Emergency Slides: How Do They Work?

Jul 12, 2023

The emergency slide is a system that allows for rapid passenger disembarkation in an emergency.

In the event of an emergency which requires passenger evacuation, time is of the essence. By regulations, the crew must be able to evacuate all the passengers within 90 seconds from the start of the evacuation process with half of the emergency doors or exits inoperative. This can be quite a task.

The emergency slide is a system that allows for rapid passenger disembarkation in an emergency.

The regulations state that if an emergency exit in an aircraft is above 1.8 m or 6 ft above the ground level, with the landing gear extended, it must have means to assist the passengers in evacuating the aircraft with minimum injuries. For this, the regulations say that a self-supporting slide or equivalent must be provided.

Similarly, for an overwing exit, if the aircraft wing is above 1.8 m or 6 ft, a slide or an equivalent egress system must be provided for the passengers.

According to EASA CS-25 SUBPART D – DESIGN AND CONSTRUCTION, the slides must fulfill the following requirements:

The slides are normally stowed in the slide stowage container of an emergency exit. As most passenger doors of the aircraft are also emergency exits, these doors also have a slide stowage.

In the simplest slide system, when the exit is armed, the slide deployment mechanism is triggered by a lanyard when the door is opened from the inside. This causes the slide to inflate using carbon dioxide stored under pressure stored in a cylinder. The cylinder passes the pressurized gas through flexible hoses, which are connected to an aspirator. This aspirator is equipped with flaps or small doors which automatically open due to the vacuum created by the high-speed air from the cylinder. This draws in ambient air from the atmosphere, which also helps in slide inflation.

The pressure of the cylinder can be viewed by an indicator on the slide stowage.

In normal conditions, the slide operation is fully automatic. However, in a situation where the system fails, there is a manual inflation handle located in the slide, which can be pulled to activate the slide.

A critical part of the flight is to ensure that the slides are armed for the departure, and at the same time, they must be properly disarmed before opening the doors after the flight to prevent an inadvertent slide deployment. Typically, one cabin crew member arms or disarms the door, which is cross-checked by another crew member. The pilots also have a view of the slide status in the cockpit instrumentation.

In the olden days, and still in some older aircraft, the arming and disarming of the slides is a highly manual task. In such aircraft, a retaining bar called a girt bar is used. When the doors are armed, the girt bar is fastened to floor brackets near the exit. And when the doors are disarmed, the girt bar is fastened to the door itself. The girt bar simply acts as a physical barrier that prevents the slide from moving out of its stowage triggering its inflation mechanism.

In modern aircraft, slide arming and disarming are done by a lever or a switch on the door. The crew is no longer required to physically move the girt bar. The movement of the lever mechanism arms or disarms the door. When in the armed position, the girt bar is moved away from the door and placed on the cabin floor. And when the lever is in the disarmed position, the girt bar prevents the slide deployment as it is attached to the slide stowage area.

In many aircraft, once the door is disarmed, a safety pin with a red tag is inserted into the lever mechanism. This locks the lever and prevents unintentional arming of the door.

When the door is opened from outside, it is designed such that there is automatic disarming of the door. There are also systems that warn a person if he or she tries to open an armed door. This can be in the form of a light or an alarm, or both.

In a ditching scenario, the slides can be used as rafts. It is important to note that not all slides can be used as rafts. An easy way to identify slides that are also rafts is by judging their size. Raft slides are dual lanes and thus are larger and wider.

The slide raft is attached to the door frame by using a daisy chain mechanism. To release the raft from the door frame, this daisy chain must be released - for that, a pull handle is provided. Once the handle is pulled, the daisy chain unwinds, and the raft is released from the door attachment. This does not fully detach the slide raft from the aircraft, as there is a ditching line fixed between the door frame and the raft.

In a ditching, particularly in the open sea, the fuselage of the aircraft will eventually sink. If the line remains attached to the aircraft, the raft might be pulled by the fuselage as it sinks. To prevent this from happening, the crew or those onboard must cut the ditching line. For this, a small knife is stowed in the raft near the ditching line. Once the line is cut off, the raft is released from the aircraft.

As a passenger, you are not trained to jump off a slide. It may seem simple enough, but there are small things that you can do to minimize injuries.

First off, before you jump, you must cross your hands on the chest and keep them that way until you reach the end. This prevents the hands and arms from dragging on the slide as you jump, which can cause burns.

The next thing that you must not do is wait before you jump. Keep in mind that in an evacuation, many of your fellow passengers will be behind you, and the crew is trying to get all of them out. If you wait, you are prolonging the evacuation. In such conditions, the crew are trained to forcefully push you onto the slide. You must not take it personally because, at the end of the day, they are trying to save your life.

The last thing is the most important. Once you are on the ground after the jump, you must immediately move to the side. The reason is that if you wait in the way of the other passengers, they will come and hit you, causing injuries. In a planned evacuation, there will be a crew or an assigned person to pull you or guide you if you get stuck in the pathway.

Journalist - An Airbus A320 pilot, Anas has over 4,000 hours of flying experience. He is excited to bring his operational and safety experience to Simple Flying as a member of the writing team. Based in The Maldives.