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Human Factors

A hypoxic pilot on the radio does not sound frightened. The voice is pleasant and slow — which is the whole reason this subject is taught as a technical one.

Technical Subject Areas — FI.II.A

The pilot who sounds fine

There are recordings of controllers working hypoxic pilots, and the hard part of listening to them is what is missing. No panic, no distress call. The pilot answers politely, a beat late, confidently addressing a question nobody asked, and has no idea anything is wrong, because the organ that would notice is the one being starved.

That is why this is a technical subject and not a lecture about being careful: almost everything here degrades your judgment before it degrades anything you can feel.

Hypoxia

Hypoxia is not enough oxygen reaching the tissues; in flight the concern is the brain. There are four kinds, and the fix depends on which one.

• Hypoxic — not enough oxygen to breathe. Its percentage in the atmosphere never changes, but its partial pressure falls with altitude.
• Hypemic — the blood cannot carry it. Carbon monoxide is the classic cause; so are anemia and a recent blood donation.
• Stagnant — the blood is not reaching the tissue. Shock, G loading and extreme cold do it.
• Histotoxic — the cells cannot use it. Alcohol and narcotics do this, and the PHAK counts one ounce of alcohol as roughly 2,000 feet of extra physiological altitude.

Memorize the symptoms, because you will not diagnose them at the time: headache, dizziness, tingling fingers and toes, tunnel vision, blue fingernails and lips, drowsiness, slowed reactions — and euphoria, the dangerous one.

Treatment is oxygen: descend, use supplemental oxygen, or both. No one is immune, and susceptibility is not fixed — it varies between people and from day to day, and the handbooks list smoking, alcohol, medication, fatigue and how well you are acclimatized as things that make it worse. Time of useful consciousness, what you have left to make a life-saving decision, shrinks sharply with altitude; the PHAK tabulates it in the aeromedical chapter. The oxygen requirements are 14 CFR 91.211, written in terms of cabin pressure altitude. Read the section rather than a summary of it: the altitude bands, the thirty-minute allowance and who has to be supplied are all in its text.

Hyperventilation, ears and sinuses

Hyperventilation is breathing too fast and too deep, stripping carbon dioxide from the blood, usually after a stressful surprise. Its symptoms overlap hypoxia almost exactly, so at altitude assume hypoxia first, then slow the breathing down.

Ears and sinuses are pressure in a closed cavity. Climbing vents itself; descending is the problem, because the eustachian tube closes against rising outside pressure and a blocked tube means real pain and lost hearing. Swallow, yawn, or pinch the nostrils shut and blow gently, and slow the descent if it will not clear. Congestion does the same to a sinus — the reason not to fly sick.

Spatial disorientation

You know which way is up from three systems — the vestibular organs of the inner ear, the somatosensory nerves in skin, muscle and joints, and the visual system. With a horizon the eyes outvote the other two; take the horizon away and the vestibular and somatosensory systems fly the airplane instead, and they are wrong.

Everything in this section is instructor-demonstrated. You cannot read your way to knowing what the leans feel like, and the place to meet them is under the hood with an instructor in the airplane, at altitude, by arrangement — not on a dark night by accident.

Each inner ear holds three fluid-filled semicircular canals over fine sensory hairs. Acceleration deflects the hairs and your brain reads a turn — but the fluid catches up in about twenty seconds, and a steady turn starts to feel like level flight. Roll out and the fluid overshoots the other way.

That mechanism produces the named illusions. The leans, the most common, is that rollout: wings level, and you feel banked the other way. Coriolis comes from moving your head during a long turn, and feels like rotating on an axis the airplane is not on. The graveyard spiral is the lethal one — the turn stops registering, so a pilot who feels the descent pulls back and tightens it. The otolith organs add their own: somatogravic reads acceleration as nose-up, inversion is tumbling backward after an abrupt level-off, and the elevator illusion reads an updraft as a climb. When your body and the instruments disagree, believe the instruments.

Visual illusions

The eyes have their own failure modes, most of them waiting on a night approach. A narrow runway makes you feel high, so you fly low, and a wide runway does the reverse. Upslope also drags the approach low, and downslope pushes it high. Three more push the same way as a narrow runway: featureless terrain, the black hole approach; water between you and the runway; and haze, which makes the runway look farther off than it is. Each of them makes you feel higher or farther out than you are, and each of them ends in an approach flown too low. Fog works the other way, feeling like a pitch up and tempting a sudden steepening. A false horizon can be a sloping cloud deck, and autokinesis makes a stationary light wander. The defenses are mechanical: fly the VASI or PAPI and cross-check the altimeter.

Carbon monoxide

Carbon monoxide is colorless, odorless and produced by every internal combustion engine; in a light airplane it arrives through a cracked exhaust feeding the cabin heater, which makes it a winter problem. It binds to hemoglobin over 200 times more readily than oxygen, taking your blood out of service and giving you hypemic hypoxia. Expect headache, blurred vision, dizziness, drowsiness and weakness. It can be there with no smell, so carry a detector. If you suspect it: heater off, vents open, land.

