Concorde depressurisation

[4Greens]

Have been trying without any success to find out how the Concorde could be certified to fly as high as it does without ,for instance, pressure suits for the pilots. Most subsonic jets are altitude limited for this very reason.

Perhaps somone could help me or was it a fiddle?

[woodpecker]

Concorde pilots have pressure breathing apparatus

[Notso Fantastic]

<Most subsonic jets are altitude limited for this very reason.>

Are you sure? Please explain. I think you will find most subsonic jets are altitude limited by:
Engine performance
Wing design area
Optimising range against performance.

Wherever did you get that statement?

[NigelOnDraft]

Ever wondered why it has small windows??

Just a clue....

[Phoenix_X]

Nigel, I don't see what you mean by that statement. I think it's clear by 4Greens' question he knows the differential px is high.

He's just wondering how it's allowed.... woodpecker answered that.

Now the thing here is, px breathing is great if you can get the mask on. On a sudden decompression on that altitude you have only a couple of seconds, a little more if you don't smoke. The decompression will create such a sudden huge differential px on the pilots, that it seems unlikely they will get themselves together, orientated and masks on in time.

Cessna has an auto-turn auto-descent for this very reason on their latest bizzjets.

[oxford blue]

I don't think that it is that unlikely, provided that the procedures are practiced. Flying at great altitude is not new. The military were regualrly doing it in the 50s and the 60s. The Venom could get up to fifty plus and the Vulcan often flew well above fifty thousand. The crews were required to train to cope with an explosive decompression by pressure breathing and were required to regularly refresh. It is true that the time of useful consciouness is small without pressure breathing and it's also true that military crews, when they flew at that altitude, kept their masks on, even though the cabin was pressurised.

I think that it's possible provided that you practice finding and fitting the mask in a hurry.

[NineEighteen]

How long would it take Concorde to descend to under 10,000ft? Can it do it in 4 mins? 12,500ft/min? Isn't four minutes the regulation time?

[TopBunk]

9-18

Spoke with a ccde flt eng a few years ago who had experienced a double engine surge. If I recall properly, the procedure required a Mach 2 descent, and he saw -34,000 fpm on the VSI!

[LEM]

What he meant was he calculated 34000ft/min descent rate.
Have you ever seen a VSI with a scale greater than 6000?

Anyway, 4Grenn's question was about pressure suits, not pressure breathing apparatus, which every aircraft has.
Don't know exactly at what altitude pressure suits become necessary in order to avoid bubbles, but the short answer is that pressure suits are not required on the Concorde (they would be required for the passengers too...) because the certification requirements take into account the loss of one small window, an immediate descent at an amazing rate and oxygen masks for breathing.
No pressure suits needed (that would be unthinkable on an airliner)

[Brit312]

Just a couple of points on this subject:-

1) Concorde like all other aircraft has to proove it can descend to a safe altitude (14,000 ft if I remember correctly ) in the required time.

2) From supersonic it's rates are not that great initially as it first has to partly slow down before it descends. Once below 30,000ft and below a certain speed, it can use it's two inboard reversers in reverse idle thrust, and then the rate of descents can become quite high ie somewhat greater than 10,000ft /min, but 34,000ft/min he must have been kidding you. Oh yes the altimeter is calibrated at least up to 10,000 ft/min

3) Concorde flight crew have all got "Pressure Breathing" at their individual stations, which is supplied via a quick donning mask. Every so often (two year intervals ? ) the crew have to
practise donning the mask in the required time and using the pressure breathing, albeit at a reduced pressure to what they would get in flight. This is monitored by a Doctor as the proceedure is somewhat dangerous. Makes you go red and puts your blood pressure up. No other type of civilian aircraft has this system, but they do have 100% oxygen systems

Regards

:O

[Bellerophon]

LEM

...the certification requirements take into account the loss of one small window, an immediate descent at an amazing rate and oxygen masks for breathing...

As you say, certification takes account of a rapid depressurisation, not an instantaneous one, and requires the flight crew to don pressure breathing masks immediately, and then, if the F/E cannot control the cabin altitude, accomplish an emergency descent.

If I may just add one or two comments to what you have posted, the passenger windows fitted in the production aircraft are smaller than the passenger windows in the prototype aircraft, a change made during certification and test flying to ensure that the aircraft met all the relevant decompression standards.

One advantage of Concorde is that with a normal cabin differential pressure of 10.7 psi, the cabin altitude is a lot lower at any given aircraft altitude than on conventional subsonic jet aircraft.

The flight crew do not routinely wear O2 masks at any stage of the flight but do have a genuine pressure breathing system available, to ensure sufficient O2 intake in the event of high cabin altitudes being attained. If required, they could get the aircraft down from FL600 very quickly.

...not pressure breathing apparatus, which every aircraft has..

I personally don’t know of another civilian aircraft that has a similar flight crew pressure breathing system to the one fitted on Concorde.

Those who have used both “Demand” and “Pressure” breathing systems know the difference between them. Those that haven’t will learn it as soon as they take their first breath wearing a real “Pressure” breathing system!

...Have you ever seen a VSI with a scale greater than 6000?...

On Concorde, once the needle indicates ±6,000 fpm on the conventional scale, a digital indication in a lower or upper window then takes over.

The VSI can thus read over a range from +10,000 fpm to -30,000 fpm, which is usually enough for our needs!


TopBunk

…Spoke with a ccde flt eng…and he saw -34,000 fpm on the VSI!...

A good story, but the Mach 2.0 surge procedure, whilst certainly very interesting, won’t produce as high a rate of descent as the Emergency Descent procedure will, and neither procedure would produce anything like 34,000 fpm.

