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Pressurisation/autopilot interlock

For those rare occasions ...
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There are several documented occurrences of "ghost flights" where the cockpit crew have succumbed to anoxia as a result of cabin depressurization, and the autopilot has kept the plane on course until it ran out of fuel and spun in, typically with the loss of all on board.

Pressurization (or oxygen) is needed for the non-acclimatised above about 5000m AMSL (acclimatised individuals can cope at considerably higher altitudes, up to 10000m).

There aren't many bits of your planet above 5000m, so it would be safe enough to link the cabin pressurization warning system to the autopilot. When the pressurization alarm sounds, if there is no "override" action within a set period, the altitude setting automatically defaults to 5000m. The aircraft makes a controlled descent to denser air where (hopefully) the crew will recover, and take appropriate action.

There is a risk that the aircraft might fly into terrain. But if something isn't done before the fuel is exhausted, that's going to happen anyway, so the risk is justified in this special circumstance.

8th of 7, Oct 21 2013

Ghost Plane http://en.wikipedia..._Airways_Flight_522
[bs0u0155, Oct 22 2013]

Chilling effects of hypoxia http://youtu.be/_IqWal_EmBg
[Klaatu, Oct 24 2013]

[link]






       Seems like this ought to be fairly obvious. Are we sure that modern systems don't do something like this already? I guess maybe the actual occurance of this is farely rare, so most pilots/airlines don't see a good cost/benefit ratio.
scad mientist, Oct 21 2013
  

       // Are we sure that modern systems don't do something like this already? //   

       Yes. It's not implemented in the Die-By-Wire software on any extant commercial transport, and definitely not on older airframes, although it would be a fairly simple autopilot mod.
8th of 7, Oct 21 2013
  

       I'm pretty sure the flying-into-mountains part could be avoided as well.
MaxwellBuchanan, Oct 21 2013
  

       //I'm pretty sure the flying-into-mountains part could be avoided as well.//   

       Absolutely. Don't let the South Americans, Pakistanis, Chinese or Nepalese have aircraft. The one or two remaining peaks over 5000m can be considered concentration aids.
bs0u0155, Oct 21 2013
  

       Given that there appear to be maybe a hundred points in the world above 5000m, I would have to agree. Admittedly, you're probably going to want to remain in the 4900-5000 meter range, since dropping below that increases the number of peaks greatly.   

       Of course, if the autopilot is smart enough to do that, can't it just signal the nearest airport with long enough runways and an autoland system, and bring itself down?
MechE, Oct 21 2013
  

       // if the autopilot is smart enough to do that //   

       The whole point about this is that it isn't smart at all. It's extremely dumb and simple.
8th of 7, Oct 21 2013
  

       //Of course, if the autopilot is smart enough to do that, can't it just signal the nearest airport with long enough runways and an autoland system, and bring itself down//   

       Or, first class passengers may select their preferred terrain to fly into.
bs0u0155, Oct 21 2013
  

       I like this idea. It seems simple to implement. Yet I could see a malfunctioning cabin pressure sensor, a malfunctioning altimeter, and pilots confused by the alarm resulting in controlled flight into terrain. I have no idea how these things are guarded against and no idea how rapid a descent would be needed to arrive at 5000 in time to prevent death/brain damage.
the porpoise, Oct 21 2013
  

       The big risk is from subtle incapacitation.   

       Explosive depressurization is hard to miss, what with all the symptoms - bleeding from the eyes and ears, loss of bowel control due to expanding intestinal gas, etc. and the flight crew are provided with oxygen masks.   

       However, a systems failure that drops the pressure slowly without generating an immediate alert is more dangerous. The pilots are deprived of oxygen before the alarm goes off; their decision-making capacity is impaired and their thinking processes slowed. When the alarm does trigger, they spend time trying to find out what's wrong instead of immediately going onto supplementary oxygen, and then pass out before disconnecting the autopilot.   

       You don't need a rapid descent. A 500 ft per minute glideslope from FL350 will put you back into "breathable" air where the crew have a good chance of spontaneous recovery in 20 minutes, and the moment the descent starts the air quality improves. 1000 fpm would be better, easily achieved without any aerobatics, just a matter of throttling back and dropping the nose slightly.
8th of 7, Oct 22 2013
  

       Slow depressurization with the wrong switch thrown was the culprit here <link>.   

       I think they've fixed the problem now.
bs0u0155, Oct 22 2013
  

       Write a letter to Boeing or Airbus. And Ask   

       "Dear Mr. Boeing:   

       I recently thought of a way to save one of your airplanes (and most of the people on board) . In a nutshell....
popbottle, Oct 22 2013
  

       //...bleeding from the eyes and ears, loss of bowel control due to expanding intestinal gas, etc...//   

       I'm guessing it happens the other way around, if holiday dinners at my house are any indication. Most of us would happily choose the mountain after that... [+]
Grogster, Oct 23 2013
  

       //it's extremely dumb and simple// [8th], I think you're forgetting (I know you know this stuff better than me) the minimum complexity of modern FBW systems.   

       A global digital elevation map of the necessary resolution (100m vertical, 1 degree horizontal) will fit in 64k of memory. You could literally do this off an 8048 microprocessor - that's the one which runs your keyboard - and have it take position data from best of [GPS | dead reckoning].   

       The FBW is *far* more complicated than that; if it fails, you're doomed to be a blood/aluminum/dirt mixture anyway.
lurch, Oct 23 2013
  

       //The FBW is *far* more complicated than that; if it fails, you're doomed to be a blood/aluminum/dirt mixture anyway//   

       The new generation of jets is changing all that though.... now there's slightly less fuel and a whole load of composites in there too!
bs0u0155, Oct 23 2013
  

       Yes, wonderful isn't it ? The gut-wrenching terror of dying because of an avionics system failure has now been knocked off top spot by that old favourite Catastrophic Structural Failure aided and abetted by In-Flight Fire. Makes the concerns about Pilot Error and ATC incompetence fade into the background by comparison ...   

       // "Dear Mr. Boeing: I recently thought of a way to save one of your airplanes (and most of the people on board) . In a nutshell.... //   

       "Dear Mr Aircraft Manufacturer,   

       We've been busily reverse-engineering the software in your flight control systems with a view to turning a civil airliner into a precision guided munition, when we had an idea ..."   

       No, we don't think so.
8th of 7, Oct 24 2013
  
      
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