On ground
7 min read

As a late blooming, somewhat studious private pilot who earned his certificate at age 75, I certainly learned, knew, and could recite the Federal Aviation Regulations that relate to the use of oxygen while flying at altitude in an unpressurized aircraft—no doubt. I did not really understand, much less comprehend, however, just how dangerous a situation a pilot can find himself in when actually experiencing real hypoxia until a recent cross-country flight from Oregon to Wyoming to visit my grandson at his summer construction job.

While flight planning, I chose a route of flight that would take me across the states of Oregon and Idaho on Victor airways 500 and 4 that would lead to a fuel stop at Rock Springs, Wyoming (RKS), and leave a short leg up to Casper (CPR), our final destination. I determined an eastbound altitude of 11,500 ft. would provide sufficient vertical clearances from terrain and reasoned 12,500 ft. on the way home would provide some extra cushion along our sometimes-mountainous VFR route on the same airways.

Boost oxygen

Disposable oxygen bottles can help, but only if you have enough—and only if you use them.

The thought of 12,500 ft. prompted me to pick up a few cans of supplemental pure oxygen just in case it was needed on the way back, as the 12,500 ft. altitude kind of triggers the use of supplemental oxygen—so I thought. Little did I know what could happen to me in such a situation.

After getting airborne, heading eastbound and crossing the Cascade Mountain range on what started out to be a beautiful Saturday morning, I noticed what I felt was a little dizziness and a slightly uncomfortable feeling within the first few hours of a five-hour leg. Smoke from forest fires also shielded a good view of the ground, making what started out as a fun flight fade into uneasiness as we flew along. I decided to try breathing a little oxygen en route, even though in my mind I was thinking we weren’t anywhere near where we needed that stuff yet.

I was somewhat muted as a pilot and felt OK, but when crossing over Bear Lake near the Idaho-Utah border, my son, who was with me as a passenger, became extremely quiet. Upon rousing him a little, it became very clear that he was about to pass out. Although I thought his symptoms could be diet related, I got him going on gasps of oxygen as well to see if it helped. I noticed his fingertips were turning a little white in color. I offered to make a landing at Kemmerer (EMM), a place I had picked as an alternate fuel stop, but was relieved when he said no and would try to make it the 70 miles we had remaining into Rock Springs.

Thank God for his Army Ranger training. Honestly, I was a little relieved as by this time I did not feel all that sharp as an aviator and preferred to follow my original plan as I was familiar with it, rather than lose altitude quickly to get on the ground and see just how we felt.

After a little extended break at RKS, we headed northeast to Casper, again flying at 11,500 ft. Some fairly strong updrafts and downdrafts prompted me to turn off the autopilot and fly manually to maintain course and altitude and it was in doing this I noticed I could just not quite make corrections quick enough to be doing a good job with it—but I really didn’t know just why I was having so much trouble.

Once we got on the ground, all was forgotten so we could enjoy a quick visit, which did include some golf as well as a discussion of the fact that we may need a lot more oxygen on the way back as we would be flying 1,000 feet higher going west. When we stopped at the sporting goods store to buy a case of oxygen canisters after golf, the checkout person said we must have had a tough day on the golf course if we needed that much oxygen after it was over. Funny but true in our case.

On a grand departure westbound out of Casper, we climbed to 12,500 ft. and were enjoying finding mines and power plants when that dizzy, unbalanced feeling took over again within the first 100 miles. We started breathing with a lot more supplemental oxygen pretty much from reaching altitude but the feelings of being mentally distracted and somewhat out of it got worse. Over Bear Lake once again, but this time with a long way to go, I struggled with the decision and implementation but did descend down to 10,500 ft. to see if we could shake that sort of paralyzed, incapacitated feeling, but it didn’t get much better.

When we got near Boise, ATC diverted us for traffic and as I switched out of autopilot to be responsive, I found that I could not adequately control the aircraft to normal standards. When I lost some altitude, I would slowly correct, then realize I had lost course and tried to fix it while losing altitude again. Everything was in slow motion, sort of like falling asleep at the wheel after a long drive, or being a little drunk, and it was difficult to reason why this was happening. I didn’t understand it at the time.

On ground

We made it, but why do we feel so bad?

When ATC gave us back our own navigation, they actually called to confirm we had it as our track was not appearing to them like we did. We slowly got control and as we continued on to our scheduled fuel stop, more “normal” pilotage came back into focus with time and of course, oxygen, but I never quite got a completely good feeling through it all. We completed the adventure successfully but it took a few days on the ground to shake that unstable feeling and prompted a lot more study of what the real dangers of hypoxia are to any pilot.

