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Emergency Descent - 36000'

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Emergency Descent - 36000'

Old 15th Jun 2013, 15:12
  #41 (permalink)  
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Quite right, Rat - indeed, risking heresy here, a rapid descent even to 20k and then more 'sedate' is going to be fine - look at the times of useful consciousness at 20, and as long as the drivers are on Oxy, a few dizzy pax would not be a major problem.
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Old 15th Jun 2013, 15:33
  #42 (permalink)  
 
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BOAC: Is not the problem not with the aircrew but with the passengers who are only supplied with supplemental O2 rather than O2 under pressure for the crew.
Any extended delay with a cabin altitude above 30,000ft. will be very bad for the passengers no matter how quickly they done the drop down masks. Thus the priority is to get the cabin altitude below 30,000ft.
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Old 15th Jun 2013, 15:36
  #43 (permalink)  
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Any extended delay with a cabin altitude above 30,000ft. will be very bad for the passengers no matter how quickly they done the drop down masks. Thus the priority is to get the cabin altitude below 30,000ft.
- read my post again?
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Old 15th Jun 2013, 16:31
  #44 (permalink)  
 
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For what it's worth I agree with BOAC, however in today's worlds of strict SOP's and less opportunity to demonstrate good airmanship, I imagine da management would have something to say about not executing a rapid descent to 10000 or within a few thousand feet of MSA if that were higher....

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Old 15th Jun 2013, 16:42
  #45 (permalink)  
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Yes, but I think Rat's point was is this 'box-ticking' or do we have a quiet think about it? After all, suppose you had an 'unavoidable' MSA of 15,000' the pax will not 'die'. They may be a bit light-headed, and cabin crew probably need to be taken care of here with bottled oxy, but that would be all.
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Old 15th Jun 2013, 16:58
  #46 (permalink)  
 
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BOAC: I was agreeing with you! I simply wanted to make the point that some of the other posters seemed to imply that there was no great rush to get down once "the crew were on O2" no matter how high the cruising altitude was.
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Old 15th Jun 2013, 17:06
  #47 (permalink)  
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BOAC: I was agreeing with you!
- ok then, it just didn't read that way!

To clarify, and I cannot recall my RAF decompression training now, but I think somewhere between 15 and 30 minutes of 'awake' at 20k without O2 and a heck of a lot longer alive, so no great rush in reality.
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Old 15th Jun 2013, 19:54
  #48 (permalink)  
 
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Excuse my ignorance, but what do you gain by slowing down the rate of descent?
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Old 15th Jun 2013, 21:04
  #49 (permalink)  
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See Rat post #41
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Old 16th Jun 2013, 13:07
  #50 (permalink)  
 
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I repeat, in real life ear drums have been burst by just such action.
I guess question has to be where does the the greatest risk lie?
Which is more likely? That a passenger or crew member bursts an eardrum or that someone is adversely affected by spending more time at a slightly higher altitude ?
It's not immediately obvious to me which is more likely but after thinking about it I think it's more likely that someone will suffer from a lack of oxygen. My reasoning is that I have dropped thousands of people out of aircraft who descend at about 10,000 fpm and I can't remember anyone bursting an eardrum, yet once a month or so someone on one of my flights requires oxygen because their body isn't coping with extended periods at 8000ft. So I think there is a higher chance of having passengers on board who would not cope with being at 12, 13 or 14,000ft, than of someone bursting an eardrum.
Does anyone have any examples or stats on burst eardrums during emergency descents?
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Old 16th Jun 2013, 16:07
  #51 (permalink)  
 
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I doubt the sky divers would be jumping if they had a cold. Many pax, even crew, fly when they have a slight cold. The auto cabin rate of descent can just about be survived with some nose blowing and swallowing. Sit next to a child who has not been taught this technique and watch their parents teaching them. Perhaps this was why in the olden days they used to dish out sweets at TOD. Anyway, having been in an a/c with a screaming pax who had a cold and whose head started to explode below 10,000' I've seen the result. Out of 100's of pax & crew i can be confident someone is likely to have dodgy ear tubes for whatever reason. Slowing down the ROD passing 14,000' should have no negative O2 effects on anyone.
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Old 17th Jun 2013, 01:21
  #52 (permalink)  
 
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I thought about that Rat but the cold scenario also impacts on the passengers ability transfer O2 in their lungs so I thought it cancelled out the argument to a degree. I'm not hard and fast on my opinion here, I just thought it worth while seeing if there were any examples in the real world of the eardrum burst. There are certainly many everyday examples of 8000ft cabin altitude being too much for some.
If you take those people who are not good at transferring O2 with reduced pressure, ( they're old, have a cold, smokers etc) and then give them 5-10 seconds of severely reduced pressure while they don their masks, then expose them to 13 or 14,000ft for a few minutes, I think you may well have some people in need of attention ( medical O2 ) from the cabin crew.

