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If the cabin depressurizes, the pilots immediately fly the plane down at a 45 degree angle to quickly move to an altitude with more hospitable air pressure. Peo

If the cabin depressurizes, the pilots immediately fly the plane down at a 45 degree angle to quickly move to an altitude with more hospitable air pressure. People who don't put on masks (and most people don't) regain consciousness after a couple minutes. The real safety hazard is anything that makes it harder to evacuate the plane, such as bulky clothing or eye-wear that make it harder to see in the dark or through smoke.

tyingq 6y ago
There's a transcript from a decompression event that shows what you're talking about here: https://fearoflanding.com/accidents/accident-reports/weve-lost-the-cabin-southwest-flight-812/ https://fearoflanding.com/accidents/accident-reports/weve-lo... I particularly like the "He's doing it anyway" comment. I imagine there are situations where they can't descend though.
- mcguire 6y ago
  The magic words: "declaring an emergency". On the other hand, even at 3000-4000 feet per minute, it can take a while to get from 35,000 to 10,000 ft.
  - hanniabu 6y ago
    I would think more than 10k would be sufficient considering the Everest base camp is around 18k feet, but of course the lower the better.
    - jcrawfordor 6y ago
      The point where hypoxia can set in varies from person to person, esp. when accounting for people with respiratory disorders. 10,000 feet is often considered a rough line where the altitude is no longer safe for everyone (that is, particularly susceptible people may begin to show symptoms), but the FAA progressively requires pressurization or supplemental oxygen from 12,500 to 15,000 feet. Altitude sickness (different from hypoxia but sometimes also quite severe) will occur below 10k in some people if there has been a rapid change in altitude, but fortunately it is much more survivable than hypoxia.
- qmarchi 6y ago
  There are some regions, like the Tibetan Plateau where the average elevation is actually higher than 10k feet, meaning an nosedive could technically have you hit a mountain.
  - groby_b 6y ago
    That would be why most airlines don't fly over the Tibetan Plateau :) If you really want nightmares about flying in that region, I recommend looking at the approach to Paro airport. 7.5k elevation, surrounded by 18k peaks, horrifying turbulences.
    - prepend 6y ago
      Lukla airport is really fun, it’s at 11k and mountains all around.
    - srean 6y ago
      IIRC till a few years ago only 4 pilots had authorization to land there. I was more scared while landing in Boston for the first time. It seemed to me that the aircraft was landing on the water, was not expecting that. https://www.youtube.com/watch?v=SbLHah4XUwk https://www.youtube.com/watch?v=SbLHah4XUwk (Paro landing)
  - cardiffspaceman 6y ago
    There are a few "av-geek" videos that cover operations of airlines in the vicinity of the Tibetan plateau, and they talk about how the pilots have to be qualified and trained for the fact that the plane is never at an altitude where people breathe easily. Even railroad operations require things like the availability of supplemental oxygen for passengers and crew.
  - kwillets 6y ago
    Cuzco is one. I think it's higher than the pressurization altitude.
    - joshvm 6y ago
- taloft 6y ago
  They’re going to be descending whether atc gives them permission or not. Keep in mind, Southwest has TCAS and already knows of nearby aircraft to a near certainty. The only real goals are get to breathable air and don’t hit anything. Passengers have minutes before they run out of air.
- deleted 6y ago
  [deleted]
leoh 6y ago
Interesting -- I wonder if depressurization masks could be used (and retrofitted if need be) during covid for safety
- cesarb 6y ago
  AFAIK, passenger oxygen masks on airplanes use a chemical oxygen generator, which only works for a few minutes before it's exhausted (the pilots use a different system with oxygen cylinders, and IIRC the rest of the crew has portable oxygen bottles).
K0balt 6y ago
It is true that you would max-rate descend to get to breathable altitudes, but FYI that will not be flying at a 45 degree angle lol. If you did try to fly an airliner down at a 45 degree angle, you would either have to do it with a falling-leaf stall after slowing to about 150kts (I doubt this is possible in an airliner?) or you would quickly break the speed of sound and the aircraft would disintegrate as the wings and stabilizers were ripped off. A max rate descent feels steep, but it's not that steep lol.
- AWildC182 6y ago
  They have spoilers which do allow a fairly steep angle, combined with other techniques can get you down very quickly, though not quite 45 dergees IIRC. Some transport aircraft like the C-17 can deploy thrust reverses in flight to achieve those attitudes. I'm told the people riding in back don't enjoy it though.
  - Traubenfuchs 6y ago
    Watching two people fight over specialized facts is fascinating. We readers have no clue what‘s true.
    - AWildC182 6y ago
      Fight might be a strong word... I should at least provide a little source material though: https://www.youtube.com/watch?v=lUUU-C-7o98 https://www.youtube.com/watch?v=lUUU-C-7o98 https://www.youtube.com/watch?v=Gdn0465zE4o https://www.youtube.com/watch?v=Gdn0465zE4o
    - jcrawfordor 6y ago
      I think the biggest issue is that the relationship between pitch attitude (angle) and rate of ascent/descent in aircraft is tenuous at best. During landing, for example, it is typical to have a healthy descent rate with the nose slightly up from level. I don't think I've ever seen any procedure with a fixed pitch angle, it pretty much always depends on the gross weight anyway. Emergency descent maneuvers in the C-172 and I believe many other small aircraft actually involve a 45 degree roll angle, and whatever pitch angle achieves a desired speed (e.g. 120 kias in the C-172). This produces a tight downward spiral, the spiral helps because it moves lift off the vertical axis which lets you descend more quickly at a fixed speed - otherwise you'll speed up until the wings fall off. I suspect the 45 degrees above may have come from confusion over which axis it was around. I'm not sure what the exact justification is for the choice of 45 degrees but 60 degrees roll angle is usually considered sort of the upper limit (beyond that is technically aerobatics) so 45 is pretty commonly considered the "steep" extreme. It looks like the procedure is different for the big boys. A quick google shows that the emergency descent procedure for the 747 is thrust closed, speedbrakes at flight position, gear down, make 320 kias. Pitch angle that produces would depend on weight but it's not going to be 45. No spiraling involved, but then 747 seems to (unsurprisingly) have a lower max bank angle (really max load factor) than smaller planes. The point is you wouldn't even really pay attention to the pitch attitude, you'd pay attention to airspeed. The answer to "what should the pitch be" is pretty much always "whatever results in the airspeed you want."
hkai 6y ago
45 degree angle, really.

