O2 use over FL410

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According to my ATPL notes (JAA based), at least one pilot should be on oxygen when a pressurised aircraft is over 41,000 ft.

Is this a widely used regulation?

[Notso Fantastic]

No. The 744 has a maxalt of 43,000'. It is adequate to have immediate donning equipment available. The 744 O2 is an inflatable headband that inflates as you put it over your head then immediately contracts when released. If you take 5 seconds (including removing your glasses), you're a slowcoach!

[hoofhearted]

Our B744's have a max altitude of 45100'. Above 41000', then at least one pilot must be on oxygen.

[StressFree]

I've flown a Gulfstream 4 at 45000' many times without either of us being on oxygen. As previously stated its OK to do so as long as you have quick-donning masks (usually Eros.....).

:cool:

[speedbird_heavy]

Concorde flew at hights of up to FL600 and I never saw any of the 3 flight deck with their oxygen mask on. So I don't think it is a must.

[Vlad the Impaler]

surely if you depressurise at FL600+ you are all for it anyway !! wouldn't the thing just disintegrate ?

[Tinstaafl]

Vlad, pressurised a/c aren't like a balloon that's completely sealed to contain the higher pressure air. They're more of a seive, continually leaking but with air being pumped in faster than it can leak out. An outflow valve is used to finely moderate the rate of leakage at one or two points to control the internal pressure.

All it takes for a depressurisation event is for the overall leakage to exceed the pressurised air inflow ie an exacerbation of what is happening normally & continuously. That doesn't necessarily imply catastrophic breakup.

[Semaphore Sam]

FAR 91.211(b)1(ii) implies that someone has to be on O2 above FL410.

[northwing]

Time of useful consciousness above 41000 ft is 12 seconds - the time it takes for the blood to get from the lungs to the brain. Hence the rule is that one pilot should wear the mask above that altitude. Pilots generally don't like wearing a gas mask for hours in the absence of any obvious likelihood of depressurisation and hence are tempted to ignore the rule. After the latest generation of long range jets (777, A340, Global Express etc) came in the FAA descended on a few hapless specimen victims, politely enquired as to how they could have flown that long above 41000 ft and still arrived with the oxygen contents still showing "Full", and pulled their licences. After that the incentive for asking for a climb to above FL410 seemed to be less powerful.

Concorde was a bit of a special case. The reason it had such tiny windows was so that the cabin pressure didn't drop too far too quickly if two of them were shot out by a hijacker. (Really, that was the design requirement.) Whether the pilots didn't wear oxygen masks because they didn't need them or because nobody thought of it, I am afraid I don't know.

[plt_aeroeng]

VLAD

“surely if you depressurise at FL600+ you are all for it anyway” I agree.

From my memory of aeromedical training, the partial pressure of blood is equal to a pressure altitude of about 56,000 feet. For that reason, many militaries specify that fast jet crew flying above 48,000 feet (even tho cabin altitude <25K) must wear pressure suits.

In the range below FL480, time of useful consciousness would be the primary concern.

The time of useful consciousness without supplemental oxygen reduces rapidly over 35,000 feet. I have heard on the R/T or been briefed in squadron of instances when fast jet crews operating as low as FL250 suffered hypoxia without recognizing the condition. Even if decompression at FL410 is not catastrophic, an occurrence of a rapid or moderate decompression rate may result in time lag to recognition and is likely to mean reduced awareness by pilots with some difficulty in putting on even a rapid donning mask.

Such considerations are presumably why, as noted by Semaphore Sam, FAR 91.211(b)1(ii) mandates use of a mask above FL410, so that safety margins are not reduced.

I have almost no knowledge of Concorde operating rules, but in order to avoid a mask mandate, one would think that the makers and operators would have had to demonstrate to the CAA that the likelihood of a rapid decompression without immediate crew warning was very small. Northwing has described how that might have been the case.

I would also think that a Gulfstream, with a smaller cabin volume, would be more susceptible to rapid albeit non-catastrophic decompression than a wide body. In that case, it should be more important to follow the FAR rules. Don’t know if StressFree is a non-US operator, but if he is a US operator then he has been violating the FARs.

It may seem that a pressurized cabin is a comfortable environment, but there is still the possibility of failures which take us into the danger zones.