Blasted out at 20 times the force of gravity: what ejection from a fighter jet does to the body

Three US F-15E fighter jets were shot down over Kuwait in the early hours of Monday (March 2) in an apparent friendly fire incident during Operation Epic Fury, the joint US-Israel campaign against Iran.

All six crew members ejected safely and are in a stable condition – but “safely” is a relative term when you’re being blasted out of a stricken aircraft travelling at combat speed.

Decisions to eject are not taken lightly, but often only a few seconds are available to make that call – one that sets off a chain of events subjecting the body to some of the highest G-forces (the effect of acceleration on the body) a human can withstand. Waiting too long can be deadly. Some studies suggest delays are linked to death rates of up to 23%.

Fighter pilots can withstand up to 9G with the help of anti-G equipment, but even that can only be sustained briefly. Ejection from a fighter jet generates forces far beyond that. (To put the forces involved in context, most people lose consciousness at around 5G, because gravity’s effect surpasses the heart’s ability to pump blood to the brain.)

The seat is launched clear of the aircraft and then propelled upward to ensure enough altitude for a parachute to deploy safely, accelerating the occupant at up to 200m per second squared – roughly 20 times the force of gravity.

When used within the recommended parameters – the right speed, altitude and attitude (the aircraft’s angle or position in the air) – modern ejection seats show a greater than 95% survival rate.

Modern seats are known as “zero-zero”, meaning they can technically be used even if the aircraft is stationary on the ground. But low-altitude ejections below 500ft (152m) reduce survival to around 50%.

The ejection is just the beginning

Surviving the ejection is no guarantee of walking away uninjured. A large review of the evidence found major injuries occur in just under 30% of ejections, affecting the spine, limbs, head and chest.

Spinal fractures are the most common, occurring in as many as 42% of ejections, with the vertebrae at T12 and L1 (the lowest vertebra of the mid-back and uppermost vertebra of the lower back) accounting for nearly 40% of spinal fractures in a group of German aircrew.

The cushioning discs between the vertebrae absorb the same forces and can compress sharply, similar to the way the spine naturally squashes down during the day, causing most people to lose up to 20mm in height through normal daily compression.

The direction of ejection also matters. In normal flight, positive G-forces press the pilot into the seat, causing blood to move toward the lower body. Negative G occurs when the aircraft accelerates downward relative to the pilot, such as during a dive or when flying upside down, driving blood toward the head instead.

Ejecting under these conditions has been linked to eye injuries, probably caused by rapid pressure changes in the delicate blood vessels of the eye, and can result in temporary blindness lasting months.

Once outside the aircraft, the crew is hit by “windblast” – a violent rush of air caused by the jet’s speed. This can reach 600 knots in some circumstances, and there are recorded instances of ejection above the speed of sound.

At those speeds, masks and equipment can be ripped away – a serious problem at altitude, where oxygen masks are essential. Their loss can trigger hypoxia – a lack of oxygen that affects thinking and decision-making – reducing the crew member’s ability to manage their own survival.

High altitude also brings the risk of hypothermia and frostbite, depending on the location and conditions.

Fragments of the cockpit canopy can become embedded in exposed soft tissue – the neck is particularly vulnerable – while in more severe cases, aircraft parts or missile shrapnel can cause penetrating trauma to the liver, lungs and other structures, requiring emergency surgery.

If the parachute deploys successfully, the opening shock – the sudden deceleration as the canopy fills – can itself break ribs and dislocate shoulders, as well as cause injuries to the perineum (the area between the legs) from the harness. Around 49% of injuries in parachuting occur at landing, with the feet accounting for one-third of all injuries.

For those who land in trees rather than on the ground, the danger does not end there. Being suspended in a harness for any length of time carries the risk of suspension trauma – sometimes called “harness hang syndrome” – where blood collects in the legs and struggles to return to the heart and brain, leading to unconsciousness and, in some cases, death.

Recovery time for those who do come through it varies widely. Studies show that return to flying duties can take anywhere from one week to six months, depending on the severity of the injuries sustained.

Ejection remains far safer than attempting to survive a crash. For the six F-15E crew members recovering in Kuwait, surviving the ejection was only the first challenge.

Adam Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.