Stress, fatigue and dehydration

Stress is the body's response to demand. Acute stress is short-term and a healthy person copes with it. Chronic stress is an unrelenting load from outside the cockpit that exceeds your ability to cope, and performance falls sharply — a do-not-fly and a see-a-physician. You can also decline to manufacture it: overflying a fuel stop and pressing into marginal weather are self-inflicted.

Fatigue appears in accident reports more than almost anything else here. It degrades attention, impairs coordination and slows communication. Skill fatigue is the version that shows in the airplane: your timing goes slightly out so nothing is smooth, and attention narrows to the center of your vision. Acute fatigue is treated by rest, chronic fatigue by a physician, and dehydration feeds straight into both — the PHAK's guide is two to four quarts of water a day.

Alcohol, drugs and your medical

14 CFR 91.17 sets the floor, and it is a section to quote rather than paraphrase, because each clause is independent: no acting as a crewmember within 8 hours of consuming any alcoholic beverage, none while under the influence of alcohol, none with 0.04 percent by weight or more alcohol in the blood, and none while using any drug that affects your faculties in a way contrary to safety. That is a legal minimum, not a plan: 12 to 24 hours is honest, and a hangover still counts. Alcohol damages judgment, coordination, memory and vision, and altitude multiplies it.

14 CFR 61.53 prohibits acting as pilot in command, or in any other capacity as a required pilot flight crewmember, while a known medical condition or medication would keep you from meeting the requirements of your medical certificate. Over-the-counter medication counts, and a drug's ground effect is not its airborne effect.

The requirement to hold a certificate at all is 14 CFR 61.23, and 14 CFR Part 67 holds the medical standards. The mandatory disqualifying conditions are in the class-by-class subparts of Part 67 — 67.103 through 67.113 for first class, 67.203 through 67.213 for second, 67.303 through 67.313 for third — and they are the sections to read for angina pectoris, cardiac valve replacement, bipolar disorder and the rest. 14 CFR 67.401 is a different provision: special issuance, covering Authorizations for Special Issuance and Statements of Demonstrated Ability, which is why a disqualifying condition is not automatically the end of flying. The CFR is the authority and it changes, so never take a medical, currency or endorsement requirement as settled from a lesson page — including this one — without reading the current section. Take specifics to an AME.

Nitrogen after diving

Diving loads the body with dissolved nitrogen, and climbing too soon releases it as bubbles in the joints and blood. AIM 8-1-2(d) gives the recommended waits, and the paragraph is short enough to read in full: for flight up to 8,000 feet MSL, 12 hours after a dive that needed no controlled ascent and 24 hours after one that did; above 8,000 feet MSL, 24 hours after any dive. If symptoms appear in flight, get on oxygen, descend and land, and do not try to work the pain out of the joint.

Deciding, before and during

All of this is only useful if something makes you check, which is what I'M SAFE is for — Illness, Medication, Stress, Alcohol, Fatigue, Emotion. That last letter is the AIM's, in AIM 8-1-1, and it means the concrete things the paragraph names: a serious argument, a death in the family, a divorce, a job lost. PHAK-lineage material expands the same E as Eating, which is worth running too. Either way, run it before every flight, with the weight you give fuel.

Airborne, the failures are about attention. Aeronautical decision making runs on task prioritization: fly the airplane, then decide, then talk. Single-pilot resource management extends it to everything available — the automation, the chart, ATC.

Two biases do the rest. Confirmation bias is noticing only the evidence that supports the decision you already made; expectation bias is hearing the clearance you expected instead of the one issued. Both are treated by looking for what would prove you wrong. The five hazardous attitudes — anti-authority, impulsivity, invulnerability, macho and resignation — are the same problem with names attached.

Where you meet it next

On a checkride this is oral material: name the four types of hypoxia, separate it from hyperventilation, say which sections govern alcohol and medical deficiency, say how long you wait after drinking or diving, and explain how you decide you are fit.

In the airplane it shows up where it kills people: a night approach into an unfamiliar or unlit airport, where the visual illusions wait, and the first minutes after an inadvertent entry into cloud, where the vestibular ones do. Both are demonstrated with an instructor, deliberately, before they happen to you.

The rest of the ground school assumes a pilot fit to use it. Night Operations takes the visual illusions onto a real approach and a real traffic pattern. Supplemental Oxygen and Cabin Pressurization pick hypoxia back up as equipment rather than physiology. Visual Scanning and Collision Avoidance is the same pair of eyes on a different problem. And Teaching Risk Management and Accident Prevention takes the hazardous attitudes and the two biases from a checklist you run on yourself to something you teach someone else to run.