I feel sleepy

We all know about the regulation that stipulates that we not fly above 10,000 feet for more than 30 minutes or above 13,000 feet at all, unless we are breathing on board oxygen. Few of us pay enough attention to this regulation.
Last month’s column described a Mooney pilot flying under VFR OTT flight rules who had to climb to 15,000 feet to remain clear of cloud. The report this description was taken from did not say how long this pilot had to remain at 15,000 before he was vectored to VFR conditions north of Winnipeg, but it had to have been at least 15 minutes, and more likely was considerably longer.
The pilot of a Seneca 2 filed IFR at 12,000 feet direct from Castlegar to Prince George, B.C. The weather was unsuitable for VFR in the Castlegar area, but was expected to improve to VFR conditions about 100 miles north. The pilot did not have access to oxygen, but reasoned that he would be able to cancel his IFR clearance and descend to VFR conditions within 30 minutes. The forecast was wrong. The cloud did not clear to VFR conditions, and after one hour of flight, and the pilot was forced to climb to 14,000 feet to comply with IFR minimum en route altitudes. He was airborne for one and one half hours above 10,000 feet, including 30 minutes above 13,000 feet, before he was able to descend to below 10,000 feet in VFR conditions. The pilot later reported feeling quite tired before he was able to make the descent.
Pilots in British Columbia regularly fly for periods of longer than 30 minutes above 10,000 feet to maintain terrain clearance while flying above the mountains on direct routes between airports. They get away with it once and think the regulation has no basis, at least for them.
All of these pilots were risking their lives, and the lives of any passengers who were relying on them.
Hypoxia is very insidious. It creeps up on us slowly. Our brains and our eyes use about 70 per cent of the oxygen we consume. When we become even slightly oxygen deprived, our brain functions begin to slow down and we begin to feel a little tired. We do not notice it, but our visual acuity also decreases. As hypoxia progresses we may feel a dull headache and a little sleepy. Eventually we would fall asleep.
Military organizations around the world use high altitude chambers to train pilots how to cope with a sudden loss of pressurization. The chamber operators demonstrate to pilots the effects of hypoxia by asking them to remove their oxygen masks and attempt simple mental arithmetic problems or to try to write something. They prove over and over again that even simple tasks become impossible when the pilots become hypoxic, which occurs within a few minutes of oxygen mask removal. Granted, the altitudes they are working with are in the 30,000-foot range, but hypoxia can affect us even at altitudes below 10,000 feet.
All of us react to oxygen deprivation at slightly different rates, and our individual reaction rate may vary according to various factors, such as age, fitness, health, fatigue, nutrition and whether we smoke.
Age and fitness often go together. The more fit we are, the better we are able to process the oxygen we consume, and generally we are more alert. Often, as we age, we become somewhat less fit.
Even minor health problems cause us to become fatigued more quickly. Fatigue causes us to be less alert and less aware that changes are occurring to us physically and mentally. Poor, or inadequate, nutrition also reduces our level of fitness and alertness.
Smoking increases the levels of carbon dioxide in our blood and reduces lung capacity. This reduces our ability to efficiently process oxygen and will hasten the onset of hypoxia.
Add a few of these factors together and maybe on a given day we wouldn’t be capable of flying above 10,000 feet at all, or even well below 10,000 feet for any length of time without becoming hypoxic.
If hypoxia reduces and then renders impossible our ability to manipulate numbers or write, it obviously reduces our ability to analyze situations and make decisions, and it increases the risk of disorientation. The pilots in the situations described earlier in this column were lucky. The Seneca 2 pilot admitted o feeling ‘quite tired.’ He was somewhat hypoxic, and it is likely the Mooney pilot was as well. We don’t know about the countless VFR pilots who stayed at altitude too long, but likely many of them were a little hypoxic as well.
Most flights are relatively routine and do not require intense concentration, or rapid and difficult decisions, so we may get away with slight hypoxia as did the pilots mentioned. When things go wrong, anxiety and excitement increase and we may begin to breathe more rapidly and possibly hyperventilate. Hyperventilation is rapid, shallow breathing that eliminates more carbon dioxide in the blood than normal, which causes a change in the acidity of the blood, which in turn causes the blood vessels to the brain to constrict, reducing blood flow, and therefore oxygen supply. This of course would increase the rate of hypoxia. The symptoms of hyperventilation are dizziness, a feeling of coldness, a sensation of a tight band around the head, and a sensation of pins and needles in the hands and feet.
Pilots, over the years, do build some tolerance for altitude. How much tolerance we build is difficult to say, but we do become complacent to the effects of hypoxia. Non-pilots are more susceptible to the effects of altitude. If passengers begin complaining of being tired or of headaches, they are likely becoming hypoxic. We should descend to assist them, and we should descend to protect all of us, we might be soon hypoxic as well.
We can never be certain that everything will go right. By placing ourselves in situations where we may reduce our level of awareness and decision making capability; we are endangering our lives and the lives of our passengers. The rules covering altitudes and the use of oxygen were designed for sound medical reasons. Some days we may feel super human, but remember it is only a feeling.

Avoid that sleepy sensation while flying.