Rapid Depressurization
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Rapid Depressurization
Just wondering- is it possible to have a rapid depressurization in say a B737 WITHOUT having structural damage?
Also, in case of a rapid depressurization requiring an emergency descent from say 41000ft, what average descent rates would you get at (Mmo/Vmo)?
We have 12 minutes of passenger O2 in the back (the B737) so we should need just about 2500 fpm.... to get to 10,000ft from 41,000ft. We have a procedure requiring an initial descent to 22000ft in 4mnts 30 secs (from the loss of pressurization), level off and maintain 22000ft (due to enroute terrain) for a further 6 mnts, then descending to 10000ft in the remaing 1mnt 30 secs... Thats 8000 fpm!!!!
Or am I just calculating this all wrong?
Thanks FWW
Also, in case of a rapid depressurization requiring an emergency descent from say 41000ft, what average descent rates would you get at (Mmo/Vmo)?
We have 12 minutes of passenger O2 in the back (the B737) so we should need just about 2500 fpm.... to get to 10,000ft from 41,000ft. We have a procedure requiring an initial descent to 22000ft in 4mnts 30 secs (from the loss of pressurization), level off and maintain 22000ft (due to enroute terrain) for a further 6 mnts, then descending to 10000ft in the remaing 1mnt 30 secs... Thats 8000 fpm!!!!
Or am I just calculating this all wrong?
Thanks FWW
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I think there could be some cases when you won't have structural damage:for ex dual bleed trip off (very remote ,i think) ,malfunction of the pressurization system ,of the outflow valve...
I don't think you can achieve bellow 22000' a ROD of 8000',maybe if you lower the gear,but I guess it won't be achievable.I'll try it next time on the sim.You actually do this on sim?
Brgds Alex
I don't think you can achieve bellow 22000' a ROD of 8000',maybe if you lower the gear,but I guess it won't be achievable.I'll try it next time on the sim.You actually do this on sim?
Brgds Alex
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We appeared to have a 737 enter Ground Mode in the climb and were alerted by the cabin altitude horn (which was also the Take Off Configuration Warning horn). This resulted in the outflow valves motoring towards open and the cabin depressurising. We managed to stop the cabin rising above 14,000' but it was close- the masks were on the point of dropping out. It can happen.
Only half a speed-brake
I cannot speak about different regulations but JAR - OPS1 in fact asks for livable altitude before O2 runs out (less than 50% pax, let's keep it simple) that is 14000 and once it is gone for 10000 ft in thirty minutes. I get a feeling that other regulations sound similar.
Hence you have 42 minutes to get to FL100 but have to manage FL140 before pax oxy runs out. However the scenario you suggest still asks for a very demanding profile. If someone wanted to fine tune this extremly improbable case I would suggest investing in more detailed maps to get you out of FL220 sooner.
Hence you have 42 minutes to get to FL100 but have to manage FL140 before pax oxy runs out. However the scenario you suggest still asks for a very demanding profile. If someone wanted to fine tune this extremly improbable case I would suggest investing in more detailed maps to get you out of FL220 sooner.
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alexban: "I don't think you can achieve bellow 22000' a ROD of 8000',maybe if you lower the gear,but I guess it won't be achievable.I'll try it next time on the sim.You actually do this on sim?"
: Nope. We haven't done this particular profile on the sim. But on our regular depressurization drill we are averaging about 2500 to 3000fpm i think. (I am trying to get a more accurate figure from our sim instructors or maybe at my next sim ride). But I felt the same: 8000fpm does seem rather optimistic.
Flight Detent: "If someone wanted to fine tune this extremly improbable case I would suggest investing in more detailed maps to get you out of FL220 sooner."