tyingq 6y ago

There's a transcript from a decompression event that shows what you're talking about here: https://fearoflanding.com/accidents/accident-reports/weve-lost-the-cabin-southwest-flight-812/ https://fearoflanding.com/accidents/accident-reports/weve-lo... I particularly like the "He's doing it anyway" comment. I imagine there are situations where they can't descend though.

mcguire 6y ago
The magic words: "declaring an emergency". On the other hand, even at 3000-4000 feet per minute, it can take a while to get from 35,000 to 10,000 ft.
- hanniabu 6y ago
  I would think more than 10k would be sufficient considering the Everest base camp is around 18k feet, but of course the lower the better.
  - jcrawfordor 6y ago
    The point where hypoxia can set in varies from person to person, esp. when accounting for people with respiratory disorders. 10,000 feet is often considered a rough line where the altitude is no longer safe for everyone (that is, particularly susceptible people may begin to show symptoms), but the FAA progressively requires pressurization or supplemental oxygen from 12,500 to 15,000 feet. Altitude sickness (different from hypoxia but sometimes also quite severe) will occur below 10k in some people if there has been a rapid change in altitude, but fortunately it is much more survivable than hypoxia.
qmarchi 6y ago
There are some regions, like the Tibetan Plateau where the average elevation is actually higher than 10k feet, meaning an nosedive could technically have you hit a mountain.
- groby_b 6y ago
  That would be why most airlines don't fly over the Tibetan Plateau :) If you really want nightmares about flying in that region, I recommend looking at the approach to Paro airport. 7.5k elevation, surrounded by 18k peaks, horrifying turbulences.
  - prepend 6y ago
    Lukla airport is really fun, it’s at 11k and mountains all around.
  - srean 6y ago
    IIRC till a few years ago only 4 pilots had authorization to land there. I was more scared while landing in Boston for the first time. It seemed to me that the aircraft was landing on the water, was not expecting that. https://www.youtube.com/watch?v=SbLHah4XUwk https://www.youtube.com/watch?v=SbLHah4XUwk (Paro landing)
- cardiffspaceman 6y ago
  There are a few "av-geek" videos that cover operations of airlines in the vicinity of the Tibetan plateau, and they talk about how the pilots have to be qualified and trained for the fact that the plane is never at an altitude where people breathe easily. Even railroad operations require things like the availability of supplemental oxygen for passengers and crew.
- kwillets 6y ago
  Cuzco is one. I think it's higher than the pressurization altitude.
  - joshvm 6y ago
taloft 6y ago
They’re going to be descending whether atc gives them permission or not. Keep in mind, Southwest has TCAS and already knows of nearby aircraft to a near certainty. The only real goals are get to breathable air and don’t hit anything. Passengers have minutes before they run out of air.
deleted 6y ago
[deleted]

