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B787 O2 supply

Old 6th Nov 2019, 17:37
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Originally Posted by Flight Alloy
Here is a link to the original STORY . . .
Thanks for the link!

Last edited by OldnGrounded; 6th Nov 2019 at 19:55.
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Old 6th Nov 2019, 19:44
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I thought there were more drop down passenger masks than seats, to allow for infants sitting on laps
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Old 6th Nov 2019, 19:52
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Originally Posted by ATC Watcher
there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
These people are not walking along at sea-level (or whatever the cabin altitude is at the time of the depressurisation) one second, and the next they are at 39,000 feet. They spend many weeks and sometimes months acclimatising, where the number of red cells in their blood gradually increases to a level where the amount of oxygen scavenged from the atmosphere is greatly increased.

Even then, survival at that altitude is only for a matter of hours even with supplementary oxygen, which is why it’s called the ‘death zone’
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Old 6th Nov 2019, 20:12
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Originally Posted by ATC Watcher
there are lots of people that climb the Himalayas without oxygen
I was interested in the definition of Ďlotsí being used here so I turned to Google and found this which quotes the all-time number of Everest summits without oxygen as 200 of the 5000 total ascents. So, an elite within an elite, who donít just acclimatise for months: they train for years to reach that level of fitness, and probably self-select for some kind of genetic advantage too. Less than a planeload *ever* out of the thousands of planeloads that fly *daily*. Interesting use of Ďlotsí indeed! Even widening the net to include all those who climb from base camp to the oxygen-donning altitude, the numbers involved are still a drop in the ocean on the global statistical scale of the airline industry.
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Old 6th Nov 2019, 21:58
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My previous post was done tongue in cheek. I do know what happens with a sudden decompression and the max ROD. A significant proportion of paxs would die. Others would have long term hypoxic effects - dont worry about the medicine, just be assured any good lawyer would be after $$$ £££s for loss of job attainment, failure of relationships, mood swings and potential early cognitive degeneration

Luckily I normally fly below 2000 feet so I am not effected but I am surprised at the laisse faire attitude to yet another Boeing issue. The fact that nobody has come to harm is a matter of luck not judgement. Surely this should be an issue to be sorted immediately with interim measures such as free standing oxygen??? If it had been cc oxygen......
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Old 6th Nov 2019, 23:48
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Originally Posted by topgas
I thought there were more drop down passenger masks than seats, to allow for infants sitting on laps
I was going to ask about this. Presumably there is some over-provision to allow for failures: does it get near to 25% (assuming that figure for failures is true/typical)? I'd also like to ask if this is a Boeing problem, or more widespread (assuming this equipment is supplied by a third party).
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Old 6th Nov 2019, 23:56
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Originally Posted by FlightlessParrot
I was going to ask about this. Presumably there is some over-provision to allow for failures: does it get near to 25% (assuming that figure for failures is true/typical)? I'd also like to ask if this is a Boeing problem, or more widespread (assuming this equipment is supplied by a third party).
The FAA, being data-driven, came to the same conclusion: there is four masks per row of three, plus a couple extra in the toilet, so if 25% don't work everyone should still have a working mask, statistically speaking. Really don't see what the problem you people have.





Oh, the whole row wouldn't work if the valve doesn't open....
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Old 7th Nov 2019, 00:29
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Originally Posted by Lake1952
I would prefer that my cockpit crew test their oxygen supply to assure it works.
At my airline a functional check of all cockpit masks is required on the first flight of the crew day (i.e. not repeated at each turnaround). While the check is conducted "in container" i.e. the mask is not actually removed and donned, I have full confidence in the check other than it confirming that the gas being delivered is actually O2. I have to rely on ground servicing integrity for that.
To answer another poster's query, an additional pax mask is installed above every set of seats.

