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Pax oxygen

Old 28th Jun 2007, 07:16
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Smile Pax oxygen

Hello gentelmans:
When you crz at FL350 then suddenly you find pax oxygen pressure drop to 0,what will you do ?are you going to divert or....?
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Old 28th Jun 2007, 07:52
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Same question, but crew oxygen drop to 0?
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Old 28th Jun 2007, 07:52
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there's something in jar ops that say's the first half hour of a flight below 25000' can be made without pax oxygen. because you can be at 10000' before they start being really hypoxic. so i think the right decsion would be to at least descend to fl 250 and prepare a diversion if you've still got a long flight ahead.

i won't be able to find the reference though

seb
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Old 28th Jun 2007, 07:53
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Re No Passenger Oxygen:

I guessing the regulations of most countries would allow you to continue flight if you descend to FL250 or below.

However the difficulties of continuing a flight at that level (like distance to destination, fuel remaining, safety heights, airspace restrictions etc.) may necessitate a landing nearby and some replanning.
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Old 28th Jun 2007, 09:59
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fish Pax Oxy dropping to Zero.... can't happen

pax oxy comes from a chemical reaction in those containers. there is no pax oxygen-pressure that could drop to zero because this is a totally different system. there is no oxygen-container. and no gauge. and no oxygen until someone pulls a mask. a string attached pulls/triggers an igniter pin which then burns some king of candle. in this reaction oxygen is set free. no kidding.
see: i read it on wiki, it must be true
crew oxy: classic system with a bottle containing oxy and YES! a gauge that theoretically could drop to zero. gotta be a reeeally nerdy TRE to make up that scenario of crew-oxy SUDDENLY dropping to zero in the middle of a flight. and without crew-oxy u gotta descend. maybe u can spend 30min in FL120, then it's down to FL100.

Last edited by FCS Explorer; 28th Jun 2007 at 10:00. Reason: spelling
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Old 28th Jun 2007, 10:05
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It is in JAR-OPS 1.770.

Edit: FCS Explorer, for a large percentage of commercial aeroplanes your statement is correct, but many types in use have a central oxygen system installed which is fed from cylinders of liquid oxygen. So Wiki is not always correct (or complete I should say)!
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Old 28th Jun 2007, 10:18
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I am prepared to be corrected, as always, but in over 30 years mending aircraft I have yet to meet a COMMERCIAL aircraft using Liquid O2, Mil yes but not civil.
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Old 28th Jun 2007, 10:28
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well, from "passenger oxygen" i assumed we are talking about today's commercial airliners, preferably western built As&Bs.
yet i wouldn't be surprised if some russian types had an oxy system with tanks and pipes all over the plane.
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Old 28th Jun 2007, 10:46
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Don't assume all types have individual seat row O2 cannisters. Several have plumbed in oxygen systems for pax O2 (all 747s for a start). If indications fell to zero, I would think descent to FL250 would be advisable, but if it was crew O2, why not test it over a long period by one person breathing O2 and seeing how it supplied demand? Periodic test selections supplies prerssure O2? It may be the gauge.
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Old 28th Jun 2007, 11:54
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If there is no AFM/QRH procedure then have a look in the MEL/DDPM. Probably talks about not above FL250 and ensure portable oxy for 10% of pax. So down to FL250 and look at your fuel would be my thoughts.
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Old 28th Jun 2007, 23:59
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Cool

Thank you guys,Yes,it was a 744 with piped pax and crew oxygen system,crew pressure was normal ,they are from different bottles.
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Old 29th Jun 2007, 00:41
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the 737 jurassic has O2 bottles for the passengers, the classics changed that to chemical oxygen generators.
If I saw the pax o2 gauge indicating 0 I would probably descend to FL250 or 240 after confirming that indication is real (if I can).

If I saw the CREW oxy pressure indicating 0 I would try by all means to confirm validity of that indication, for example by checking any CBs and putting the masks on and breathing for a while. if I can breathe I d probably descend a few thousand feet just in case and keep going....if I cant breathe or I got reasons to suspect the indication is real Id probably try to terminate the flight asap, that means Vmo -5 kt to destination (wx and fuel permitting) or a diversion/turnback. This is because crew O2 is not only a need during a depressurization but also during a smoke situation, so if I got no O2 that d be a bad day.
THE 737-500 MEL says the CREW O2 pressure indicator may be inop as long as o2 bottle pressure is checked and above min requirements prior to every takeoff so if a diversion or turnback is made the flight can be continued after applying the appropriate dispatch deviation procedure.
One more thing. I believe the instrument uses DC power, just by looking at what it does when you remove power, so if its reading 0, it could have failed. Id probably reset the CB once or twice too.
REgards,
SW.
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Old 29th Jun 2007, 02:04
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Our Airbuses also only have gaseous oxygen systems for both crew and pax therefore have pressure guages for both.
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Old 29th Jun 2007, 02:36
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Let me try to add some commen sense to this discussion:

1. The air (oxygen) the passengers breath on all current airliners comes for outside the aircraft. It enters the passenger cabin through the engines as bleed air. From the engines goes through a series of coolers and heaters that provides the passengers with breathing air, heating air, air conditioning and cabin pressurization. Even if all the engines fail, as long as the engines turning, you will still have air to breath and pressurization, even though the heat and air condition systems may be lost. So there is no way for the passengers to run out of oxygen.
2. There is a second source of air (oxygen) which is only used in emergancy, like when there is rapid decompression or a failure in the bleed air system and the cabin pressure can not be controled. There are two types of these systems. The hard plumbed system, were oxygen lines are ran from central tanks to individual masks for the passengers and crew. Or chemical oxygen gererators which are provided for each passenger seat, in the lavs and for the cabin crew.
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Old 29th Jun 2007, 07:26
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You call that common sense? What's the rest of the discussion been?

Should you have an explosive decompression, even with all engines (and packs) pumping out maximum air supply, you only have a very limited time of consciousness. Therefore you need to rapidly resort to emergency oxygen supplies which comes from your emergency system.....and the gauge is reading zero. Whaddya gonna do? That is what the discussion was about.

Thank you for your 'common sense' and explaining the technicalities, but you are way behind and haven't answered the question!
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