: Our performance department has managed to get hold of some pretty accurate topographical maps of the region(crtsy the Military). The problem is that the grid MORA in the region is 25400ft. So the flight path to follow in case of a depressurization is defined, and the path crosses a peak of height 21370ft. We are supposed to be 22000ft there. Infact which brings up the question whether we need to clear mountainous terrain by 2000 ft in case of an emergency descent as well? I'm personally thinking that we need to probably install 22mnts of O2 capacity which would permit a higher intermediate level-off altitude.
alexban: "I think there could be some cases when you won't have structural damage:for ex dual bleed trip off (very remote ,i think) ,malfunction of the pressurization system ,of the outflow valve..."
: In case of a dual bleed trip the actual rate of cabin climb is just about 500-600fpm in a new aircraft(delivery testing at boeing) and maybe 1000fpm in case of older aircraft- not much more (hopefully )
Reasons for rapid depressurization without structural failure : Window failure. Outflow valve failure to open position in flight. Any more thoughts?
Rainboe: Great job done
All: thanks for your thoughts.
Many happy landings.....
: Nope. We haven't done this particular profile on the sim. But on our regular depressurization drill we are averaging about 2500 to 3000fpm i think. (I am trying to get a more accurate figure from our sim instructors or maybe at my next sim ride). But I felt the same: 8000fpm does seem rather optimistic.
Flight Detent: "If someone wanted to fine tune this extremly improbable case I would suggest investing in more detailed maps to get you out of FL220 sooner."
: Our performance department has managed to get hold of some pretty accurate topographical maps of the region(crtsy the Military). The problem is that the grid MORA in the region is 25400ft. So the flight path to follow in case of a depressurization is defined, and the path crosses a peak of height 21370ft. We are supposed to be 22000ft there. Infact which brings up the question whether we need to clear mountainous terrain by 2000 ft in case of an emergency descent as well? I'm personally thinking that we need to probably install 22mnts of O2 capacity which would permit a higher intermediate level-off altitude.
alexban: "I think there could be some cases when you won't have structural damage:for ex dual bleed trip off (very remote ,i think) ,malfunction of the pressurization system ,of the outflow valve..."
: In case of a dual bleed trip the actual rate of cabin climb is just about 500-600fpm in a new aircraft(delivery testing at boeing) and maybe 1000fpm in case of older aircraft- not much more (hopefully )
Reasons for rapid depressurization without structural failure : Window failure. Outflow valve failure to open position in flight. Any more thoughts?
Rainboe: Great job done
All: thanks for your thoughts.
Many happy landings.....
Only half a speed-brake
We had similar dealings with flying over from Black to Caspic Sea. Grid MORA over 14000 a lot and it had been suggested here that custom made maps may be provided with higher density grid so you do not get a 60x30 NM large chunk of airspace blocked when it is not necessary.
Further investigation revealed that you can actually cross the area in FL 100 on airways so luckily we've avoided all the stepped descent scenarios.
I know our big colleagues cross Iran/Pakistan only with these scenarios but still they definitely have more than 12 min. I wonder if the denser grid would be of any use such area.
Further investigation revealed that you can actually cross the area in FL 100 on airways so luckily we've avoided all the stepped descent scenarios.
I know our big colleagues cross Iran/Pakistan only with these scenarios but still they definitely have more than 12 min. I wonder if the denser grid would be of any use such area.
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FlightDetent: Maybe a larger scale map would provide a better picture esp if we were VMC, but then the problem would of how to avoid a peak in IMC? 
Or maybe if we can get a radial from some VOR that gives a track over the relatively lower ground.... definately worth a look.....
Any ideas on needing 2000ft clearance over mountainous terrain during a rapid descent due to a decompression?
Or maybe if we can get a radial from some VOR that gives a track over the relatively lower ground.... definately worth a look..... Any ideas on needing 2000ft clearance over mountainous terrain during a rapid descent due to a decompression?
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I had an ouflow run to the fully open position passing FL330 in the climb.
SCCM came in to flightdeck a few moments before to tell us that the cabin/galley curtain was "blowing in to the cabin".
We started the change from climb to descent and she had no sooner left the flightdeck than the cabin started it's dramatic climb!!
We got all the warnings as the cabin climbed through 10K but still managed to get the aircraft below the altitude the masks deploy before they popped out. We descended more than 19000ft in less than 3 minutes.
