Speaker 1: Welcome to brain Stuff, a production of iHeart Radio, Hey
Speaker 1: brain Stuff Lauren vogelbone here. Back in the nineteen thirties,
Speaker 1: aviation manufacturer Boeing came up with a new airliner, the
Speaker 1: Model three oh seven Stratoliner, which featured a game changing innovation.
Speaker 1: It was equipped with a pressurized cabin, which enabled the
Speaker 1: plane to fly more swiftly and safely at altitudes above
Speaker 1: the weather without causing passengers and crew to have difficulty
Speaker 1: getting enough oxygen from breathing the thinner air at twenty
Speaker 1: feet or about six thousand meters. Since then, cabin pressurization
Speaker 1: has become one of those technologies that most of us
Speaker 1: who fly probably take for granted. Cabin pressurization works so
Speaker 1: well that passengers barely even notice it, in part because
Speaker 1: it gradually adjusts the air pressure inside the plane as
Speaker 1: it climbs in altitude, and then adjusts it again on
Speaker 1: the way down. Before the article this episode is based
Speaker 1: on how stuff works, spoke with Chuck Horning, who's been
Speaker 1: an associate professor in the Aviation Maintenance Science Department at
Speaker 1: em Very Riddle Aeronautical University since two thousand five. Before that,
Speaker 1: he was a mechanic and maintenance instructor at Delta Airlines
Speaker 1: for eighteen years. He explained that the basic technology of
Speaker 1: airplane pressurization has pretty much stayed the same for decades,
Speaker 1: though the advent of electronic computerized controls has made it
Speaker 1: more precise. Essentially, the aircraft uses some of the excess
Speaker 1: air that's pulled in by the compressors and its jet engines.
Speaker 1: He said, it's not a terribly complex system. The engines
Speaker 1: don't need all that air for combustion, so some of
Speaker 1: it is tapped off and used for both air conditioning
Speaker 1: and pressurization. The excess air from the compressors is cooled
Speaker 1: and then pumped into the cabin. It's regulated by a
Speaker 1: device called the air cabin pressure controller, which Corning describes
Speaker 1: as the brains of the pressurization system. He said that
Speaker 1: controller automatically regulates the pressure is sation. It knows from
Speaker 1: information that the flight crew enters in what the cruising
Speaker 1: altitude is, its schedules the pressurizing so that as the
Speaker 1: airplane climbs and the external pressure goes down, it goes
Speaker 1: to work. Pressurizing. An aircraft too much could put its
Speaker 1: main body. Also called the fuselage under too much stress
Speaker 1: from differential pressure inside and outside the fuselage as the
Speaker 1: plane climbs. To avoid that, airliners don't try to duplicate
Speaker 1: the air pressure at sea level. Instead, at a cruising
Speaker 1: altitude of thirty six thousand feet that's eleven thousand meters
Speaker 1: on most commercial jets, simulate the air pressure at an
Speaker 1: elevation of eight thousand feet, or about the same as
Speaker 1: Aspen Colorado. However, the Boeing seven eight seven Dreamliner, which
Speaker 1: has super strong carbon fiber in its air frame, is
Speaker 1: able to get down to the equivalent of air pressure
Speaker 1: at six thousand feet or eighteen Horning explained that's better
Speaker 1: because as the cabin altitude goes up, you have less
Speaker 1: oxygen in your blood. That's why when you get off
Speaker 1: a plane you may feel tired. We'd add that other
Speaker 1: factors of air travel, like dehydration and stress can add
Speaker 1: to that. But back to pressurization. How much air needs
Speaker 1: to be added in order to pressurize the cabin depends,
Speaker 1: of course, on the volume of the cabin, but it's
Speaker 1: more complicated than simple volume because the aircraft's pressurization system
Speaker 1: works in combination with the air conditioning system. It's also
Speaker 1: continuously cycling that air through the cabin, recirculating some of
Speaker 1: it and venting the rest as it draws in fresh
Speaker 1: air from the engine compressor. Most airplanes will completely exchange
Speaker 1: the air inside the cabin in three to five minutes.
Speaker 1: Airliners have to be careful to pressurize gradually as they ascend,
Speaker 1: and depressurize just as gradually when they descend towards the destination,
Speaker 1: because humans are pretty sensitive to change. Is an air
Speaker 1: pressure something anyone who's ever suffered from airplane air already knows.
Speaker 1: That's one reason why the air pressurization system has automated controls.
Speaker 1: As Horning explains, if the controller were to malfunction, the
Speaker 1: aircraft's pilot could manually depressurize the aircraft during the descent,
Speaker 1: but it might be an uncomfortable experience for passengers and
Speaker 1: crew since it's tough to do it deftly by hand.
Speaker 1: The air pressurization system also contains safety mechanisms designed to
Speaker 1: ward off mishaps, namely two pressure release valves. The positive
Speaker 1: pressure release valve will pop open if inside pressure gets
Speaker 1: too high because too much air is being pumped in
Speaker 1: the cabin. This release valve relieves that pressure. There's also
Speaker 1: the negative pressure valve, which protects the aircraft from the
Speaker 1: effects of a shift in which the outside pressure becomes
Speaker 1: greater than inside the cabin, it vents air in This
Speaker 1: might occur during a sudden descent, but it also occurs
Speaker 1: during normal operation. Horning said, airplanes are not designed to
Speaker 1: be submarines. They're designed to have a higher inside pressure
Speaker 1: than the outside. That's why the negative pressure relief valve
Speaker 1: is much more sensitive. As a result, when you're on
Speaker 1: a plane that's descending, once in a while, you actually
Speaker 1: hear a loud rush of air. That's the negative pressure
Speaker 1: valve kicking in. In the rare event that deep pressurization
Speaker 1: fails during a flight, there are other safeguards. There's a
Speaker 1: sensor that detects when the pressure declines to the equivalent
Speaker 1: of twelve thousand feet or thirty seven in elevation. That
Speaker 1: switch automatically drops oxygen masks into the cabin so the
Speaker 1: passengers can continue to breathe without difficulty. In some aircraft,
Speaker 1: the oxygen comes from cylinders, while others get it from
Speaker 1: generators that release oxygen through a chemical reaction. Today's episode
Speaker 1: is based on the article how are airplane cabins pressurized
Speaker 1: on how stuff works dot Com written by Patrick J. Tiger.
Speaker 1: Brain Stuff is production of by Heart Radio and partnership
Speaker 1: of how stuff Works dot Com, and it is produced
Speaker 1: by Tyler Clane. Four more pod casts from my heart Radio,
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