Regards

Bellerophon

[alatriste]

I would like to check if it´s true that the MAX. CERTIFIED FL for a certain aircraft is limited by pressurization requirements, as max allowed cabin altitude for a PAX airplane is 8.000 feet. Therefor if for structural reason max differential pressure is 7.77 psi, you cannot climb above certain FL mantaining 8.000 feet cab alt., regardless of your weight.
Anything to do with oxigen pressurized system in case of depressurization?

[GlueBall]

For comparisons: The Cessna Citation X is certified to FL 510 with a cabin differential pressure of 9.3.

[4Greens]

The military situation is somewhat different as masks are on all the time. In addition at around 50,000 feet pressure waistcoats were required. Full pressure suits from around 60.000 on.

Still baffled!

[LEM]

Bellerophon,
Those who have used both “Demand” and “Pressure” breathing systems know the difference between them. Those that haven’t will learn it as soon as they take their first breath wearing a real “Pressure” breathing system!

I must miss something here. The quick donning masks you can find on a 737 or A320 are "demand" but can be regulated to Normal, 100% or Emergency (emergency being positive pressure regardless of demand).
What's the difference with the Concorde apparatus?

Regarding the VSI, it seems to me that the VSI installed is the same liquid crystal type you can find on an ATR42 or non-EFIS 737.
On this picture http://www.airliners.net/open.file/094078/M/ I can't find the digital reading you are talking about.
Surely you can enlighten me.
Thanks! :confused:

[NW1]

The LCD VSI was fitted to provide a TCAS display. It does display VS information but only +/- 6000fpm. The original VSI is a strip instrument to the right of the ADI and when the pointer hits full scale on the strip at +/- 6000fpm, there is a yellow digital display which reads to 10,000fpm on the up stop and 30,000fpm on the down stop, as Bellerophon quite rightly pointed out. Here's a better picture:http://bedsidemanor.users.btopenworld.com/images/CruiseFDShot.jpg

[TopBunk]

Bellerphon

I bow to your superior knowledge. My memory may be out a bit, the conversation was over 12 years ago, but I recalled him mentioning a very large rate of descent displayed numerically in a window below the normal VSI, as you say.

[NigelOnDraft]

<<I must miss something here. The quick donning masks you can find on a 737 or A320 are "demand" but can be regulated to Normal, 100% or Emergency (emergency being positive pressure regardless of demand).
What's the difference with the Concorde apparatus>>

Presume like the things RAF guys tried at N Luffenham in Aircraft that went 45'K+. It is nothing like the A320 "positive pressure" that blows a little 02 at you... These things positively "inflate" you at the pressure required to absorb the O2, and it takes all your concentration (and effort) to "blow out", ready for it to make your next breath.

And not really worth trying to "talk" in this process - get on with descending!

NoD

[wingtip777]

NATSO FANTASTIC could you explain why the jets are limited by :Wing design area
Optimising range against performance.
thanks

[Hot Rod]

Interesting thread, how high can you fly with the Concorde?

[brockenspectre]

::donning cloak of paranoia:: with so few days left until Concorde ceases scheduled operations, doesn't it seem a little curious to have such a thread? unless, of course, someone is planning the ultimate spectacular GB aviation/terrorism incident ??

::removing cloak of paranoia::

sorry to those who have seriously discussed this issue but ... in times of heightened alerts in GB surely we need to be a little cautious in how we offer information on these freely available public forums?

:ok:

[LEM]

NW1, thank you now I see the small label FT/MINx1ooo.

Breathing apparatus: I wonder why such a high pressure is needed :confused:

brockenspectre, do you think terrorists need our help to do it again?
I'm surprised they didn't so far.
Easy to do that anytime.
All the security measures in place are bulls**t!
An airliner today is perhaps the last small village with no law enforcement. That's pathetic.
Only ELAL is really safe. Real police on board.

:yuk: :yuk:

[4Greens]

How the Concorde getting originally certified can be a security issue is beyond me.

I can only assume no one knows the reason.

I remain still baffled.

[Pub User]

LEM

As I recall from training, the pressure is required to ensure absorbtion of oxygen within the lungs. This process (at molecular level) requires a certain pressure differential, which is not present when decompressed beyond something like FL450.

Perhaps someone who has been through AvMed training more recently than 1986 can expand a bit?

[palgia]

We talked about the crew, but what about the pax?
I don't think they have pressure breathing equipment... so whether its an oxygen candle or stored gasseous oxygen I don't understand how, in the even of a rapid decompression, the pax are supposed to be able to put on the mask and be able to absorb enough oxygen using that cheap plastic mask before losing conciousness.
Can anyone enlighten me on this?

Also consider that while the crew is regularly trained on rapid decompression procedure, many passengers never put on an oxygen mask. I have never flown on the concorde but I wonder if the pax briefing is any different that regular airlines, or if the cabin crew stresses the importance of putting the mask immediately (within 2 sec).

[LEM]

I wonder what is the exact scenario the certification people take into consideration: the loss of bleed air, the rupture of the outflow valve, or the loss of a cabin window?
If it is the latter, maybe they assume that the hole is small enough to allow engine bleed air to compensate in part for the air which escapes from the window (assuming the outflow valve will immediately close as well). Maybe the decompression under these conditions is gradual and not as violent as we might think: if it were the case, most passengers would pass over...

Also I wonder if thew crew is allowed to go to the toilet during cruise...


ps: to answer Hot Rod's question, anybody can tell what is the highest altitude ever reached by Concorde? :oh:

[Kerosene Kraut]

Think it still is 68K.