Close run thing, but we managed it; probably helped having just done a couple of sims with a depressuriastaion scenario a couple of weeks before.
SCCM came in to flightdeck a few moments before to tell us that the cabin/galley curtain was "blowing in to the cabin".
We started the change from climb to descent and she had no sooner left the flightdeck than the cabin started it's dramatic climb!!
We got all the warnings as the cabin climbed through 10K but still managed to get the aircraft below the altitude the masks deploy before they popped out. We descended more than 19000ft in less than 3 minutes.
Close run thing, but we managed it; probably helped having just done a couple of sims with a depressuriastaion scenario a couple of weeks before.
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Some snippets
Similar to Rainboe, I've also had the cabin depressurise in the cruise - because of a faulty gear squat switch. The aircraft was suddenly convinced it was on the ground, and one of the results was the cabin dumped all the pressure.
Flyinwithoutwings: You might want to look closer at your emergency descent next time you are in the sim; you quote 2500 fpm - for us, that would be a slightly expidited normal descent, whereas an emergency descent is well in excess of 4000 fpm.
The available oxygen increases quickly as you descend, and depending on the oxygen equipment, rate of consumption of the supplemental oxygen reduces as well. Once you pass 22,000 descending, you can take your time getting to 10,000 because the amount of suplementary oxygen you need at, say 14,000, is practically speaking negligible. (This is not to say that you or your passengers can be oblivious to a pressure altitude of 14,000 feet - they will get a headache, have difficulty sleeping, feel hot, and struggle to complete the crossword. Your passengers will however not die at 14,000 feet, even if you stay there for an hour).
Flyinwithoutwings: You might want to look closer at your emergency descent next time you are in the sim; you quote 2500 fpm - for us, that would be a slightly expidited normal descent, whereas an emergency descent is well in excess of 4000 fpm.
The available oxygen increases quickly as you descend, and depending on the oxygen equipment, rate of consumption of the supplemental oxygen reduces as well. Once you pass 22,000 descending, you can take your time getting to 10,000 because the amount of suplementary oxygen you need at, say 14,000, is practically speaking negligible. (This is not to say that you or your passengers can be oblivious to a pressure altitude of 14,000 feet - they will get a headache, have difficulty sleeping, feel hot, and struggle to complete the crossword. Your passengers will however not die at 14,000 feet, even if you stay there for an hour).
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I should be noted that the Everest comparison is a bit of a red herring. Those climbers manage to live and function at that altitude only after several weeks of intense and painful acclimitization above 17,000 ft. You can't walk straight up Everest in one shot without some adaptation.
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As part of the production flight test schedule all aircraft have to do a rapid depressurisation test and an emergency descent.
Emergency descent tests are not normally carried out at VMO but at the max speed with gear extended VLE.
Speed brakes will also be extended and this will give a rate of descent of at least 8000 FPM in all the aircraft I have ever flown.
You cannot dammage the structure by rate of depressurisation.
I know of a test flight where (because of a pressurisation system snag....and the crews lack of observation ) the aircraft landed at max diff (8.55 PSID). All pressure was dumped as soon as the weight on wheels switch operated and it was white out in the cabin....interesting ground roll. The designers did not need any assesment of the structure to be carried out.
Emergency descent tests are not normally carried out at VMO but at the max speed with gear extended VLE.
Speed brakes will also be extended and this will give a rate of descent of at least 8000 FPM in all the aircraft I have ever flown.
You cannot dammage the structure by rate of depressurisation.
I know of a test flight where (because of a pressurisation system snag....and the crews lack of observation ) the aircraft landed at max diff (8.55 PSID). All pressure was dumped as soon as the weight on wheels switch operated and it was white out in the cabin....interesting ground roll. The designers did not need any assesment of the structure to be carried out.
Similar to Rainboe, I've also had the cabin depressurise in the cruise - because of a faulty gear squat switch. The aircraft was suddenly convinced it was on the ground, and one of the results was the cabin dumped all the pressure.
