Ejection seats are a type of in-cockpit motorised chair that, in an emergency situation, can rapidly propel themselves – along with their occupant – out of an aircraft.
The propulsion force is delivered by either the detonation of an explosive charge located under the seat or by rocket motor, with the ejection out of the cockpit occurring in two key stages.
The first stage involves the canopy/hatch of the cockpit being jettisoned or destroyed, clearing the area above the pilot’s head. For jettison-based systems, small charges around the canopy’s base are set off in order to release it from the fuselage, while destruction-base examples have an explosive cord embedded within the acrylic plastic of the canopy that shatters it milliseconds prior to the seat being launched.
The second stage, which occurs less than a second after the removal of the canopy, entails the seat itself being hurled upwards through the now open roof. Here a rocket motor or charge propels the chair up to a set altitude and then another small charge is blown to deploy a large, built-in parachute.
Although this is the most common ejection system, others also exist. Alternative varieties include those where the entire cockpit is ejected, others that fire the seat directly through the physical canopy to shatter it, and drag extraction systems, which utilise the airflow past the aeroplane to move the pilot out of the cockpit on a guide rail.