Highest legal altitude with PAX OXY MASKS failure

[Lantirn]

As per title:

What is the maximum allowable legal altitude which an airliner can fly assuming the PAX OXY masks have failed? (obviously failed in flight, because this is a no dispatch condition)

Common failure affecting this system is AC ESS BUS fault on the A320.

If I am not mistaken some props are flying with maximum altitude limitation of 25000ft for this purpose when they are not equipped with pax masks option.

Is 25000ft applicable in that case? I guess that would not be so simple, terrain below should be a factor.

[FullWings]

I don’t know if there is a maximum legal altitude which covers all aircraft, but for each type it should be in the DDG. In mine, it allows despatch at various maximum levels up to FL250 but with restrictions, one of which being you have to be able to get to 13,000’ within four minutes of pressurisation loss anywhere along the route. Again, I don’t know whether this is type-specific or comes from some overarching regulation.

P.S. Are you doing an ATQ?

[Lantirn]

Fullwings,

Thanks for the info, I dont have any particular info in my company manuals. But will try to search on AirOps.

P.S I have no idea what ATQ means, :uhoh: I am preparing for my command course which will begin in 2 weeks.

[FullWings]

Good luck (although I don’t think you’ll need it); if you’re down to this level of minutiae then you’ve probably done more than enough. Keep the big picture in sight.

[Lantirn]

Thanks a lot, will try my best :)

[mustafagander]

In Oz to cruise above F259 there is a series of items listed in AIP (I think) which must be satisfied. Unsurprisingly one of them is pax O2.

[excrab]

When I operated a turboprop with no drop down masks the max was FL250, there were limitations regarding how quickly you had to be able to get dorm to FL120 (if I remember correctly) and you had to carry oxygen for 10 percent of the passengers, I think we carried four O2 bottles each with two
masks (on an 80 pax aircraft). These are pretty much the same requirements in the B737 MEL to allow dispatch with the passenger oxygen system unserviceable. I would have thought Airbus would have something similar in their MEL as well, otherwise the aircraft would be grounded if the system failed.

[deltahotel]

If you’re prepping for a command course, it’s probably more important to know where to find this level of detail rather than trying to remember everything about everything.

Good luck

[FullWings]

If you’re prepping for a command course, it’s probably more important to know where to find this level of detail rather than trying to remember everything about everything.
Amen. Nobody can attain this level of knowledge, nor is expected to. It’s actually counter-productive when changes occur in the background all the time.

In order of importance (IMO):

1. Recall/Memory items/drills.
2. Fuel policy in your OM A (especially the bits about when you’ve got less than you might like).
3. Everything else and where you might find out about it if you’re not sure.

You’d be surprised how many are hesitant around 1. & 2.

Oh, and

0. Be nice, and use all the CRM you have to ensure a safe, efficient, commercially minded and fun operation...

[Lantirn]

If you’re prepping for a command course, it’s probably more important to know where to find this level of detail rather than trying to remember everything about everything.

Good luck


Hi, well said and thank you.

This is a no dispatch condition (AC ESS BUS) and my OM-A states only the typical AIR-OPS table with altitudes and percentages of pax oxygen. Its not applicable in my case. You have 0% of useable masks, except if the cabin crew go and extend manually the masks on each row, a solution that I wouldnt like my crew to do in a emergency descent.

My question would require from the beginning an out of the box solution for something that its not documented, hence my post. Obviously flying at 10000 ft is a solution as per MEL but that’s for dispatch and you are already flying. ECAM doesn’t restrict you so there is room for conversation here.

I wouldnt have posted a question for something that I can find in my own manuals.

Different companies, different operations and different manuals is the reason of my post. Someone might know something that i cant find here.

[hans brinker]

Hi, well said and thank you.

This is a no dispatch condition (AC ESS BUS) and my OM-A states only the typical AIR-OPS table with altitudes and percentages of pax oxygen. Its not applicable in my case. You have 0% of useable masks, except if the cabin crew go and extend manually the masks on each row, a solution that I wouldnt like my crew to do in a emergency descent.

