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In their most basic form, ejection seats are a pilot’s survival kit. For those one in 10 seats that are used in an emergency, they allow the pilot to escape and survive a plane crash or any other air disaster. But, today, the single idea of escaping and surviving is not enough. The seats have to meet high standards to make sure they don’t cause any injuries, while designs also have to keep up to speed with aircraft technology as planes becomes faster and more technically advanced.
Michael Cameron is the senior after sales executive for UK ejection seat manufacturer Martin-Baker. He says: “Once upon a time, there was an argument that no matter what the injuries, the pilot should be grateful just to be alive as a result of ejection. But that’s not the case now. We are trying to reduce every aspect of the ejection risk.” Cameron says that one of the main aims with an ejection seat is that the pilot must have to do minimal actions to eject. Pulling a single lever should set in motion a series of events that cause the seat, carrying the pilot, to safely eject out of the plane, the parachute to open and the seat to be released from the pilot before they start their descent to earth.
A typical ejection sequence for one of Martin-Baker’s seats, the MK10, starts with the pilot pulling the seat firing handle, positioned between their legs. This causes gas from a seat initiator cartridge to pass to the harness power retraction unit (HPRU), which operates and pulls the pilot into the correct posture prior to ejection. This is important as it prevents any injury to the pilot’s body, particularly the spine, during the forces of up to 16G. Meanwhile, gas passes to the main gun where another cartridge fires and the seat unlocks from the aircraft. This gas pressure causes the seat to rise up a set of guide rails towards the aircraft canopy. The canopy is then cleared, either by the seat breaking through it, or by an explosive chord fragmenting, or the canopy being jettisoned.
At a fixed distance, a rocket pack underneath the seat is fired to maintain the thrust of the initial cartridge so that the seat is safely ejected above the aircraft. A device called a barostatic time release unit (BTRU) then ensures that the seat and pilot are separated at a given time and altitude as the parachute opens. A normal parachute descent follows for the pilot and the seat drops to earth. The process from pulling the handle to being on the end of the parachute takes a mere two seconds.
During the past 20 years, the ejection seat, and the way it works, has funda-mentally stayed the same. But as aircraft have become more advanced with increased speeds and manoeuvrability, the need for quicker escape times has become necessary. As a result, Cameron says that ejection seats must now be cost-effective, meet or exceed customers’ specifications and be comfortable. “We have to design seats that are very easy to maintain, very comfortable and very resilient,” he says. “Crew comfort is paramount now and also reducing the risk of the injury during the actual ejection phase.”
One way that quicker escape times have been achieved is by replacing mechanically-initiated units with ones that are electronically-initiated, using electronic sequencing and digital timing. Martin-Baker’s JF-17 ejection seat, which is used by the Pakistan Air Force, has a seat with an electronic system and uses a process that halves the usual two-second timeframe to eject. Cameron says: “Electronics are a lot more reliable than they used to be and there is so much that can be done with them. Instead of having clockwork mechanisms, we are going for electronic mechanisms for a primary decision maker. And that has proved very successful.”
As aircraft capabilities have increased, there is less time, in some planes, for the pilot to react in an emergency. There is also the risk, particularly with a military aircraft, that the pilot may be injured or unconscious and unable to eject at all.
Automatic ejection is being looked at as a way to resolve such problems. Cameron says: “We are looking at making the human more benign and doing more and more for them, including, if possible, automatic ejection. It’s an interesting concept.” He also says the company is likely to try and speed up the ejection process even more. “We’re down to one second now. Can we get it any quicker? Maybe,” he says.