TheSonntag From Germany, joined Jun 2005, 4328 posts, RR: 29 Posted (9 years 10 months 2 weeks 6 days 11 hours ago) and read 10425 times:
Fortunately this never happened, but what would have happened if Concorde had a rapid decompression at Mach2 and cruise level? Would this have been survivable? Which measures were taken to prevent that?
Starlionblue From Greenland, joined Feb 2004, 17380 posts, RR: 66
Reply 3, posted (9 years 10 months 2 weeks 6 days 7 hours ago) and read 10341 times:
The higher you are, the larger the pressure differential between the outside and inside.
To counteract this, the smaller the window, the less air can escape in a given amount of time. The Concorde pilots on the board can probably answer this better, but the aircraft was certified to the same standard as any other airliner, so I assume it had to be able to maintain (some) pressure even with a window "popped". It would not have been certified if decompression->automatic doom.
"There are no stupid questions, but there are a lot of inquisitive idiots."
Bellerophon From United Kingdom, joined May 2002, 586 posts, RR: 58
Reply 7, posted (9 years 10 months 2 weeks 6 days 1 hour ago) and read 10269 times:
... what would have happened if Concorde had a rapid decompression at Mach2 and cruise level?...
To answer your question, we first need to know just how rapid the rapid decompression was.
A near-instantaneous decompression at 60,000 ft would have been very serious. Passengers exposed to atmospheric pressure at that height for any appreciable length of time would have had only a few seconds of awareness followed by a merciful lapse into unconsciousness.
The sort of damage necessary to have caused this would have brought with it a whole host of other problems, and probably the aircraft would have ceased to have been a viable flying machine - the early Comet accidents being a case in point.
However, in the overwhelming majority of decompressions, experienced over many years on other aircraft types, the aircraft did not instantly depressurise to ambient atmospheric pressure, even if it may have felt like it to the occupants.
Whether due to pressurisation system failure, discharge valve failure, a small hull breach, a door or window blow-out, or just plain human error, the cabin took time to decompress, often a considerable amount of time.
It is this time, the time the cabin takes to climb which provides the flight crew with a safety margin, precious seconds in which to act to protect passengers and crew from extreme cabin altitudes.
On Concorde, this involved the crew in protecting themselves (pressurised O2 masks) analysing the situation (what warnings?, what cabin rate-of-climb?) rectifying if possible (re-instating packs, selecting alternate systems, closing errant valves manually) or, if control of the cabin had been irretrievably lost, initiating an emergency descent.
The cabin altitude on Concorde was typically around 5,000 ft in the cruise, and in common with most commercial aircraft, various flight deck warnings would occur as the cabin altitude rose through 10,000 ft, and again passing through 14,000 ft, to alert the crew to any problem, assuming their own eyes, ears, sinuses and lower intestines had not already done so!
There were also many protection devices fitted to Concorde to ensure that the cabin altitude never exceeded 14,000 ft, however, even had they all failed and the cabin had been climbing at 5,000 fpm, it would still have taken 36 seconds before the cabin altitude exceeded 8,000 ft.
It would have taken 108 seconds before it exceeded 14,000 ft and around 3 minutes for the cabin to exceed 20,000 ft, by which time the aircraft would have been well on its way down to safety in an emergency descent.
In most cases, the cabin altitude would never have got above 20,000 ft, and the overwhelming majority of these incidents, though alarming, would have been highly survivable for all occupants. The chances of passengers ever being exposed to atmospheric pressure at FL600 was an extremely remote possibility.
It never even came close to happening, during 27 years of commercial service.
TripleDelta From Croatia, joined Jul 2004, 1156 posts, RR: 6
Reply 10, posted (9 years 10 months 2 weeks 5 days 21 hours ago) and read 10190 times:
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Quoting Starlionblue (Reply 3): The higher you are, the larger the pressure differential between the outside and inside.
To counteract this, the smaller the window, the less air can escape in a given amount of time.
There's another reason as well - every window is basically a hole in the plating. Every hole reduces the local structure strength, possibly leading to a structural failure around the hole (because of the lower number of structural elements and stress distribution - what happened in the first Comet I disaster if I'm not wrong).
