When squadron leader Douglas Davie of the RAF bailed out of a crippled jet on 30 July 1943 he had no choice in the matter: the tremendous jet-assisted g forces simply hurled him out of the cockpit as his plane spun out of control. The controls had jammed on his Gloster E28, the testbed for Britain's spanking new jet engines, plunging the plane into a high-speed, spinning dive. But before Sqn Ldr Davie could attempt to bail out at 33,000 feet, the canopy glass shattered and the gyrating plane jettisoned him into a 20,000-foot freefall - stripping him of his boots, helmet and oxygen mask in the process. Fortunately he was able to breathe by sucking on his severed oxygen tube and open his parachute - and he survived with only a touch of frostbite.

His luck wouldn't hold. Five months later, on 4 January 1944, the savage forces associated with emerging high-speed jet-powered flight would become more apparent still. Davie, a test pilot with the Royal Aircraft Establishment in Farnborough, UK, was flying the prototype of Gloster's twin-engined jet fighter, the Meteor, when one engine completely disintegrated on a high speed test run at 20,000 feet, leaving the aircraft hurtling out of control. As he tried to bail out, Davie's left arm was severed trying to open the canopy - possibly due to it snapping shut in the windblast. Astonishingly, he still managed to get out - only to be critically injured, or knocked unconscious, by the aircraft's tailplane as he tried to leap clear. Unable to open his parachute he plummeted to the ground, falling through the roof of the RAE.

But Davie did not die in vain. His gruesome experience threw into sharp relief the dangers pilots faced as jet engines made planes capable of speeds approaching 600mph (960km/h). Faster aircraft meant the pilot risked striking the vertical tail fin, or the horizontal tailplane, as they bailed out. What's more, loss of control at high speed boosts the forces the pilot must fight both when trying to discard the canopy and get out of the cockpit. Finally, the devastating effect of the slipstream wind blast at such speeds can break flailing limbs even if the pilot does manage to jump clear.

The Davie accident appalled the Air Ministry - which had seen too many combat crews lost in this way - and prompted it to seek a way for pilots to escape from jets. It was a move which helped create the explosively-fired, rocket-assisted ejector seats that have saved thousands of aircrew lives since the dawn of the jet age. Within mere seconds of deciding their aircraft is kaput, a pilot can be dangling safely from a parachute. Even so, ejector seats remain a work in progress: surveys show survival rates are 89%, and 51% for ejections performed below 500 feet – and aviation medicine experts believe more can still be done technologically to improve on those figures.

Pioneering pair

The Air Ministry was forced to act because the inability to escape crippled jets had seriously hit morale among the pilots of RAF Fighter Command, which was preparing to bring Meteors into front-line service. So the ministry sought ideas for an aircrew escape system from its regular technology suppliers – including the Martin-Baker Aircraft Company of Denham, Buckinghamshire, run by James Martin, a garrulous Ulsterman and a self-taught, self-made engineer.

An inveterate inventor, Martin patented gadgets in many different fields of endeavour. Fish fryers, bicycles with rain-proof hoods, tool sharpeners, quick-build trucks, three-wheeled cars and machine gun ammunition feeds number among his many inventions, according to Sarah Sharman’s biography of the engineer. In 1934 he went into the plane-building business with a flight instructor called Valentine Baker (who, by the way, just happened to be the pioneer aviator Amy Johnson's flight instructor).

Martin's first move into pilot safety came in December 1940 when Fighter Command asked him to develop a jettisonable canopy for the Supermarine Spitfire, which was prone to jamming during the frenetic dogfights of the Battle of Britain. Martin's answer was simple and effective: a red rubber ball dangling from the canopy pulled cables that unlocked restraining pins around the unit - instantly casting the canopy off into the airstream. It became standard on all Spitfires.

Meanwhile, Germany had been quietly developing ejector seats from 1939 onwards with its own fast propellor, jet and rocket plane programs in mind. On 13 January 1942 a Luftwaffe test pilot called Helmut Schenk ejected from an out-of-control Heinkel He 280, also an early twin-jet prototype, using a compressed air-powered ejector seat that shot up and out of the cockpit on rails. And by the autumn of 1944 the British Air Ministry was receiving bizarre reports of sightings of German pilots "being fired into the sky" from crashing German jets, Sharman says.

