwide. These are mostly at the forward left entrance door and the rear right loading door. Crew often operate both Boeing and Airbus types, which can sometimes cause confusion as not all doors are the same type.
If doors are not properly disarmed on arrival, the slide could be deployed inadvertently (by mistake). This could cause injury to ground staff or equipment and is also extremely expensive to repack (between $25,000 and $50,000), according to Aerodynamiks. An inadvertent slide deployment can cause injuries to ground staff, incur high costs to repack the slide, and delay the flight. According to Airbus, the minimum cost of an event involving a 90-minute ground delay is estimated at around $11,000. If it leads to a flight cancellation and a requirement to accommodate passengers in hotels is needed, the cost can rise as high as $200,000.
Procedures & Practices
Once boarding is complete, the doors are closed, and the aircraft is ready to leave the stand, the flight crew will announce, “cabin crew, arm the doors and cross-check.” Another variation on this is “cabin crew, doors to automatic and cross-check.” This means the doors will be armed and ready, and the slide will be automatically attached to the door frame. So, if an emergency were to occur, the slides would automatically inflate as soon as the door is opened.
The crew member will arm the door by moving the arming lever to the armed position. This action places the girt bar and attaches the slide. They will then check visual indicators, which vary depending on aircraft type. There may be a visual indicator on the door and one on the floor. Each opposite crew member then checks the same indicators on their colleague’s door to ensure they are both armed and verbally confirms “cross-check.” The cross-check procedure reduces the chance of error.
Disarming the doors takes place on the command, “cabin crew, disarm the doors and cross-check” or “Cabin crew, doors to manual and cross-check.” The arming procedure is then completed in reverse. The cross-check procedure confirms that the doors are disarmed and visual indicators are checked on the Airbus doors and the red streamer removed from the 737 door. On the Airbus, the senior crew member can check the status of the doors on the flight attendant panel as well as confirm status with each crew member by interphone, before reporting to the flight deck.
The Bottom Line
The overall take is that the Boeing door demands more manual manipulation and physical strength to arm, while the Airbus door reduces it to a lighter, more foolproof lever action. Ask almost any crew member which they prefer, and they will say the easier A320 door over the heavy, clunkier 737 door.
The primary design difference between the emergency exit doors of the A320 and the 737 involves their opening motion. On the Airbus, doors operate outward and parallel to the fuselage, whilst on the Boeing, doors swing inward and crosswise before rotating out. Both are plug-type doors under cabin pressure and cannot be opened during flight.
On the 737, the door is heavy and requires manually attaching the girt bar and slide to the aircraft when armed. The A320 is much easier to operate, with a lighter overall door weight and helper mechanisms to make manual door operations easier and smoother. It also uses a pin-lever-pin process to make arming and disarming the door easier.