In a normal airliner, the pressure differential at its cruise altitude dictates one window size. On the Concorde, the higher pressure differential requires a smaller one, since the stress it produces on the airframe is greater. Reducing the size of the window - that is, reducing the hole and the number of "missing" structural elements - would also reduce the chances of a structural failure around the window, since more structural elements are opposing the greater stress.
But I wonder: the Concorde was built with better hermetisation than an ordinary airliner - to reduce the amount of air flowing out. The engine compressors are not as effective up around FL600 as they are at FL300, which would mean a lower amount of air flowing into the cabin at lower pressure. However, how would Concorde's speed influence this? Less air flowing into the compressor (in terms of volume), but at a higher speed?
HiFi From Brazil, joined Apr 2005, 192 posts, RR: 0
Reply 14, posted (9 years 10 months 2 weeks 5 days 18 hours ago) and read 10108 times:
Quoting Starlionblue (Reply 3): It would not have been certified if decompression->automatic doom.
The concorde probably wouldn't be certified by nowadays safety standards.
In case of a cabin decompression, an airliner must be able to descend to 25000 ft in less than 2min (unless decompression is very slow):
(a) Pressurized cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude of the airplane under normal operating conditions.
(1) If certification for operation above 25,000 feet is requested, the airplane must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 feet after any probable failure condition in the pressurization system.
(2) The airplane must be designed so that occupants will not be exposed to a cabin pressure altitude that exceeds the following after decompression from any failure condition not shown to be extremely improbable:
(i) Twenty-five thousand (25,000) feet for more than 2 minutes; or
(ii) Forty thousand (40,000) feet for any duration.
(3) Fuselage structure, engine and system failures are to be considered in evaluating the cabin decompression."
In case it could not be proven that the Concorde was able to make an emergency descent from FL600 to FL250 in less than 2min (Bellerophon, could the concorde make it?), they would have to PROVE that decompression is extremely improbable, meaning that its probability of occurence is inferior to 10e-9. That's not at all easy to do, not even for sudden decompression.
In fact, for the Concorde, item (a)(2)(ii) means that sudden decompression must be extremely improbable from the start.
And cabin decompression isn't the only issue that would jeopardize an updated concorde certification.. just think 'engine position', for example!
Vc10 From United Kingdom, joined Nov 2001, 1431 posts, RR: 15
Reply 15, posted (9 years 10 months 2 weeks 5 days 17 hours ago) and read 10092 times:
The size of Concorde's windows are such that would allow a blowout of two windows without the aircraft's pressurization being compromised severely. The reason for this is the area of two windows roughly equals the total area of the open controlling outflow valves, so if the windows went the outflow valves would close and the pressure would remain roughly equal.
Now I am not saying the crew would carry on serving the dinner if this happened as it would be noisy and dangerous for anybody near those windows, and the cabin height might climb , but not at a catastrophic rate.
Anyway I always thought the small windows were handy as there was one for each eye
Jetlagged From United Kingdom, joined Jan 2005, 2606 posts, RR: 25
Reply 18, posted (9 years 10 months 2 weeks 5 days 17 hours ago) and read 10057 times:
Quoting TripleDelta (Reply 10): The engine compressors are not as effective up around FL600 as they are at FL300, which would mean a lower amount of air flowing into the cabin at lower pressure.
You don't need high pressure air to pressurise a cabin. In fact it only needs to be just above the target cabin pressure. Part of the function of a pack is to reduce bleed air pressure to a level at which it can be used.
As far as compressor efficiency goes, they are still efficianet at FL600 in terms of pressure ratio. Also you are forgetting that in supersonic cruise, most of the compression comes from the intake. There's plenty of airflow and certainly sufficient pressure.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Wingscrubber From UK - England, joined Sep 2001, 858 posts, RR: 0
Reply 19, posted (9 years 10 months 2 weeks 5 days 17 hours ago) and read 10055 times:
The noise/shockwaves generated in a possible supersonic de-compression would probably burst eardrums and cause a variety of injuries to crew and passengers akin to those suffered when caught in a bomb blast I'd imagine...
