O2 question

[slim75]

Hi, an ineresting question i've come across that i'm not sure what the correct answer would be. Please provide assistance if able.
-On a long range overwater flight 5 hours from your destination, the passenger O2 masks drop from their compartments with no cockpit indications of a loss in pressurization. Do you divert or continue to your destination? what has caused the masks to deploy? Is this deployment due to a pressurization leak?

thank you in advance for your thoughts.

Regards,

Slim

[EW73]

You would have to have missed both the cabin altitude warning, at 10,000 feet cabin, and the Master Caution that occurred when the PASS OXY overhead indicator illuminated as the masks dropped.
Whether the cabin masks were deployed manually or automatically (at 14,000 feet cabin), the PASS OXY light will illuminate.
There is no other way to deploy the cabin masks...

As far as your question to divert is concerned, for me it would depend on whether the passenger oxygen system is actually pressurized breathing oxy or generated from chemical oxygen generators.
If they were oxy generators, I think I would divert, as a safety concern, as the generators cannot be turned off after initilized, whereas the pressurized oxy can, and be retained for possible use for the remainder of the flight.
This is, of course, the Boeing system.

[isaneng]

I suspect this may be too vague a question for a complete answer, due to aircraft system differences. I have flown aircraft with systems that could be isolated in flight from the flight deck (and, perhaps more importantly, reinstated), and others where a trip downstairs would be required. If the rubber jungle dropped on unwary passengers, most would now be very upset, depite PA announcements. Have you now got an oxy rich environment in the cabin? Did the 7 pax that listened to the brief initiate oxy flow from their masks.... Too many variables I suspect.

[GlueBall]

In most configurations dropped masks will nor dispense O2 until they are pulled.

[Self Loading Freight]

There's also the question that if the rubber jungle has deployed in error, what happens if it's later needed in earnest? If nothing else, there are problems with the system designed to keep us fat'n'happy above 10000', so it's time to go downstairs.

[Pub User]

If the masks drop, some of the passengers will (quite rightly) pull them and put them on, thus you no longer have a fully operational passenger oxygen system.

EU Ops:

(iv) Aeroplanes intended to be operated at pressure altitudes above 25 000 ft or which, if operated at or below 25 000 ft, cannot descend safely within four minutes to 13 000 ft, and for which the individual certificate of airworthiness was first issued on or after 9 November 1998, shall be provided with automatically deployable oxygen equipment immediately available to each occupant, wherever seated. The total number of dispensing units and outlets shall exceed the number of seats by at least 10 %. The extra units are to be evenly distributed throughout the cabin.

If you can get get to your destination at FL250, then I think you could satisfy the regulation, otherwise you'd have to divert.

[Escape Path]

A couple of stupid questions:

1. How long will the activated oxy masks supply oxy?
2. Do the inactivated masks will work if needed afterwards?

A somewhat stupid thinking of mine goes like this: If the inactivated masks can be used later then one would be able to continue at cruise altitude and if something that needs the use of them happens, then the oxy is there. As for the activated masks, you'd still have the 10% surplus of oxy masks which may be used in place, provided not too many pax activate their masks. That way you wouldn't need to divert or to descend to 250, possibly forcing to divert as well.

Bear with me please

[isaneng]

Activated masks will supply O2 until either reset at individual unit (are your cabin staff trained to do this?) or supply turned off at central point. Until then they are leaking 100% O2 into the cabin. Are you really going to go and count the deployed masks? Does that even have a point, as if deployed they are still available for use, surely? If resetting individual masks at their units, why not restow? Quite frankly, whilst theoretically possible, it all seems exactly that - theoretical. With a load of worried passengers, a diversion seems sensible.

[Escape Path]

@isaneng

Thanks for the reply to my question. The reason I asked is because I fly the Twin Otter, which is neither pressurized nor does it have cabin crew, and while I'm familiar with the oxygen regulation, it's a bit rusty since I don't use it on a fair basis.

Regards

[slim75]

Thanks for the thoughts on this question and scenerio. I know more from asking.

Regards,

Slim

[SuperflyTNT]

What are the O2 requirements for commercial a/c ? When does the PIC deem necessary to don oxygen masks and drop the oxygen masks for the passengers? I'm aware that in the event of cabin decompression is one.



I haven't been able to find the ICAO annex for oxygen requirement for commercial a/c.

I found the ICAO annex part ii and iii but it states that they are for any purpose other than public transport. States that - between FL100 and FL130 if flight shall last for more than 30mins all crew must don O2 masks and above FL130 they are recommended to use oxygen at all times.