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I think you wil find that windows are considered part of the structure of the aircraft, Cpt Stable. A failure of window would probably start as a crack and get progressively worse until it lost all its structural integrity, then it could blow out but this is highly unlikely. Even if a hole the size of the window opened it would not cause explosive decrompession, merely a fairly steady climb rate/rapid decompression. I would not like to be sitting near it though!
If the damage is caused by a bomb and perhaps occured near the tail area then a slow speed decent might be advisable in which case it would be done at Max gear extension/flight with gear extended speed. Speed brakes would have little effect on the tail area unless your particular type has a significant buffet with them extended. The rates of decent in this configuration are not too dissimilar to the MMO, they just feel that way!
If the damage is caused by a bomb and perhaps occured near the tail area then a slow speed decent might be advisable in which case it would be done at Max gear extension/flight with gear extended speed. Speed brakes would have little effect on the tail area unless your particular type has a significant buffet with them extended. The rates of decent in this configuration are not too dissimilar to the MMO, they just feel that way!
I think that 30 seconds would be quite a long time to stay compos mentis after a rapid decompression near 40,000'. I have heard 10-20 seconds is a pretty good average. You may stay awake for a little longer but you won't be able to do anything...
That's probably why the drills start with OXYGEN MASKS ON!
That's probably why the drills start with OXYGEN MASKS ON!
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FullWings:
That's probably why the drills start with OXYGEN MASKS ON!
and the SLF are told that in the event of a loss of cabin pressure, that: "mask like these (shows mask) will appear from a panel above your head - fit your own mask before helping others"
At a now long gone UK airline, we had a brand spanking newly delivered 757 that had not had the bulk cargo door seal trimmed correctly - twice in a row, it popped out of place leading to a rapid decompression - rubber jungle - fog in cabin - a couple of SLF with bleeding ears - and a full seat cover change!
Paul
That's probably why the drills start with OXYGEN MASKS ON!
and the SLF are told that in the event of a loss of cabin pressure, that: "mask like these (shows mask) will appear from a panel above your head - fit your own mask before helping others"
At a now long gone UK airline, we had a brand spanking newly delivered 757 that had not had the bulk cargo door seal trimmed correctly - twice in a row, it popped out of place leading to a rapid decompression - rubber jungle - fog in cabin - a couple of SLF with bleeding ears - and a full seat cover change!
Paul
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What speed to use???In the olden days the industry only 'used' the high speed descent..About M83 in the DC8 and B707(Boeing advocated the use of Banking to 45 to expedite the nose drop through the Horizon with poss 'G'..
Thence the indisrty ,about the time of Aloha'questioned the 'High' speed in all cases.So the general dictum went out to evaluate before diving.With a sudden Immediate depression one was to suspect structural failure and check the Doors indication for the assessment-If strucural ,slow down or at least use the present speed,to avoid ascerbating the problem..Slow with gear down produced nearly the same rate 6000+
With the 'alt warning horn'this was a subtle failure and the cabin was above 10000',try to recontrol it,if no joy,start down fast to'MEET' the cabin alt,thence level off at the 'new' cruise alt..If your lucky no masks will deploy and you've lots of Supplemental available..
Food for thought,when your doing your A/p selections..
Cheers
On the A320 it was quite a \'slow\' affair starting down
Thence the indisrty ,about the time of Aloha'questioned the 'High' speed in all cases.So the general dictum went out to evaluate before diving.With a sudden Immediate depression one was to suspect structural failure and check the Doors indication for the assessment-If strucural ,slow down or at least use the present speed,to avoid ascerbating the problem..Slow with gear down produced nearly the same rate 6000+
With the 'alt warning horn'this was a subtle failure and the cabin was above 10000',try to recontrol it,if no joy,start down fast to'MEET' the cabin alt,thence level off at the 'new' cruise alt..If your lucky no masks will deploy and you've lots of Supplemental available..
Food for thought,when your doing your A/p selections..
Cheers
On the A320 it was quite a \'slow\' affair starting down