My question would require from the beginning an out of the box solution for something that its not documented, hence my post. Obviously flying at 10000 ft is a solution as per MEL but that’s for dispatch and you are already flying. ECAM doesn’t restrict you so there is room for conversation here.

I wouldnt have posted a question for something that I can find in my own manuals.

Different companies, different operations and different manuals is the reason of my post. Someone might know something that i cant find here.

So that is something I haven't thought about that way, and therefore a good question. I will need some time to think.

[john_tullamarine]

A quick read of 25.1447(c)

eCFR :: 14 CFR Part 25 -- Airworthiness Standards: Transport Category Airplanes (https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-25)

might be useful.

The F250 thing has been there forever and a day.

[Lantirn]

A quick read of 25.1447(c)

eCFR :: 14 CFR Part 25 -- Airworthiness Standards: Transport Category Airplanes (https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-25)

might be useful.

The F250 thing has been there forever and a day.

John that’s very useful.

What I can extract from that is, you can fly up to 30000feet in my case.

But you are not RVSM since one PFD is lost so FL280.

[sonicbum]

John that’s very useful.

What I can extract from that is, you can fly up to 30000feet in my case.

But you are not RVSM since one PFD is lost so FL280.

Hi Lantirn,

in EASA land your reference would be CAT.IDE.A.235 Supplemental oxygen – pressurised aeroplanes.

Always keep in mind that those are certification regulations that are fulfilled by the A320f. In abnormal ops you may want to refer to those regulations to mitigate the threat of a decompressions in the absence of an automatic oxygen deployment system following your failure.

[FullWings]

As Sonic shows, it’s a grey area (which you will encounter lots of in the LHS). When you transition from MEL/DDG to QRH, the former becomes informational rather than directive. Certification requirements are interesting but have the potential to lead you up the garden path in the real world.

If you were on a long overwater, or over high terrain flight at FL370 and became aware that there was a problem with the passenger oxygen system but everything else was functioning nominally, what would you do? Dive down to FL250 or below (which may not be possible in some parts of the World) and divert? Assess the likelihood of a rapid complete pressurisation failure as remote and carry on? Something between the two? The point is that there is a balance of risk between various options e.g. an NPA into a unfamiliar alternate in marginal weather carries a non-zero risk. Not to mention the disruption and ensuing problems once on the ground. Your environment on the day will have a big input into what action (if any) to take; if you can contact a Company technical manager, they would be able to talk you through options as well.

Rule-based decision making only takes you so far, and that’s why having a open and iterative process often leads to a better quality of outcome. On my type, if there was a leak, you’d eventually get a message and a checklist. The message says: “PASS OXYGEN LOW” and the checklist says: “The passenger oxygen pressure is low.” Genius! And that’s all the help you’re going to get...

[Lantirn]

Thanks both.

Didn’t want to accommodate in my post decision making on that failure (pax mask failure) in real life because the most probable action one would make would be to continue as the risk of having also a pressure issue is highly improbable unless your company wants otherwise or you have another failure that would make you believe that the risk is not worth it.

Also AS ESS BUS fault is a serious failure, and although you don’t lose much on your systems (you still have other backups) you still don’t have your PFD ND and one central screen. That maybe would justify to continue to your destination if it’s close by but when your destination is reasonable away and there is bad weather enroute I would discuss that, take every possible info from company and most probably I would try to ensure a diversion landing to an at least CAT 1 airport. Flying with half your screens is not fun at all.

Thats why I didn’t want to discuss the decision, but rather to stay technical to discuss what altitude would be a good compromise assuming you can descent without terrain at that altitude till you land.

AMC1 CAT.IDE.A.235(e)

That makes it 25000ft, thats what I understand from this document

[john_tullamarine]

Certification requirements are interesting but have the potential to lead you up the garden path in the real world.

Potentially an awkward view, methinks. "Interesting" is a poor choice of word for this discussion ?

The certification rules go into the design and TC process (and often end up in flight manual prescribed instructions) and are hard requirements for normal operations. In the event of a problem, either you will have approved guidance material (which can be assumed to supersede the original rule) or you may need to invoke command authority ... but you can't dismiss the certification rule just because you don't like it.

