The mechanics behind ejection seats may seem complex, but they are designed to save pilots' lives in emergencies. Although pilots rarely need to eject, in critical situations, pulling the ejection handle is often the difference between life and death.

Though the act of ejecting from an aircraft is something most pilots hope never to face, it remains one of the most vital safety mechanisms. Pilots in military planes or research aircraft rely on ejection seats to escape imminent danger when their aircraft becomes too damaged or otherwise unusable to remain in flight.

Ejecting from a plane traveling at supersonic speeds—faster than the speed of sound—can be incredibly perilous. At these speeds, the force of the ejection could subject the pilot to more than 20 Gs. This means the pilot's body is subjected to a force 20 times heavier than gravity itself, which can cause severe injuries or even fatalities.

Military jets, NASA experimental aircraft, and even some small commercial planes are equipped with ejection seats to give pilots a fighting chance in the event of an emergency. In this edition of Mytour, you’ll explore the components that make an ejection seat function, how it ejects a pilot from the aircraft, and the science behind the entire process.

Take a Seat

Ejection seats are crucial for various aircraft, especially when they are damaged during combat or testing, requiring the pilot to eject for their survival. These seats are among the most intricate systems on any aircraft, often containing thousands of components. Their primary function is clear: to propel the pilot safely out of the aircraft, then deploy a parachute to ensure a safe landing on the ground.

To truly grasp the mechanics of an ejection seat, one must first understand the essential components within the system. Every part must function flawlessly in rapid succession to ensure the pilot’s safety. A single malfunction in any critical component could lead to disaster.

Ejection seats are mounted in the cockpit and are typically connected to rails with rollers on the seat's edges. During an ejection, these rails direct the seat out of the plane at a precise angle. Like any standard seat, the ejection seat has a basic structure that includes a bucket, backrest, and headrest, around which other parts are designed. Below are some key devices integral to the ejection seat’s function:

When an ejection occurs, the catapult launches the seat along the rails, the rocket boosts the seat higher, and the parachute opens to ensure a safe descent. In some systems, the rocket and catapult functions are combined into a single mechanism. These seats also serve as restraint systems for crew members, both during an ejection and under normal conditions.

Ejection seats are part of a larger system known as the assisted egress system, where "egress" refers to a means of escape. A crucial element of this system is the aircraft's canopy, which must be jettisoned before the ejection seat can be activated. Aircraft without canopies are typically equipped with escape hatches on the plane’s roof, which blow off just prior to the seat’s activation, providing an escape route for the crew.

There are various ways to activate an ejection seat. Some seats feature pull handles positioned on the sides or at the center of the seat. In other designs, the seat is triggered when the crew member pulls down a face curtain to shield and protect their face. In the next section, we’ll explore what happens once the seat is activated.

Bailing Out

When a crewmember pulls the handle or yanks the face curtain down on the ejection seat, it starts a chain reaction that launches the canopy off the aircraft and ejects the crewmember to safety. The entire ejection process takes no more than four seconds, depending on the seat type and the crewmember’s body weight.

Pulling the ejection handle activates an explosive cartridge in the catapult, propelling the seat into the air. As the seat rises along the guide rails, a leg-restraint system is engaged, preventing the crewmember’s legs from being injured by debris. An underseat rocket motor provides additional force to elevate the crewmember to a safe height, a force that remains within normal human physiological limits, according to documents from Goodrich Corporation, a company that manufactures ejection seats used by the U.S. military and NASA.

Before the ejection system is activated, the canopy must first be jettisoned to allow the crewmember to exit the cockpit. There are at least three methods to detach or clear the canopy, enabling the escape:

Along with the crewmember, the seat, parachute, and survival gear are ejected from the aircraft. Many seats, like the Goodrich ACES II (Advanced Concept Ejection Seat, Model II), are equipped with a rocket motor beneath the seat. Once the seat and crewmember clear the cockpit, the rocket motor provides additional lift, propelling the crewmember another 100 to 200 feet (30.5 to 61 meters), depending on the individual's weight. This extra propulsion helps clear the aircraft’s tail. By January 1998, the ACES II system had been used for 463 ejections globally, according to the U.S. Air Force. More than 90% of those ejections were successful, with 42 fatalities recorded.

Once the crewmember exits the aircraft, a drogue gun in the seat fires a metal slug that pulls a small drogue parachute from the top of the seat. This parachute slows the descent rate and stabilizes the seat’s altitude and trajectory. After a certain period, an altitude sensor triggers the deployment of the main parachute from the pilot’s chute pack. At this moment, a seat-man-separator motor activates, causing the seat to detach from the crewmember. The person then continues to descend as with any typical parachute landing.

Modes of Ejection

In the ACES II ejection seat developed by Goodrich Corporation, three different ejection modes are available. The mode chosen is based on the aircraft's altitude and speed at the time of ejection. These parameters are measured by the environmental sensor and recovery sequencer, both located at the back of the ejection seat.

The environmental sensor tracks both the airspeed and altitude of the seat and transmits this data to the recovery sequencer. As the ejection sequence initiates, the seat ascends along the guide rails and activates pitot tubes, named after physicist Henri Pitot. These tubes are designed to measure changes in air pressure to determine the airspeed. The sequencer then processes this data to select one of the three ejection modes:

Physics of Ejecting

The process of ejecting from an aircraft is a violent series of actions that exposes the body to extreme forces. The main elements that influence an aircraft ejection are the forces and acceleration experienced by the individual, as explained by Martin Herker, a former physics educator. To calculate the force acting on the individual being ejected, we must apply Newton's second law of motion, which indicates that the acceleration of an object is determined by the force applied to it and the object's mass.

Newton's second law can be expressed as follows:

Force = Mass x Acceleration

(F=MA)

In the case of a crewmember ejecting from a plane, M stands for the combined mass of the individual and the ejection seat. A refers to the acceleration caused by the catapult and the underseat rocket.

Acceleration is measured in G's, which represent gravity forces. Ejections from aircraft can generate anywhere from 5 to 20 G's, depending on the ejection seat. As explained earlier, 1 G is the force of Earth's gravity and correlates to our weight. One G of acceleration is equivalent to 32 feet per second (9.8 m/s), meaning that an object dropped from a height will fall at this rate.

Determining the mass of the seat and attached equipment is straightforward. The largest factor is the pilot's mass. For instance, a 180-pound individual experiences 180 pounds of force under normal conditions. However, in a 20-G ejection, this same person will feel the equivalent of 3,600 pounds of force. To explore more about force, click here.

"To find the speed of the ejection seat at any given time, one must solve the Newton equation by factoring in the applied force and the mass of the seat and occupant. Additional details, such as the duration of force application and any initial velocity, are also necessary," explains Herker on his website about the physics of ejections. Herker's equation for calculating the seat's speed is as follows:

Speed is the product of Acceleration and Time, plus the Initial velocity

V(final) = Acceleration x Time + Initial velocity

Initial velocity refers to either the rate of ascent or descent of the aircraft. It can also be determined during the initial phase of the ejection procedure in a seat that integrates an explosive catapult with an underseat rocket. The velocity of the seat must be sufficient to separate the seat and occupant from the aircraft rapidly, ensuring they clear the entire aircraft.

Ejection seat usage is always a last-resort action when an aircraft is damaged and the pilot has lost control. However, the priority of saving pilots' lives surpasses that of saving aircraft, and at times, an ejection is necessary to preserve a life.