How Things Work: Ejection Seats

  • By Mary Collins
  • Air & Space magazine, July 2002
 

 

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    LAST DECEMBER, WHEN AN airman on a mission to Afghanistan initiated the ejection sequence on a B-1 bomber that was going down over the Indian Ocean, all four crew members blew out of the airplane in less time than it takes you to read this paragraph.

    They ejected at four different times and at four different angles so they wouldn’t hit each other while clearing an airplane that, crippled by “multiple malfunctions,” was going more than 600 mph at 15,000 feet.

    “It was the most violent thing I’ve ever felt in my life,” says one of the B-1 crew members, whom the Air Force asked me to identify as “Captain IROC.” “I lost a full inch in height,” because his spine absorbed such tremendous G-forces.

    “At 600 mph there’s tremendous aerodynamic pressure pushing down on you,” says John Hampton, engineering manager of the Goodrich ACES II ejection seat, the model that saved the lives of the B-1 crew. “There’s literally a couple thousand pounds pushing on your body, which is why you get banged up a bit.”

    Captain IROC might be a tad shorter, but he’s still around to chat. Here’s why.

    When a pilot pulls his ejection seat’s handle, which is located either between his legs or on one or both sides, depending on the cockpit arrangement, an electrical pulse signals thrusters to unlock the hatch, then rotate it up and out into the air stream. In the case of the B-1, the explosion ripped open four hatches, one for each crew member.

    Two pitot tubes (one for backup) on the side of the seat measure aerodynamic pressure to assess the speed of the airplane. A port behind the seat back measures ambient air pressure to determine the altitude. A central processing system—either digital or analog—takes this data and makes a calculation to determine which of three possible modes to activate. (Navy fighter jet seats, like the Martin-Baker NACES, can have up to five options.)

    Airplanes flying at low altitudes and low speeds will use a different sequence from that of  jets flying at high speeds and high altitudes. For example, F-22s, which use the ACES  II seat, will sometimes cruise at 50,000 feet, where there’s not much oxygen. The seat supplies supplemental oxygen, but because the pilot needs to get down to thicker air as rapidly as possible, the main chute doesn’t open right away. Instead, a smaller chute called a drogue deploys to stabilize the seat so it doesn’t tumble and to slow the pilot’s horizontal velocity. In a near free-fall, he plummets until he hits an altitude of 15,000 feet, at which point his main parachute automatically deploys.

    LAST DECEMBER, WHEN AN airman on a mission to Afghanistan initiated the ejection sequence on a B-1 bomber that was going down over the Indian Ocean, all four crew members blew out of the airplane in less time than it takes you to read this paragraph.

    They ejected at four different times and at four different angles so they wouldn’t hit each other while clearing an airplane that, crippled by “multiple malfunctions,” was going more than 600 mph at 15,000 feet.

    “It was the most violent thing I’ve ever felt in my life,” says one of the B-1 crew members, whom the Air Force asked me to identify as “Captain IROC.” “I lost a full inch in height,” because his spine absorbed such tremendous G-forces.

    “At 600 mph there’s tremendous aerodynamic pressure pushing down on you,” says John Hampton, engineering manager of the Goodrich ACES II ejection seat, the model that saved the lives of the B-1 crew. “There’s literally a couple thousand pounds pushing on your body, which is why you get banged up a bit.”

    Captain IROC might be a tad shorter, but he’s still around to chat. Here’s why.

    When a pilot pulls his ejection seat’s handle, which is located either between his legs or on one or both sides, depending on the cockpit arrangement, an electrical pulse signals thrusters to unlock the hatch, then rotate it up and out into the air stream. In the case of the B-1, the explosion ripped open four hatches, one for each crew member.

    Two pitot tubes (one for backup) on the side of the seat measure aerodynamic pressure to assess the speed of the airplane. A port behind the seat back measures ambient air pressure to determine the altitude. A central processing system—either digital or analog—takes this data and makes a calculation to determine which of three possible modes to activate. (Navy fighter jet seats, like the Martin-Baker NACES, can have up to five options.)

    Airplanes flying at low altitudes and low speeds will use a different sequence from that of  jets flying at high speeds and high altitudes. For example, F-22s, which use the ACES  II seat, will sometimes cruise at 50,000 feet, where there’s not much oxygen. The seat supplies supplemental oxygen, but because the pilot needs to get down to thicker air as rapidly as possible, the main chute doesn’t open right away. Instead, a smaller chute called a drogue deploys to stabilize the seat so it doesn’t tumble and to slow the pilot’s horizontal velocity. In a near free-fall, he plummets until he hits an altitude of 15,000 feet, at which point his main parachute automatically deploys.

    At low altitudes a pilot doesn’t need to free-fall, so the main parachute opens immediately and the drogue stays in its case. All of the decisions based on speed, altitude, and the weight of the passenger are already made for the pilot before he even clears the aircraft.

    Manufacturers have spent decades perfecting all the steps necessary for a fully automated ejection. A hole blows open overhead. The wind surges in. The pilot can feel the chemical cartridge ignite under his seat, which activates a catapult that pushes his seat up a rail. One-tenth of a second after yanking the handle, he’s out of there. As he clears the airplane a rocket system called STAPAC kicks in. The wind wants to flip the seat around like a milkweed seed, but the thrust from STAPAC offsets the rotation and keeps the seat and pilot upright and forward facing.

    About two seconds after the seat is rocketed upward, the parachute opens, and that triggers a bell crank that pulls the pins on the seat belts so the seat falls clear of the pilot. After all the bang and rush, the airman drifts quietly for three or four seconds. Then a survival kit drops on a 25-foot line. Upon contact with the water, the kits’ raft and life vest automatically inflate.

    While the success rate for ejections has improved dramatically since the 1940s, from about 50 percent to approximately 90 percent today, flailing limbs can get torn off by  600 mph winds, and ejection delays often shorten descents, and that increases the riskiness of the parachute landings. Women pilots, who weigh on average 50 pounds less than their male counterparts, are especially at risk because the lighter the object, the faster the toss and the greater the oscillation.

    But even in the most extreme conditions, if a pilot doesn’t wait too long, the ACES II can usually pull off a save. When Captain Jon Counsell had to eject from an F-15C on a training run over the Gulf of Mexico in 1995, he was going Mach 1.4, beyond the accepted parameters for success on the ACES II, which draws the line at 600 knots (690 mph). His limbs flailed so violently during the ejection that he broke his left arm, fractured his left leg in five places and dislocated both knees. Doctors thought he’d never walk again, but seven years later he’s back in the cockpit. In an exchange with the Navy, he now flies F/A-18s.

    “I had to make one decision—to pull the handle,” he says. “After that, 13 automatic functions had to work perfectly for me to live, and they did.”


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