8 thoughts on “Flying High Unpressurized

  1. Hi John,
    I very much enjoyed your article on flying high, as we certainly can relate to all the problems associated with it. My wife and I are both instrument rated private Pilots. We have been flying together since 2001 with our C 172 and C 182’s. In 2012 we bought a 2009 Turbocharged C 206 with tip-tanks, and we regularly fly at FL180 from where we live to Orlando, Miami or similar Florida destinations, averaging 3-4 hour crosscountry flights. Our onboard O2 lasts the 2 of us for about 5 hours, and we never had any reasons to worry about our supply. What we where not aware of is that the tubing on the cannulas will get brittle after some time and should be replaced every 2 or so years. We found out the hard way, at FL180 as my wife looked at me somewhat confused and pointed at her flowmeter which was at zero.
    My first reaction was to switch her supply to one of the backseat ports , which did not make any difference. It was at that stage that I checked my meter and it also was at zero flow. We where out of Oxygen! I requested, and got assigned a lower altitude from ATC immediately, but it already was a enormous task to initiate the descent on the G1000 due to fast on-setting hypoxya.
    We recovered fast at the lower altitude, and landed in Orlando without further incident. Both our cannulas had cracks at the pressure side of the Tubing (before the flowmeter) and we had leaked our O2 supply.
    Lessons learned: My preflight now includes testing for leaks by turning on the O2 system.
    I have replaced the tubing (available as a Kit from the original supplier ). We have one each spare cannula ready and tested on the back seat (not plugged in).
    On the G1000 I have initiated a Alert to check the supply gauge every 30 minutes. I do now fill my own O2 and I am maintaining a 100Ft2 decicated Scubadiving tank with 3000 PSI of Oxygen, filled by the local Scubadiving store that does technical Diving. This also cut my O2 cost by over 50 % and I now fill my onboard Tank to the max of 2000 PSI
    and not as normally done by the Airport supplier on the Cascade systems to 1700 PSI ( if you’re lucky) for $ 150.–.

  2. Thanks for the comment; we’ve updated the article. Mountain High confirmed they currently only have 1- and 2-place systems.

  3. I have heard that there is a sense of euphoria when experiencing hypoxia. Or would it be during hypoxemia? Hypoxia seems to be the result of hypoxemia. My son is a doctor and says there is frantic involuntary body reaction from hypoxia.
    Is the euphoria I heard about as a student pilot a myth?

  4. i flew a 231 Mooney for 15 years and discovered that whenever I flew above 10,000 feet for a half hour that I felt lously for the next two days. Oxygen is cheap! Turn it on above 9000 feet
    Dave Barker

  5. From Dr. John Levinson: Different people definitely have different reactions to not getting enough oxygen. As the doctor looking at the patient who doesn’t have enough oxygen, confusion is common and more or less universal, sooner or later. It may be calm, but it is often agitated confusion. The subjective sensation is much more variable from person to person and more difficult to know. Early on, a sense of euphoria is certainly possible, but it could also be quite the opposite—a sense that things are really not right. This variability is why I suggested that a pilot who flies high unpressurized should at some point find out what their symptoms are because it will give them the best chance of recognizing hypoxemia, should it occur.

  6. Don’t disregard the danger of oil/grease around oxygen, particularly if pressurized. I have seen the low pressure tubing of a military airplane expanded to look like sausages, necked down at each wall clamp and at fittings because of a contamination causing a low order detonation inside the line. No leaks either.
    Also suggest sniffing each bottle of o2 before installing or using it. One of my mechs installed an O2 bottle on a B727) serviced by an approved vendor. The flight crew on their preflight tested their masks and nearly passed out. The valve seal , we deduced. must have combusted because of over-rapid filling. Bottle was full of contaminated O2. Before using a new bottle or after filling, perform a “Sniff Test”. Simple, crack valve momentarily away from you, then waft released gas toward you, if its bad, you will smell it.

  7. I once saw a commercial diver in a recompression chamber on a boat in the Gulf of Mexico, breathing 02 thru a rubber mask when the rubber self-ignited. He got rid of it quick and we got him out with a black ring on his face and into another chamber. Spontaneous combustion in high-O2 conditions is real.

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