Explosive cartridges

"Despite its crude and unconventional design, the Heinkel ejection seat saved dozens of pilot lives during the war," write Kyle Keller and John Plaga of the US Air Force Research Lab at Wright-Patterson Air Force Base in Ohio, in a technical paper. It was an analysis of Heinkel seats captured by the US Army, say the authors, that led to the US developing its own ejector seats at around the same time.

Sweden’s Saab was also developing ejector seats and had in 1942 successfully ejected a crash test dummy from one of its Saab17 aircraft – but using a seat launched by a much more energetic device than a compressed air cylinder: an explosive-filled cartridge.

With his experience of airplane armaments, Martin thought the explosive cartridge much the better option for getting a pilot clear of the tailfin as quickly as possible. But he faced a dearth of physiological data: how big could you build the explosive charge that shoots the pilot into the air, without causing serious whiplash damage to them?

There was only one way to find out: Martin-Baker built a number of rigs to test the effect of the upward compressive thrust on the body of a seated man shot up a near-vertical path. They would then measure the accelerations and rates of rise of g involved and quiz the subject about how they felt. The first rig comprised a 4.8m-high (16 foot) metal tripod with a pair of seat guide rails fitted to one of the legs. The seat was driven by telescopic tubes "energised by an explosive cartridge".

Tests with a 91kg (200lb) dummy load worked well but what was really needed was a man – and a brave Martin-Baker aircraft fitter called Bernard Lynch stepped up.  Lynch would later act as the guinea pig in 30 aircraft ejections, mainly in Gloster Meteors.

"Bernard Lynch undertook the first live ride, being shot up the rig to a height of 4ft 8in. In three further tests, the power of the cartridge was progressively increased until a height of 10ft (3m) feet was reached, at which stage he reported the onset of considerable physical discomfort," the company says.

‘Massive explosion’

The handlebar-mustachioed Lynch was feeling back pain when pulling a mere 4g - so Martin began studying the human spine, including observing surgical operations on them, in a bid to understand its limitations. Indeed, Sharman’s biography reveals that Martin's secretary was shocked to receive human spine parts from a surgeon friend of Martin's, dubbing them "ghastly bits of body".

The first ejector seats, which fired the pilot using only an explosive cartridge (or a pair of them), were hard on the spine. Modern seats - whether they are the British, American or Russian types - further reduce the vertical g pulled on the ejectee by having the ejection gun only just powerful enough to get the pilot clear of the tailfin. At that point, a pack of rocket motors take over, taking the seat a further 60 metres (200ft) higher.

It wasn’t always like this. Former RAF flight lieutenant Craig Penrice, a member of the Royal Aeronautical Society who comments on ejection issues, knows that all too well. In 2003 he was flying a 1950-era Hawker Hunter back from an airshow in Portrush, Northern Ireland when both its electrical system and its engine failed over the Welsh coast. For the second time in his flying career, he had to eject. "There was a huge, massive explosion and I felt the most enormous force on my behind. The pain in my back felt like I had been hit by a plank of wood."

He ended up with a burst fracture of one of his vertebrae and fragments of bone embedded in his spinal cord - temporarily paralysing him from the waist down. "I'm still not 100%," he says.

The ejector seat in the Hunter - built in 1956 - predated the addition of rocket assist and was an all-explosive-cartridge model, known colloquially as a "bang seat" to pilots. "They function with a single cannon shot that gets you clear of the tail. The modern ones have a much lower impact gun because the rocket takes over to gradually accelerate you," Penrice says.

The UK Air Accidents Investigation Branch agreed: "These seats are of necessity somewhat harsher in operation than 'rocket seats'."

Under pressure

Another injury-relevant complication is the orientation of the plane and the pilot at ejection. In the summer of 1966, David Eagles was a naval aviator with the Fleet Air Arm on the carrier HMS Victorious. His Blackburn Buccaneer pitched nose up immediately after leaving the catapult - and did not stop pitching up. "So I told the guy in the back to eject and then I went," he says.

"It felt like a sharp jab in the back. It was all over in a flash. I crushed three vertebrae in my back and I was on a bed for some months." And that was with a rocket-assisted seat. "The single bang used to flatten spines. The rocket seat is a lot softer," Eagles says.

