Aeromedical factors

Hypoxia

Hypoxia is a lack of oxygen reaching the body's tissues. Four types:

• Hypoxic: not enough oxygen in the air, like at high altitude.
• Hypemic: the blood can't carry enough oxygen, for example because of carbon monoxide or blood loss.
• Stagnant: poor blood circulation, such as from high G-forces.
• Histotoxic: cells can't use the oxygen, for example from alcohol or drugs.

Symptoms include euphoria, headache, slower reactions, impaired judgment, tingling and blue fingernails or lips. The danger is that hypoxia feels good, so you might not notice. Night vision suffers first, even at moderate altitudes.

Carbon monoxide

CO is odorless and comes from the exhaust. In many airplanes the cabin heat is warmed by the exhaust system, so a crack can leak CO into the cabin. Symptoms: headache, drowsiness, dizziness. If you suspect it: turn off the cabin heat, open the fresh air vents and windows, use oxygen if you have it, and land. A cheap CO detector is a great investment.

Hyperventilation

Breathing too fast (often from stress or anxiety) lowers carbon dioxide in the blood, causing dizziness, tingling and lightheadedness, which can feel like hypoxia. The fix: slow your breathing; talking out loud helps.

Spatial disorientation

Your inner ear (vestibular system) senses motion, but it's easily fooled without a visual horizon:

• The leans: after a slow, unnoticed bank, rolling level makes you feel banked the other way.
• Graveyard spiral: in a prolonged turn, you stop sensing the turn; as you lose altitude you pull back, tightening the spiral.
• Coriolis illusion: moving your head abruptly during a turn creates a strong tumbling sensation. The most overwhelming one.
• Somatogravic illusion: rapid acceleration feels like pitching nose-up, tempting you to push the nose down.

The defense is to trust your instruments, and as a VFR pilot, to stay out of clouds and very dark conditions in the first place. If you do fly into clouds by accident, keep the wings level on the attitude indicator and make a gentle 180° turn back to where you came from.