leoh 6y ago

Interesting -- I wonder if depressurization masks could be used (and retrofitted if need be) during covid for safety

cesarb 6y ago
AFAIK, passenger oxygen masks on airplanes use a chemical oxygen generator, which only works for a few minutes before it's exhausted (the pilots use a different system with oxygen cylinders, and IIRC the rest of the crew has portable oxygen bottles).

K0balt 6y ago

It is true that you would max-rate descend to get to breathable altitudes, but FYI that will not be flying at a 45 degree angle lol. If you did try to fly an airliner down at a 45 degree angle, you would either have to do it with a falling-leaf stall after slowing to about 150kts (I doubt this is possible in an airliner?) or you would quickly break the speed of sound and the aircraft would disintegrate as the wings and stabilizers were ripped off. A max rate descent feels steep, but it's not that steep lol.

AWildC182 6y ago
They have spoilers which do allow a fairly steep angle, combined with other techniques can get you down very quickly, though not quite 45 dergees IIRC. Some transport aircraft like the C-17 can deploy thrust reverses in flight to achieve those attitudes. I'm told the people riding in back don't enjoy it though.
- Traubenfuchs 6y ago
  Watching two people fight over specialized facts is fascinating. We readers have no clue what‘s true.
  - AWildC182 6y ago
    Fight might be a strong word... I should at least provide a little source material though: https://www.youtube.com/watch?v=lUUU-C-7o98 https://www.youtube.com/watch?v=lUUU-C-7o98 https://www.youtube.com/watch?v=Gdn0465zE4o https://www.youtube.com/watch?v=Gdn0465zE4o
  - jcrawfordor 6y ago
    I think the biggest issue is that the relationship between pitch attitude (angle) and rate of ascent/descent in aircraft is tenuous at best. During landing, for example, it is typical to have a healthy descent rate with the nose slightly up from level. I don't think I've ever seen any procedure with a fixed pitch angle, it pretty much always depends on the gross weight anyway. Emergency descent maneuvers in the C-172 and I believe many other small aircraft actually involve a 45 degree roll angle, and whatever pitch angle achieves a desired speed (e.g. 120 kias in the C-172). This produces a tight downward spiral, the spiral helps because it moves lift off the vertical axis which lets you descend more quickly at a fixed speed - otherwise you'll speed up until the wings fall off. I suspect the 45 degrees above may have come from confusion over which axis it was around. I'm not sure what the exact justification is for the choice of 45 degrees but 60 degrees roll angle is usually considered sort of the upper limit (beyond that is technically aerobatics) so 45 is pretty commonly considered the "steep" extreme. It looks like the procedure is different for the big boys. A quick google shows that the emergency descent procedure for the 747 is thrust closed, speedbrakes at flight position, gear down, make 320 kias. Pitch angle that produces would depend on weight but it's not going to be 45. No spiraling involved, but then 747 seems to (unsurprisingly) have a lower max bank angle (really max load factor) than smaller planes. The point is you wouldn't even really pay attention to the pitch attitude, you'd pay attention to airspeed. The answer to "what should the pitch be" is pretty much always "whatever results in the airspeed you want."

hkai 6y ago

45 degree angle, really.