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Guest jrewing

Flying non-pressurized aircraft in the flight levels

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A post about the Mooney Bravo got me to thinking.How comfortable is it for pilots and passengers to fly with Oxygen in the flight levels? Is there a certain limit that one can tolerate flying with an Oxygen mask, and/or tolerate flying with such a low air pressure?I've always been a bit curious about this, since TC aircraft are very common and always advertise the cruise speed they attain in the flight levels.-John

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It is not comfortable at all. But for Part 91, you can fly for up to a half an hour between 12500 and 14000 without any supplemental oxygen. Above those altitudes, you and then your passengers will need oxygen for the entire time. The typical O2 bottles that you would use for your masks can usually last about two hours. You can either use a mask, a nasal canula, or some people would rip the device apart and just suck on the O2 through the mouth.

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>are very common and always advertise the cruise speed they>attain in the flight levels.If I am not mistaken it is not the cruise speed but economy that counts. The best cruise speed is usually attained in lower than max ceiling altitude (depends on type of engine) but the higher you can fly you normally get the best range (specific range - miles per 1 gallon of fuel).Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2

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Hi John,This is from memory, but I believe the use of a nasal cannula is not allowed above a cabin pressure altitude of 18,000'. A diluter system with a mask and re-breather bag is allowed up to 25,000'. Above FL250, you need a diluter-demand system, and above FL3500 you need a pressure demand system, as I recall. I don't think you'll be getting above FL250 is a non-presurized turbo-charged piston aircraft, unless you are Bruce Bohannon!Several manufactures that have created diluter systems that allow you to dial in your cabin pressure altitude and the flow of oxygen is adjusted accordingly, which can considerably extend the useful supply of even a small tank. I have a small SkyOx system with such a flow control system that will last for nearly four hours at 15,000' for one person or 2 hours for two persons.On a recent cross country trip in a Cirrus from the SF Bay Area to San Antonio, the plane's owner and I found 6+ hours at 11,500' had left us with a good case of "the stupids" on the ground at El Paso. I used O2 most of the way back (over 8 hours spent at or above 10,500) and it left me feeling much fresher and more alert. The downside is that my sinuses felt a bit dry and irritated at the end of the flight. Prolonged use of O2 can create some really nasty side effects, so you're better off limiting how long you use it or go in a pressurized aircraft. Besides, one of the great things about GA flying is being able to see the terrain, which you can't really do at high altitudes.One usually does get better cruise speeds AND fuel economy at higher altitudes. Flying at higher altitudes can also let you take advantage of winds aloft, which can result in spectacular groundspeeds if you are headed the right way.John

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