5.1 Aircraft Exits: Types, Certification & General Knowledge
Key Takeaways
- Transport aeroplanes are certificated by demonstrating that the full occupant load can be evacuated within 90 seconds using no more than half the available exits.
- Exits are classified by size and location, including floor level Type A, B and C doors, and Type I, II, III and IV exits, with overwing exits typically Type III.
- Most large aircraft doors are plug-type: cabin pressure forces the door against its frame, so the door must be moved inward or rotated before it can open.
- Door assist systems use a pressurised bottle or spring mechanism to open and hold the door in high wind, and are a source of severe injury if the door is operated incorrectly.
- Every exit is checked before flight for slide arming status, viewport clarity, handle and placard condition, clear escape path, and serviceable adjacent emergency equipment.
Why exit knowledge is examined so heavily
Nig. CARs 8.14.11.1 requires the operator to determine the cabin crew requirement for each aircraft type in order to effect a safe and expeditious evacuation. The number of exits, their size and their location are the reason the crew complement is what it is. Everything else in cabin safety training funnels into one measurable outcome: getting everyone out.
The 90-second demonstration
Transport aeroplanes are certificated by a full-scale demonstration in which the maximum certificated occupant load, using a representative mix of ages and sexes, evacuates the aircraft in darkness within 90 seconds, using no more than half of the available exits — because in a real accident some exits will be unusable. Nig. CARs Part 9 contains provisions for emergency evacuation demonstrations, including ditching demonstrations, using the AOC holder's own assigned cabin crew.
Two implications matter operationally:
- Half the exits is the design assumption. If a crew member assesses their exit as unusable, the plan already accommodates that; the correct action is to redirect passengers, not to force an unusable exit.
- Ninety seconds is the whole budget. Post-accident fire can render a cabin unsurvivable in about that time. There is no allowance in the certification basis for retrieving baggage, and this is the reason the evacuation command explicitly orders passengers to leave everything behind.
Exit classification
| Class | Typical location and access | Examples |
|---|---|---|
| Type A | Largest floor level door, at least 42 in wide | Wide-body main deck doors |
| Type B / Type C | Floor level doors, progressively smaller | Many narrow-body and regional doors |
| Type I | Floor level door, at least 24 in wide | Smaller transport aircraft |
| Type II | May be floor level or over the wing, slightly smaller | Regional aircraft |
| Type III | Over-wing exit, typically hatch-type, stepping over a sill | Boeing 737, Airbus A320 family overwing exits |
| Type IV | Over-wing, smaller, with a higher step-up and step-down | Smaller aircraft |
| Other | Tailcone exits, ventral airstairs, cockpit exits, flight deck sliding windows and escape ropes | Boeing 727 tailcone, various types |
Cabin crew must know their own aircraft's exit configuration precisely: how many exits, of what type, on which side, which are crew-operated, which are passenger-operated, and which are equipped with slides or slide-rafts.
How a door works
Most large aircraft main doors are plug type. The door is larger than its aperture and seats against the frame from inside, so cabin differential pressure forces it more tightly closed. It therefore cannot be opened while the cabin is pressurised, which is a fundamental safety feature and the correct answer to the recurring passenger question about opening a door in flight. Opening requires the door to be moved inward or rotated before it can be swung or lifted clear.
Typical operating sequence in normal mode, with variations by type:
- Confirm the slide is disarmed and the indication confirms it.
- Check the viewport for obstructions, ground equipment and personnel.
- Confirm the cabin is depressurised and any door-not-ready indication is clear.
- Move the operating handle through its full travel in the direction of the arrow.
- Allow the door assist to take the door, guiding rather than pushing.
- Latch or gust-lock the door in the fully open position before releasing it.
Door assist systems use a pressurised bottle or a powerful spring to drive the door open and hold it against wind. They are a major injury source: a crew member who fights the assist, or who stands in the path of a door that is being driven open, can be thrown out of the aircraft or crushed. Follow the type-specific technique exactly.
Slide arming status: the highest-consequence routine action
Every floor level exit fitted with a slide has an arming mechanism — a girt bar engaged into floor brackets, or a lever selected to ARMED or DISARMED — with a visual indication.
- Armed for departure: opening the door deploys and inflates the slide automatically.
- Disarmed for arrival at stand: the door opens without deploying the slide.
Arming and disarming is performed on command, cross-checked by another crew member, and confirmed to the senior cabin crew member. An inadvertent slide deployment injures ground staff, damages the aircraft, takes it out of service and is a reportable occurrence; a door armed when it should be disarmed, or disarmed when it should be armed, is one of the most consequential mistakes in cabin operations, which is why the cross-check exists.
Pre-flight checks at every exit
- Slide arming status correct for the phase, and the indication legible and consistent.
- Slide pressure gauge — where visible, needle in the green operable band.
- Viewport clean and unobstructed, with the exterior visible.
- Door handle, placards and instruction decals present, legible and undamaged.
- Manual inflation handle present in its stowage and unobstructed.
- Escape path clear — no baggage, catering, service items or passenger belongings in the door area or aisle.
- Adjacent emergency equipment present and serviceable: life vest, flashlight, PBE, extinguisher, and the door-area first-aid or survival equipment carried on the type.
- Overwing exits — hatch handle cover intact, placards legible, and the exit-row seats occupied only by passengers meeting the exit-seating criteria.
A defect at an exit is reported at once. An exit that cannot be relied on changes the evacuation plan for the whole cabin.
What is the certification standard that drives exit provision and cabin crew numbers on transport aeroplanes?
Why can a plug-type door not be opened while the aircraft is pressurised?
A crew member is about to open a door in normal mode on arrival. Which check most directly prevents an inadvertent slide deployment?
Which exits on a Boeing 737 or Airbus A320 family aircraft are typically Type III?