That study, along with some internal discernment, led me to the following suggestions that might help fellow aviators:

  1. Take hypoxia seriously. We all know 14 CFR 91.211 calls for supplemental oxygen on flights at or above 12,500 ft. for any stretch over 30 minutes, but I didn’t take that seriously enough in my flight planning. If I would have thought about the fact that, by regulation on my return trip that meant I would pretty much need oxygen full time, I would have been better prepared for that and might have chosen 10,500 ft. as it would have worked for most of the route. Not enough attention was paid to the real risks here.
  2. 10,000 ft. is a good baseline. Post-flight studies revealed that many sources verbalize the fact that although the regulations use 12,500 ft. as a cutoff for supplemental oxygen, going above about 10,000 ft. is really a better delineator to assess the risks of actually experiencing hypoxia at altitude. This is my new marker for altitude and oxygen on future flights and I recommend consideration for others as well.
  3. Recognize the symptoms. As part of my post-flight evaluation on this trip, I looked back at past flights to see if I had felt like this before on previous trips. Although I had completed several earlier cross-country flights at the 11,500 ft. without incident, I did recall one occasion while going from Bakersfield to Thermal, in California, the sensation of feeling out of balance or some dizziness that was similar to the initial onset of the hypoxia experienced on this much longer flight at the same altitude—which I could not readily identify at the time. I now know what the onset of insufficient oxygen feels like.
  4. Symptoms are progressive. The effects of hypoxia progress with time in the air and degrade the pilot’s ability to just fly correctly. The longer the flight, the worse it gets. In my case, it started with dizziness or an unbalanced feeling in the head I had felt on that one earlier flight but could not identify, then progressed to some form of loss of cognition, which manifested itself by way of slow reactions and loss of motor skills. Ultimately, a sort of grogginess and loss of comprehension as to what was happening came upon me that lead to a surreal feeling and some real struggles with basic flying skills that are normally present. Serious stuff.
  5. Beware hypoxia! It is real. It can affect different people in different ways and at different altitudes. It can be dangerous if you’re not prepared for it, as I learned. Make it part of a risk assessment on flight planning when appropriate. And most of all, enjoy each flight. We can’t do this stuff forever.
Natt McDougall
Latest posts by Natt McDougall (see all)
24 replies
  1. Chris H
    Chris H says:

    Thanks for sharing your experience. I think that you highlight a really important trap for new pilots with respect to hypoxia. It all seems so simple because the FARs present really straightforward guidelines for O2 use. The problem is that different people experience hypoxic effects at different altitudes. I learned this the hard way when I did a mountain flying course out of Rocky Mountain Metro as a flatlander East coast pilot. One of the highlights of that course was landing at Lake County Airport in Leadville, CO. Approaching the airport, I became confused and could not visualize how to enter the pattern for the correct runway. Though we were below so-called oxygen altitudes and the local Colorado-based instructor did not think we needed oxygen, I certainly did. The problem was obvious to me in hindsight, but like you, I did not realize what was happening right away. Later experience has shown that I get headaches if I spend more than an hour or so above 10,000 feet. I know many pilots who understand their own physiology well enough to know that they need O2 at lower altitudes than those mandated by the FARs. I think I just met another.

  2. Rich R
    Rich R says:

    getting to know your body’s reaction to flight stressors is as important as knowing your aircraft and ops environment…it’s critical to recognize diminishing performance early and take definitive steps while your head is still in the game.

    another threat for incapacitation is CO poisoning, while not an AME, the several days of lingering fog after the flight would make me want to take a good look at exhaust system integrity and cockpit ventilation with your mechanic…and when experiencing “fog” symptoms in the air, opening every fresh air source and expeditiously getting lower, or if the “fog” doesn’t immediately clear, on the ground ASAP.

  3. McCague Jamie
    McCague Jamie says:

    Great story ,good advice and tips , here’s another : anyone flying at 10000 feet or above (in unpressurized AC) should always have a PulseOximeter on board , if going to 10 start checking at 8 , it measures the oxygen concentration in your blood, if reading below 90 , add oxygen.

    • Propwash
      Propwash says:

      Your O2 needs can be different on any given day as well.
      Most days I am ok at 12k but sometimes I feel the need at 10k.
      Women respond better to starting O2 at lower alt than men.

      My father flew non pressurized Air Force transports for 20 years and I remember him saying they slap on the O2 mask at 10k.