Certification standards cover a presumed set of circumstances, certainly not every situation which might arise. Only when the latter occurs, should one consider throwing out the rulebook after due consideration. As a wise regulatory authority chap suggested to me years ago when I was jumping up and down trying to get a local rule varied .. "First, young John, make sure you know the thinking and history behind the rule which it is you might wish to abandon .. "

discuss what altitude would be a good compromise

One is certainly not going to descend in the event of a drop down mask failure if that is likely to compromise getting to an aerodrome, avoiding terrain and so forth, so this view is reasonable. Like with most problems which might arise, a bit of thoughtful reflection is a useful strategy to adopt.

[giggitygiggity]

Not sure why you'd get bogged down in the maximum legal altitude over the maximum sensible altitude? The max sensible altitude would surely be 10k of 13k for <30 mins. You can't comply with the ECAM in the event of a decompression unless you're below 10k, so why bother trying to argue the point? Save yourself the hassle and just go down to 10k and divert as required. If a TRE desperately wants to argue the minutiae of what's legal/illegal when faced with an obvious airmanship scenario, you're doing your upgrade at the wrong airline.

What I don't understand is why you'd ever consider continuing with an AC ESS Bus failure anyway? Just divert and get to a sensible altitude as that scenario dictates. If 'terrain is a factor', surely just remove that 'factor' and fly somewhere where it isn't. If it isn't obvious, consider/apply the MEL/ECAM ramifications as part of your diagnosis (eg FL limitations)..You're obviously not legally bound to follow it, but from an airmanship point of view, I'm sure they've thought a lot harder about a scenario than you or I could when the bells go off halfway through your cornflakes.

[Lantirn]

I agree with you, maybe you misread my previous post #16 there I explained why chose not to discuss decisions here

You may have other restrictions (endurance) to get to a CAT1 airport at 10000. My question is more academic

[FullWings]

Certification requirements are interesting but have the potential to lead you up the garden path in the real world.

Potentially an awkward view, methinks. "Interesting" is a poor choice of word for this discussion ?
I would offer an alternative opinion. In an airborne non-normal situation, you have various sources of information to go on, primarily the QRH, MEL/DDG, FCOM and various OMs. What a group of people thought up 50+ years ago to generically cover all aircraft is, in my own words, “interesting”, and could form part of the decision making process, assuming that you knew it in the first place. Will everyone die at FL260 if you can’t go any lower because there’s a mountain underneath? Also remember that we are talking about a multiple failure scenario: you’ve lost supplemental oxygen and then looking at several more failures to leave you without pressurisation.

What I’m trying to say (possibly badly) is that when you’re on the ground you can always choose not to leave it, or go flying but with restrictions, and the MEL/DDG are written with this in mind and observe any certification requirements. When you’re up there trying to figure the safest way out of a gnarly problem, at lot of that turns into advisory information, to be considered along with everything else. There are all sorts of regulations, covering almost every aspect of aviation but there’s a whole spectrum between flying at night with no lights because they’ve failed, and attempting to takeoff on a runway that is demonstrably too short. Unthinking adherence to what may be fairly esoteric requirements may lead to a less successful outcome, as you may be rejecting solutions that would be more effective overall.

[FlightDetent]

Lantrin, best of luck!

Trying to respect your RoE, FL140 from me.

On a type certified for flight above FL250 you shall provide O2 to 30% passengers after DX between FL140-FL150 and 100% pax above FL150. CAT.IDE.A.235 Table 1. Since you don't have the equipment anymore, choose a flight profile that satisfies the requirements.

Terrain and fuel shouldn't be a factor, solved already at the dispatch phase.

Well, perhaps not always. For non-LROPS flights, the 60 minutes distance requires only adequate airports so the actual WX might officially be poor. Then FL250 for endurance, if really required. :\

I think the inspiration from AMC1 CAT.IDE.A.235(e) is acceptable only if the appropriate rules cannot be followed due to overruling reasons. Not by choice.