Regarding failure to use supplemental O2 in the case of depressurisation I'm going to go out on a limb and say that during even the worst case scenario, i.e. explosive depress at FL450 followed by a poorly flown emergency descent to an intermediate altitude due terrain followed by a further descent to 10000' within 30 minutes of initial depress, the risk of serious or lasting effects is very low except, perhaps, for physical injury due to unrestrained pax movements while unconscious, or rarer cases where an underlying medical condition is triggered by the resulting hypoxia.

My rationale:
While Time of Useful Consciousness at FL450 is quoted as 9-15 seconds (it may be less in affected people, think seriously unfit or heavy smokers) and is reduced by activity, think walking back to your seat, the time to actual unconsciousness is much longer. And the time to actual deleterious effects of hypoxia on brain or other cells is even longer still.
There are reports of passengers failing to refusing to don masks with no long-term or serious after-effects provided that the cabin altitude was reduced in the previously mentioned timely manner.

Now, I am not defending the position challenged by the OP. Safety-sensitive systems such as supplemental O2 systems should not be experiencing 25% failure rates and manufacturers and regulators should not be brushing aside genuine reports of such failures. O2 systems are installed for very good reasons but I get the feeling we are overstating the risk a little.

Ok, let the howling begin....
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Old 7th Nov 2019, 03:11
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Originally Posted by Flight Alloy
Nope, 787 uses O2 bottles both for flight deck and cabin oxygen systems. Each 3 seat group shares one oxygen bottle in the bulkhead overhead, fired by a pyrotechnic valve when operated. These valves, by definition single use, can not be tested, and are the source of failures.
I wonder what the failure mode of the valve is. Open circuit in the squib (electric match)? Bad or weak pyrotechnic charge?

The squib circuit should be testable for continuity non-destructively. It's what demolition pyrotechnicians do prior to setting off a group of charges to bring a building down. The failure of some could result in the structure falling in an uncontrolled manner. I would be seriously surprised if the O2 system did not incorporate such a built-in-test (BITE).

Pyrotechnics themselves are pretty reliable, assuming that they are built with some quality control in mind. And if a suitable level of reliability can't be achieved, either redundant charges or a manual backup to open the O2 valve might be needed.
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Old 7th Nov 2019, 05:23
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@ Speed of sound + @ easy Street :
They spend many weeks and sometimes months acclimatising, where the number of red cells in their blood gradually increases to a level where the amount of oxygen scavenged from the atmosphere is greatly increased.
Good point . Agree . My point was about permanent brain damage and even death for being subject to single minutes of O2 deprivation. But you are right . Point taken.
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Old 7th Nov 2019, 08:19
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While Time of Useful Consciousness at FL450 is quoted as 9-15 seconds
In the event of a sudden decompression itís closer to 5 seconds. You canít hold your breath and your lungs will work in the opposite sense and dump oxygen from your blood to atmosphere.

If you can get to a breathable altitude within 90 seconds youíre probably going to be OK. The problem is that if someone has stopped breathing or suffered cardiac arrest from hypoxia, then theyíre unlikely to spontaneously recover going below 20,000ft.
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Old 7th Nov 2019, 08:41
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I find this demonstration of a decompression at FL450 interesting and alarming.

Count how long it takes the prepared gentleman to lose consciousness.


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Old 7th Nov 2019, 13:19
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Originally Posted by 2bigmellons
I find this demonstration of a decompression at FL450 interesting and alarming.

Count how long it takes the prepared gentleman to lose consciousness.
SNIP VIDEO
At height say above 35,000 ft as the emergency oxygen masks are not pressurized they will not prevent loss of consciousness. However, the availability of higher percentage oxygen in the low pressure air being breathed means that the pax wearing masks will come round faster when back to 10,000ft and have less chance of brain damage. This is why an emergency descent to 10,000ft is required. Do not expect anyone in the cabin to be reliably responsive above that altitude.
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Old 7th Nov 2019, 16:04
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Any idea why Boeing have gone for O2 cylinders rather than chemical generators? Space/weight/maintenance/cost?
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Old 7th Nov 2019, 16:48
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Originally Posted by ATC Watcher
Not a medic but I think the critical part is from 400 to 300 , at 4000 ft/min (typical emergency descent on most types) say 2- 3 min deprivation ; like a long underwater scuba dive ., brain damage ?
But from 30.000ft you get back a bit of oxygen , there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
But again I am not a brain specialist..
I just remember a decompression on a Spantax DC8 over the Netherlands from FL33 or 370 where half the O2 masks did bot deploy because stuck by nicotine tar .. Diverted to AMS. .. Nobody was injured, shocked yes, but most of the pax continued a few hours later to the Canaries...