  4. Ray Bracis
    Ray Bracis says:

    I obtained my certificate at 74 and based upon advice from my instructor and our own experience, my wife and I use O2 in any flight approaching 10,000 ft. You just feel better and aside from a slight headache that magically disappears when the oxygen begins to flow, we have had no untoward effects. We also use oxygen tanks for a continuous flow.
    Ray Bracis, M.D.

  5. Allen Kerr
    Allen Kerr says:

    Hypoxia is especially a risk for those who live at low altitudes. espially sea level. For those who live at higher elevations, 4000 plus, they generally have a little more leeway.

  6. George
    George says:

    I am 72 and back on Mother’s Day this year I was flying back to New York to see my mom. VFR from Topeka, Kansas to Ft Wayne, In. From Ft Wayne to 1B1 I was going to be IFR with icing forecast from 8000 to 20000 ft. I was at 7000 and started to get ice. Was cleared to 11000 so went on oxygen as I started to climb. Later was cleared to 13000 due to more ice. Any time I’m going above 10000 in solid IFR I always get on oxygen before I get there.

  7. Pierre William Senneville
    Pierre William Senneville says:

    I flew all my life and still do. Above 10,000 for 30 minutes + it’s O2 and at night at 6500 pa plus it’s also O2. I found that after 60 years old my tolerance to hypoxia is quite lower. I have been trained to recognize it, but honestly it’s not always the same. Thanks for sharing, but reading up on it is quite revealing. Happy landings.

  8. Dave Macdonald
    Dave Macdonald says:

    A few years ago I got the chance to safely experience hypoxia at a workshop put on at our local airport by the FAA FAAST team. They set up a “tent” that allowed them to reduce the O2 content inside, and invited all the local pilots interested in the safety training experience to make an appointment to participate. We started off with some ground training on the effects, and then they walked us into the high altitude tent, initially donning a mask and with an O2 finger sensor. we were then instructed to remove our masks, as start doing math problems they provided.

    What surprised me was that there were a couple of much younger pilots than me who rapidly became disoriented and were helped to don their masks, while a couple of 60+ year olds, including me lasted much longer (only a few minutes). So age isn’t necessarily a predictor of how your body will respond.

    This was a great way to experience the symptoms and find out how my body reacts, while also driving home the need to carry oxygen on flights at higher altitudes. I strongly recommend your flying club check with your local FSDO office to see if a similar experience is still offered and available for your airport.


    Years ago I recall reading that the 12,500 for 1/2 hour or more rule was created back in the old air mail carrying days where it took just less than 1/2 an hour to cross the Rockies….therefore no oxygen needed. It really had nothing to do with physiology. It was driven more by frugality..

  10. James Geyman
    James Geyman says:

    Good article! I find I also get dizzy and slow above 12,000 feet at age 60. A o2 setup is a real life saver, and well worth the $250 or so for a small tank. I am amazed to find my pulse ox reading at 88% or less, at 11,000 feet or more at times. For a X/C trip it sure keeps you more refreshed.

  11. Barry Gloger
    Barry Gloger says:

    All west coast pilots routinely fly at altitudes, where measurable performance degrades due to oxygen depravation. Therefore, I as a physician, pilot, and former flight surgeon, and the Aviation Medical Societies recommend that all all west coast based planes carry supplemental oxygen and pilots use it over 7,500′, especially at night.

  12. Sandra Williams
    Sandra Williams says:

    I fly skydivers at a very busy drop zone in Florida. When interviewing for the job, one of the first things I mentioned was that I would need supplemental oxygen on all flights above 10,000′. This elicited a strange look and a query as to why? to myself, I thought “every skydiving pilot should wear O2!” but instead pointed out that I had a fairly weak respiratory system and would do better with oxygen. I am very aware of hypoxia – and find the symptoms quite obvious. Starts with getting a bit stupid and making small mistakes. Anyway, they were very accommodating and in the six plus years I’ve flown there, I always have a tank next to me. My record number of flights in one day is 27! No one can say that 27 times going above 13,500′ isn’t going to affect performance. At first, the skydivers looked at me like I had two heads – such an uncool pilot to have an oxygen canula in her nose. But having explained to a few people that my first responsibility is to keep them safe while they are in the plane with me – not one peep since about my uncool appearance. And you know I am sharper and feel better at the end of a super long day because of the supplemental O2.