TripleDelta From Croatia, joined Jul 2004, 1156 posts, RR: 6
Reply 20, posted (9 years 10 months 2 weeks 5 days 15 hours ago) and read 10019 times:
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Quoting Jetlagged (Reply 18): You don't need high pressure air to pressurise a cabin. In fact it only needs to be just above the target cabin pressure. Part of the function of a pack is to reduce bleed air pressure to a level at which it can be used.
Yes, you're correct, I had a conceptual error in my head
Quoting Jetlagged (Reply 18): As far as compressor efficiency goes, they are still efficianet at FL600 in terms of pressure ratio. Also you are forgetting that in supersonic cruise, most of the compression comes from the intake. There's plenty of airflow and certainly sufficient pressure.
So the pressurisation system is then much like the one on a normal airliner, right? Taking air directly from behind the intake, just before the first compressor stage would be an unnecessary complication in that case I guess, as it would only be used in the supersonic region.
GDB From United Kingdom, joined May 2001, 13465 posts, RR: 77
Reply 21, posted (9 years 10 months 2 weeks 5 days 15 hours ago) and read 10001 times:
Mirrodie, I read Mayday around 1982!
Bellerphon was a BA Concorde pilot, until October 2003, since (like me) he does not choose to have his name on here, it's not for me to bandy it around, though I worked out who it was.
He also makes valuable contributions to the forums on www.concordesst.com
I was in Engineering on the type from only 1997 to the very end.
VC-10 was on the fleet too, earlier in it's life at BA, I suspect rather more in depth too.
As has been noticed by one poster, the cabin pressure on Concorde was indeed lower that conventional airliners.
VC10 From United Kingdom, joined Nov 2001, 1431 posts, RR: 15
Reply 22, posted (9 years 10 months 2 weeks 5 days 15 hours ago) and read 9997 times:
The pressurization air source on Concorde is a bleed from the engines compressor, just like many other aircraft.
Now there is an air bleed from the top of the intake area and forward of the compressor, known as the secondary air bleed. This air source is available when the "Secondary Air Doors" open above 220 kts, however this air is used to cool the outer case of the engine during the flight, and has nothing to do with the pressurization system .
Airfoilsguy From , joined Dec 1969, posts, RR:
Reply 23, posted (9 years 10 months 2 weeks 5 days 12 hours ago) and read 9942 times:
What causes such rapid lose of consciousness at high flight levels? Shouldn't time to lose of consciousness be dictated by how long you can hold your breath? I know air would be forced out your lungs at low air pressure but shouldn't you be able to last more then a few seconds?
Its Hypoxia, its kind of like being somewhat very drunk and happy. We were always taught to look for signs in other people (as you can't detect it in yourself that much). Its the lack of oxygen that makes everyone feel very happy and eventually everyone just falls unconscious and thats it.
Luckily they never forced us into pressure chambers, so we just got to watch the US Armed Forces (not sure which area) video instead.
An intresting topic, I'm just glad we will never find out the answer for sure now, just a shame why.
Lifes a train racing towards you, now you can either run away or grab a chair & a beer and watch it come - Phil
25 David L
: I think some here don't realise how easily I can be confused - can we just clarify whether it was the cabin pressure or the cabin altitude which was
: Hehe. Just for the record, I don't think Bellerophon, GDB et.al. are posers. IMHO they are valuable contributors to the board and know what they are
: How does this logic work out.Isn't the MOFV near closed position in cruise. Were you in Concorde Mx. regds MEL
: I agree.. I'm just saying that it wouldn't meet the updated regulations.. And in that statement you quoted I was also refering to other certification
: For you who doesn't know, and his modesty to not write it, Bellerophon was flying the Concorde. Aim for the sky! Sudden
: My question is now. If that would've happened over the Atlantic half way through the journey. They made anemergency descent to a safe altitude and sto
: Well, just imagine Concorde ditching and sinking to ground the same place where Titanic hit an iceberg, with many celebrities on board... Would've be
: Right i forgot about that they're flying NAT routes. So i guess you're right. There might always be something near to land the bird. But as operation
: Hawk21M, In answer to your query [reply27 ] , the outflow valves would be at their control position during cruise which is a variable depending on Cab
: Jush, though I'm sure Bellerphon can elaborate, flight planning was based around such contingencies. But the point about modern safety standards had r
: What Delta P was the Cabin Pressurised till. regds MEL