YOU have a one in three chance of breaking your spine – but you are trading a violent event for probable death, says Swinburne University researcher in aviation medicine David Newman. As a civilian pilot and former Royal Australian Air Force doctor, Dr Newman explains this ”escape mechanism of last resort”.
Walk us through it.
The modern ejection seat is a complex, two-part system. There’s an ejection gun, which the pilot activates by pulling a handle and that gets the seat moving up out of the aeroplane. Once the seat travels a metre or two up, the secondary device kicks off.
A rocket, basically, directly under the seat. It’s a series of little white tubes, with nozzles for the exhaust outlet, which have solid rocket fuel in them. That burns for about 0.2 of a second.
Rocketing the seat how far?
Roughly 100 feet in the air, depending on the seat and aircraft configuration. Then a tiny drogue parachute pops out of the seat-top. It’s not enough to land with but it stabilises the seat so the pilot doesn’t tumble out of control.
When comes the bigger chute?
If it’s below 10,000 feet, once the drogue chute activates it pulls out the main parachute at the same time as the ejection-seat mounting points are disengaged from the pilot’s harness. So the seat falls away and the pilot is left floating under the main chute. The sequence is less than three seconds from pulling the handle to being under the chute – it’s very quick, violent and people clearly remember doing it.
And at higher altitude?
If you eject at 20,000-30,000 feet, you don’t want the main chute to open straight away because it could take 20 minutes to get to the ground and there’s not enough oxygen to breathe. For the pilot to breathe there’s a small oxygen bottle attached to the seat. Now, the pilot’s fall out of the sky is fast – terminal velocity, almost – but a barometric-pressure device will sense when the seat is at 10,000 feet.
Yes, then the main chute comes out, the seat falls away and pilot floats down for a relatively firm landing. The parachute is designed to get you on the ground quickly with minimal injury.
OK, what is your chance of survival?
If you look at statistics around the world, the survival rate is greater than 92 per cent. So a small number of ejections are fatal, usually because the pilot leaves it to the last minute to eject, or the seat is damaged, in a midair collision for instance.
Are injuries common?
About one in three will get a spinal facture, due to the force when the seat is ejected – the gravitational force is 14 to 16 times normal gravity and it might be applied at 200G per second. Bruising and abrasions are typical from the shock of the chute opening or the air blast. In the early days, there were cases where pilots would eject into very-high-speed air and it would whip their arms behind and break them, pop their shoulders out; same thing could happen to the legs.
What about neck injuries?
People have hit their chins on their chest. The weight of a standard head, plus helmet, plus mask, is about seven kilograms. At 9G it is 63 kilograms of mass. If you have a 25G ejection, with a standard seat-back angle, the force driving your head forward and down is about eight times the force of gravity. There is also a risk of leg fracture.