Of the examples of burst eardrums, how many burst as the air escaped their sinuses as opposed to bursting in the last 4000ft of descent as the thicker air entered their sinuses?
It's an interesting discussion.
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Old 17th Jun 2013, 01:26
  #53 (permalink)  
 
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To clarify, and I cannot recall my RAF decompression training now, but I think somewhere between 15 and 30 minutes of 'awake' at 20k without O2 and a heck of a lot longer alive, so no great rush in reality.
A heck of a lot longer is right.
Just for interests sake, all the passengers on Helios 522 were alive when the hit the ground and that had been hours at thirty something.
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Old 17th Jun 2013, 07:16
  #54 (permalink)  
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My take on Rat's original question was more "let's talk about it and see if there can be a shift in emphasis" on Emergency Descents rather than getting into minutiae about ToUC, colds, skydivers etc etc.

It is, as he implies, very much a 'box ticking exercise' as it stands.
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Old 17th Jun 2013, 07:24
  #55 (permalink)  
 
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Originally Posted by framer View Post
A heck of a lot longer is right.
Just for interests sake, all the passengers on Helios 522 were alive when the hit the ground and that had been hours at thirty something.
Weeeell, the lights may have been on but I'd doubt anyone was home.
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Old 17th Jun 2013, 07:45
  #56 (permalink)  
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Whoa! No-one is talking about cruising at 30k for 3 hours!! RAT asked why we scream straight down to 10k rather than, say, 14k and ease off.
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Old 17th Jun 2013, 11:07
  #57 (permalink)  
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If you take those people who are not good at transferring O2 with reduced pressure, ( they're old, have a cold, smokers etc) and then give them 5-10 seconds of severely reduced pressure while they don their masks, then expose them to 13 or 14,000ft for a few minutes, I think you may well have some people in need of attention ( medical O2 ) from the cabin crew.
Probably the only benefit one can ever get from smoking is better tolerance to hipoxia / better survival rate with low O2.

Comparisons of altitude tolerance an... [Aviat Space Environ Med. 1997] - PubMed - NCBI

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Old 17th Jun 2013, 19:27
  #58 (permalink)  
 
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Helios & TUC

Helios was a tragedy, a classic case of Swiss cheese. i'm still shocked the crew missed the pressure controls set to manual & failed to appreciate the very loud warning. Poor Systems knowledge rears its head again, with a dirty look in Seattle’s (Sorry, South Carolina) direction for using one horn for multiple warnings. -However, the fact everyone was alive highlights the problem -time of useful consciousness .
As far as the OP's father complaining about 'dust' in the masks; that is intentional and part of the engineering to ensure the masks do actually deploy. (it's called French Chalk)
An emergency decent is a well-rehearsed maneuver that (like a TCAS RA) requires positive but not 'panicked' response. Sounds like everything worked as planned; though i'm surprised no one’s raised the 'turn off the airway' chestnut....
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Old 17th Jun 2013, 20:31
  #59 (permalink)  
 
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'turn off the airway' chestnut....

Quote : " surprised no one has raised the 'turn off the airway' chestnut.... "


Not in UK airspace of course . . .
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Old 17th Jun 2013, 21:58
  #60 (permalink)  
 
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Thoughts.

Any time above 25000' cabin alt is bad, because above that there is a real chance of decompression sickness (BOAC - remember bends, chokes, creeps, staggers from the N Luffenham advanced farting course?) and any sub aqua fans on here know what decompression sickness means.

If you're not sure about 'structural damage' leave the IAS alone - you'll still get 4000fpm down (at least) and yr aiming for 10000' (so no more than 10 mins downwards), where the partial pressure of O2 is half that of sea level so a good place to be and not coincidentally the RAF limit of unpressurised flight.

Slow and methodical is good when it comes to initiating the descent - no prizes for rushing and getting it wrong; another 20sec won't hurt.

Don't ignore RA - the other guy won't and you get no more points (and therefore no more prizes) for an immaculate emergency descent which writes off two ac.

Pax comms (sorry OP) is the last thing to consider. Once it's all done (the 'and relax' moment) is the time to explain - let's hope all the pax have had the courtesy to listen to the briefing properly and when the masks descend "pull sharply etc etc etc". But if they haven't the chances are that they'll have fallen asleep and will wake up pretty quickly once at 10000'. On the other hand, if they haven't listened and yr over some seriously high ground they might not. SO PAX - listen to what the cabin crew tell you in the briefing.

Just my 2p worth - hope it helps
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