Training Tip: How bad leads to worse

Not only is “localized” starting to seem a poor description for the gray-white vista spread out below, but the layer, which has closed to a solid overcast—for you, an undercast—appears much closer to your aircraft than it was a few minutes ago. So you add power and begin a new climb to put some air between you and the clouds.

Funny thing about cloud tops: They don’t always stay put. When they rise, they force you and your stress level ever higher. Meanwhile, something else is heading lower: The amount of oxygen in your blood.

Remember your ground school study of hypoxia? It’s a deficiency of oxygen reaching the tissues of the body that can lead to muscular impairment, impaired judgment, and loss of consciousness—and it may already be affecting your judgment in the flight scenario depicted here.

You might have learned about hypoxia around the same time you perused the flight rules on supplemental oxygen. Unless you train at a high-elevation airport, you may have dismissed those rules as testable material not applicable to your own flying.

Here’s the problem with that notion: A repeating theme in incidents reported by pilots flying VFR in light aircraft who came to suspect hypoxia as a causal factor in a deviation or an emergency situation is that the hypoxia risk was the last thing on their minds when they confronted their in-flight difficulty.

Usually the pilots involved had not planned to fly at altitudes where oxygen might become a concern, so they had taken no precautions such as having a pulse oximeter on board.

The reports also often confirm a well-known, insidious characteristic of hypoxia: The hypoxic pilot tends to be the last person to realize he or she is in trouble. Several reports filed with the Aviation Safety Reporting System record that a pilot in a second aircraft, or an air traffic controller, noticed signs of the pilot’s impairment and prevailed on the stricken individual to descend, or land.

Reading aviation safety reports filed by pilots who wondered if hypoxia had influenced bad decisions made in flight is a bit chilling. But some reports also contain useful observations.

As one pilot wrote, “If you think, ‘I wonder if I'm hypoxic,’ then you need oxygen.”

Do you think you have ever had hypoxia in flight? Share your insights at AOPA Hangar.com.