4000í per minute ? You ainít even trying . 7500í is achievable
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Old 7th Nov 2019, 16:55
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Originally Posted by deltahotel
Any idea why Boeing have gone for O2 cylinders rather than chemical generators? Space/weight/maintenance/cost?
For the 787 the answer is invariably, "to save weight". However, there are other considerations such as the difficulty in transporting O2 generators after the Valuejet tragedy.

Regarding BITE checks, from memory I think there's an LED indicator on each bottle/valve assembly that shows the go/nogo state of the unit. I think they are ' on demand' too which means less O2 is required and therefore a smaller bottle, which again saves weight.
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Old 7th Nov 2019, 17:12
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Originally Posted by Meester proach
4000í per minute ? You ainít even trying . 7500í is achievable
At VMO, gear extended and in a side slip, maybe. So definitely not realistic in the real life. 4000 is a correct figure.
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Old 7th Nov 2019, 18:28
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"At height say above 35,000 ft as the emergency oxygen masks are not pressurized they will not prevent loss of consciousness."
How are the flightdeck masks pressurised? ( Not a professional, but thinking that "pressurised" does not, in this sense, refer to oxygen pressure at the mask.)
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Old 7th Nov 2019, 19:11
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Flight deck masks can give air mix or 100% and they can also give over pressure - main use for smoke/fumes so the smoke can’t get into the mask but will also give an element of pressure to assist O2 uptake. Flight deck would be ok for a good length of time purely from an O2 perspective.

Pax masks don’t really seal so it’s only ever going to be O2/airmix at lowish pressure.

At 35000’ it’s minus lots - prob -50. Any time spent above 25000 gives a good chance of decompression sickness (sub aqua experts anyone? Bends chokes creeps staggers).

All the the above says get lower quickly. The 757 (Mr Boeing’s original streamlined crowbar) will do 6000fpm at Vmo, but if it’s a rapid decompress with the probability of structural damage do you really want to descend at Vmo?

Just some thoughts. Slightly easier as a freight pilot as everyone on board will be on the flight deck with proper masks and O2. Much harder with pax from 0 to very old, all of unknown health and no knowledge or training.



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Old 7th Nov 2019, 19:56
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Originally Posted by deltahotel
Flight deck masks can give air mix or 100% and they can also give over pressure - main use for smoke/fumes so the smoke canít get into the mask but will also give an element of pressure to assist O2 uptake. Flight deck would be ok for a good length of time purely from an O2 perspective.

Pax masks donít really seal so itís only ever going to be O2/airmix at lowish pressure.

At 35000í itís minus lots - prob -50. Any time spent above 25000 gives a good chance of decompression sickness (sub aqua experts anyone? Bends chokes creeps staggers).

All the the above says get lower quickly. The 757 (Mr Boeingís original streamlined crowbar) will do 6000fpm at Vmo, but if itís a rapid decompress with the probability of structural damage do you really want to descend at Vmo?

Just some thoughts. Slightly easier as a freight pilot as everyone on board will be on the flight deck with proper masks and O2. Much harder with pax from 0 to very old, all of unknown health and no knowledge or training.



No mask can work as a 'pressurized' mask, aka delivering more pressure to the lungs than ambient, as without a pressure suit, the lungs and their muscles have very little capacity to breathe/pump air, as they fight to deflate the lungs with every breath against the oncoming pressure (imagine a balloon and trying to deflate it against pumping). With this limited muscle 'overcapacity', pressurized breathing is only possible with suits that also pressurize the chest area to the same pressure as the breathed gas.
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