  13. Edward Drum MD, Capt. USNR-ret
    Edward Drum MD, Capt. USNR-ret says:

    I’m a retired USN flight surgeon and all of us aviators undergo Physiologic testing and physical tolerances, but oxygen deprivation in the Chamber run is quite dramatic.. Eight to ten members are placed in a chamber with aviation corpsman assigned to task us with various dexterous puzzles while off O2 in trail runs at various altitudes. The purpose is to recognize symptoms before loosing consciousness. My task was to place various sized blocks into a round ball, challenged with receiving holes that match the blocks.. We were certainly above 10,000 ft when the experiment in recognition O2 deprivation began. Off O2 and climbing. I was determined to complete the task (also called target fixation) despite O2 deprivation. I was truly a very bad example and lost consciousness maybe at 14,000 ft and developed a “liver flap”..(Hand flopping in the wind at wrist).. The corpsmen put me on a high oxygen flow and I recovered in who knows how long a period.
    Lessons learned: Judgment and alertness are lost before fatal symptoms cause loss of control of an aircraft. Never ever be off O2 at or above 10,000 feet.

  14. Lowell Berntson
    Lowell Berntson says:

    I found that hypoxia can occur at less than 10k feet. Now that I have experienced it at 6000 feet and know what to watch for I always have the O2 hooked up and ready to use. The point is that it can happen well under 10k feet and it is hard to predict.

  15. David
    David says:

    Transport Canada (the Canadian version of the FAA) mandates oxygen use above 10,000′ after 30 minutes and recommends oxygen above 5,000′ for night operations.

  16. fred northup
    fred northup says:

    I wonder why it affected you on this flight and not prior flights. Plus you were on O2 so why didnt that solve it? You might want to look into other issues like exhaust leaks?

  17. Russ Paris
    Russ Paris says:

    Thanks for sharing your experience. You mentioned forest fires obscuring view of the ground; a byproduct of combustion is carbon monoxide (CO), which can take up to 48 hours to clear from your blood. That might, or might not, have been a contributing factor. The FARs do a specific job defining oxygen parameters within a regulatory context, but hypoxia itself doesn’t present itself so neatly. Skiers, mountain climbers, and sports enthusiasts going to altitude quickly are familiar with the more generic sounding “altitude sickness” definition. Larger medical websites can offer further explanation. Since you’ve been restoring your 206, you might consider a 2-4 place portable oxygen system for those missions above 5,000 MSL. Or maybe postponing a flight that requires traversing vast swaths of wildfire smoke. Wishing you tailwinds and clear skies.

  18. Neil Sidwell
    Neil Sidwell says:

    In Australia pilots are required to continuously use supplemental oxygen when flying unpressurised aircraft, and flying above 10,000 feet. For about AU$70 you can buy a finger oximeter, and I also have a portable battery powered CO meter strapped in the cockpit of my plane which will shriek if the CO levels start to get too high. It cost about AU$75. So for under AU$150 (about US$110) you can have early warnings if your oxygen levels get too low or if CO levels are getting too high. Considering what we pay for fuel these days I would consider the above a worthwhile investment.

  19. George Hamilton
    George Hamilton says:

    Night need O2 takeoff to landing, try flyi
    ng about 4000msl then turn on the O2. Instrument light will brighten.

  20. Ray L Rivera
    Ray L Rivera says:

    Dr. Drum’s advice (about seven replies above mine) is wise and sound. No two people react the same way under the effects of hypoxia. As a private pilot it would be wise to schedule a visit to the FAA CAMI (Civil Aerospace Medical Institute) at the FAA campus in Oklahoma City to find out how you’ll react while hypoxic in the CAMI PROTE (Portable Reduced Oxygen Training Enclosure) chamber. It’s worth it and it can possibly save your life someday.

  21. James Dickson
    James Dickson says:

    On a recent cross country flight at 9,500 with my son, I recognized some mild hypoxic symptoms. My son (25) and I am 63, my son felt that he was not experiencing any hypoxia symptoms, on decent my symptoms cleared right up. During a career as an enlisted aircrew member for the Air Force of more than 22yrs, I had periodic training in an altitude chamber which was invaluable. Early in my career, during chamber rides I enjoyed trying to function at the various cabin altitudes with my oxygen off and mask to the side, results were mixed but overall I thought that I was pretty strong. Later in my career, I wanted my mask on (oxygen on and 100%) almost immediately, as soon as I felt hypoxia symptoms, and I no longer had any interest in doing puzzles and watching the colors flood back. Lately I have been considering investing in a two place portable oxygen system for flights above 7,500 feet or so. Aircraft are usually pressurized to 8,000 feet during day light and 5,000 feet at night for better night vision.


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