"Jimmy Martin told me later – as he wrote to all ejectees – that my injury could have been due to me ejecting while leaning to one side. The aircraft dropped a wing as it stalled and was banking to one side. That would have placed my vertebrae under pressure before the ejection."

Modern seats add the all-important capability of a "zero-zero" bailout - zero altitude, zero speed, according to Wing Commander Matthew Lewis, an accident investigator at the RAF Centre of Aviation Medicine at RAF Henlow in Bedfordshire in the UK. In other words, the pilot could still escape and get to high enough an altitude to open their parachute even if the aircraft is motionless on the runway.

So what is actually happening after a pilot, fearing death, activates the ejection seat? The ejection process is entirely automatic once the pilot pulls the activation handle - which is either above their head, between their legs or at the side of one (or both) legs. The above-the-head handle can also pull down a fabric face screen - invented by Martin - to both position the pilot's head and neck correctly and shield their face from windblast as they exit the cockpit.

As the cord is pulled, the canopy is dislodged in one of three ways, says Lewis. "You can jettison the whole canopy with small rockets that are attached to its edges. Or you can use a zig-zag of miniature detonating cord that's built in to the canopy to shatter it, with the windblast removing the pieces. Or you can use 'through-canopy ejection' - in which the seat headbox uses two spikes to shatter the canopy as it takes off."

"But through-canopy ejection has injury risks and we don't like it as the primary method in the RAF," he says.

Windblast threat

The ejection gun will pull between 12 and 15g on the pilot for about 0.15 seconds as they clear the tailfin. Then the rocket pack kicks in. At that point a small 1.5 metre (5 ft) drogue parachute is fired from a gun, stabilising the seat motion. If the ejection is at, say, 40,000 ft, the air is too thin for the chute to inflate - and it would risk tangling. So a pressure sensor called a barostat only lets the drogue chute pull out the main parachute when the seat is below 10,000 ft (3,000m).

All of it is controlled by a carefully choreographed automatic sequence – the pilot has to do nothing. "The ejection is so quick – from pulling the ejection handle to being on the end of a fully deployed parachute can take maybe 2.5 to three seconds, depending on the type of seat," says Lewis.

"The critical thing in terms of injury and the forces upon you is the windblast. Stick your arm out of a car window at 70mph (110km/h) and you get a bit of a blast backwards. Do that at 600knots (1,110km/h) and it's a different ball game."

To cater for that risk, ejector seats now have arm and leg restraints – effectively robotic garters around your calves that activate and hold your leg in the best possible position to prevent limbs flailing in the windblast. A mechanism built into the flight jacket does likewise, holding the arms tightly against your torso. "It stops the air blast ripping them to the side," says Lewis.

Another risk – though rare – is the mass of modern hardware attached to the head, such as head up display helmets and night vision systems, which can lead to neck injuries if the windblast catches them.

Vectored thrust seats?

Currently, Lewis says, about 25-30% of ejectees suffer back problems, due to the force of the explosive ejection gun cartridge forcing the pilot to slump forwards suddenly. "They typically get what's called an anterior wedge compression fracture, in which the front portion of the vertebral bone gets squished into a wedge-shape. They do actually heal up though and most people return to flying."

Lewis agrees that latter-day ejection seats are doing their job, but as an aviation medic he would like to see a safe escape offered in more challenging scenarios. "For instance, if you eject when inverted just 20ft (6m) feet off the ground, you'll hit the ground. A rocket pack offering vectored thrust could let you go sideways and then up to an altitude where you can open the 'chute."

Meanwhile, UTC Aerospace Systems of Colorado Springs, Colorado - Martin-Baker's US rival - is developing smarter ejection seat rocket motors for its latest seat, the Aces 5. Its idea: that the thrust provided will vary depending on the weight of the pilot. Lighter female pilots should not be getting the same seat launch thrust as heavier men, for instance - so their seat will vary that thrust intelligently by changing the rocket burn profile.

While all improvements will be welcome, for those at the sharp end, the ejector seat has already been a godsend.

"Being among the group of 160 or so pilots who have ejected twice I feel particularly fortunate,” says Penrice.  "If it wasn't for the ejector seat I wouldn't be here."

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