How Things Work: Ejection Seats
- By Mary Collins
- Air & Space magazine, July 2002
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.