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Always be on the lookout for signs of hypoxia


During our training, we memorized CAR 605.31 and 32 which state that for flight between 10,000 and 13,000 feet we must have enough oxygen on board for the entire period of the flight exceeding 30 minutes for all crew members and 10% of the passengers, but for not less than one passenger. For flight above 13,000 feet we must have enough oxygen on board for the entire period of flight above 13,000 feet for all persons on board.

Many of us ignore these regulations as we do not normally fly at these altitudes for any length of time and we overestimate our ability to fly at altitude without supplementary oxygen.

The pilot of a Piper Warrior encountered IMC conditions in a valley at 3,000 feet. He didn’t feel he had time to turn around and stay in visual contact with the ground so he climbed straight ahead in the valley and hoped to climb above the cloud quickly. He was at 9,500 feet before broke out of the cloud tops. He made several transmissions to the Kamloops Flight Information Centre before he made contact with them at about 9,000 feet. He was given a Vancouver Centre frequency and then radar vectors and a clearance to fly at 10,500 feet to Boundary Bay when he was able to descend visually for a landing.

A Cessna 182 pilot filled VFR Over The Top. The forecast cloud tops were 8,000 feet until just short of his destination, where he expected to be able to descend visually for landing. Initially, the cloud tops varied between 8,000 and 8,500 feet, but then the tops began to rise gradually to about 11,000 feet.

He was on top for almost two hours, one hour and 10 minutes of that was above 10,000 feet. After landing, he complained about a low grade headache that lasted several hours.

The pilot of a Piper Arrow was climbing through 7,500 feet when his eyesight began fading rapidly. At 8,500 feet, he could barely see a thing although it was mid afternoon and without a cloud in the sky. He reduced power and began a descent. His eyesight returned as he descended.

Our brains and our eyes require more than 70% of the oxygen we consume. The brain and the eyes need oxygen to rebuild and maintain the chemicals that are necessary for thought processes and sight. Any reduction of available oxygen will give us a sense of complacency and possibly a sense of euphoria. It reduces our ability to think or concentrate, therefore reducing our ability to make good judgements.

A reduction of oxygen also reduces our visual acuity and our ability to process what we see. Since our ability to concentrate is affected by a lack of oxygen, we may become disoriented. More emphasis is now being placed on disorientation during instrument and night flying training. It is possible that some of the accidents and incidents that have been blamed on disorientation may have stemmed from a lack of oxygen.

The early signs of hypoxia are a general feeling of fatigue or drowsiness and/or a low grade headache. Later symptoms may include blue lips or blue finger nails.

We are not all the same and a lack of oxygen will affect each of us differently. Our general health, our level of fitness and our age affect how we process oxygen. Smoking affects our ability to process oxygen. Poor nutrition and illness (even mild not feeling quite right) make us more tired more easily. Fatigue increases the possibility of hypoxia and hypoxia in turn makes us feel more fatigued.

Temperature affects a pilot’s tolerance to hypoxia. Extreme heat or extreme cold conditions make our bodies work harder to maintain core temperature within acceptable limits. The energy expended in doing so is what decreases our tolerance to hypoxia.

The pilots of the Piper Warrior and the C-182 were under the age of 45, were reasonably fit and were non-smokers. The Piper Warrior pilot didn’t complain of any symptoms of hypoxia, but his adrenaline level would likely have masked such symptoms. The pilot of the Piper Arrow was in his 50’s, was overweight, was out of shape and was a heavy smoker.

We must be aware of the conditions where we may experience hypoxia and of the signs of hypoxia. We must also be prepared to get to a lower altitude or land if those signs manifest themselves. We should also watch for signs of hypoxia in our passengers. They do not have as much experience at altitude as we do and therefore may exhibit signs of hypoxia sooner than we do.

There is the possibility that if they are feeling hypoxic we may be slightly so ourselves or will be soon. They may not be flying the plane but we should get them (and ourselves) to a lower attitude as soon as possible.

The FAA recommends that all pilots use oxygen when flying at night above 5,000 feet. At night, we normally have lower visual acuity and the reduced oxygen level above 5,000 feet will lower it even more.

Small oxygen bottles aren’t expensive and oxygen isn’t expensive. If aviation oxygen is not available, medical oxygen will do. We should consider using supplementary oxygen whenever we are planning any flight above 5,000 feet for long periods. It will make the flight more enjoyable, less tiring and safer.

We should not plan long flights at altitude if we are tired, or not feeling well. We should always watch ourselves for signs of hypoxia. They are subtle. We are too complacent about the affects of hypoxia and hypoxia makes us even more complacent.

Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently flies medevacs from Victoria in a Lear 25. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.