5.4 Physiological Factors Affecting Pilots

Human Physiology and the Remote Pilot

A Remote PIC never leaves the ground, yet human physiology still limits performance — vision, fatigue, stress, heat, and impairment all degrade the ability to maintain visual line of sight and make sound decisions. The exam tests both the regulatory limits and the practical vision facts.

Vision and Visual Scanning

Maintaining visual line of sight (VLOS) depends on usable vision, and several effects work against you:

• Glare from bright sun can wash out the aircraft. Polarized sunglasses cut glare but can dim a controller's liquid-crystal display, so weigh the trade-off.
• Dark adaptation for night flight takes about 20-30 minutes, and a single glance at a bright phone or vehicle headlight can reset it. Protect your night vision before and during a dusk-to-dark operation.
• Empty-field myopia is the most-tested vision trap: facing a clear, featureless sky, the relaxed eye focuses at a resting distance of only 10-30 feet, so a distant aircraft simply is not in focus. Counteract it by periodically focusing on the horizon or a far object to "reset" your eyes.

Use a deliberate scanning pattern rather than staring at the drone. Divide the sky into sectors, pause briefly in each to let the eye detect motion, and have the VO scan different sectors than the PIC for full coverage.

Fatigue

Fatigue slows reaction time, narrows attention (tunneling), erodes judgment, and increases risk-taking. Mitigate it with 7-8 hours of sleep, breaks on long jobs, hydration and food, and a hard personal rule against flying after being awake 12-15 hours.

Hypoxia (for Context)

Hypoxia is insufficient oxygen reaching the brain and tissues — headache, dizziness, euphoria, tunnel or blurred vision, and impaired judgment. It is rarely a factor at ground level, but a crew operating from a high mountain site (for example, above 10,000 feet) can feel its early effects.

Stress

Stress narrows attention to tunnel vision, raises error rates, and frays crew communication, often with physical signs (racing heart, sweating, muscle tension). Screen for it with IMSAFE, set more conservative personal minimums on a stressful day, and rehearse emergency procedures so they run on autopilot when pressure spikes.

Heat-Related Illness

Heat stroke is a life-threatening emergency, not a "take a break" situation — recognizing the shift from heavy sweating to hot, dry skin and confusion is the key distinction.

Alcohol and Drugs

The regulatory limits below mirror the manned-aircraft standard and are exam favorites:

Beyond the timing rule, the FAA may request a drug or alcohol test following an accident, and refusing the test, or testing at or above the limit, is itself grounds for certificate action. The safe practice is the manned-aviation mindset: when in doubt about a medication's effect, wait until you are confident it has cleared your system.

Spatial Disorientation and Vection

A subtler vision hazard for drone pilots flying by First-Person View (FPV) is vection — a false sense of self-motion induced by watching a moving video feed, similar to feeling you are rolling when the car beside you pulls away. Staring into an immersive FPV display while standing still can produce dizziness, nausea, and brief disorientation. The defenses are to keep a visual observer maintaining unaided line of sight on the aircraft, to glance up from the screen periodically to re-anchor on the real horizon, and to stop if symptoms appear.

Flying purely by FPV without a visual observer who keeps the aircraft in unaided sight is generally not permitted under Part 107 unless a waiver authorizes it.

Carbon Monoxide and Noise

Ground crews working near running generators (for charging) or vehicles risk carbon monoxide (CO) exposure — an odorless gas whose early symptoms (headache, drowsiness, confusion) mimic fatigue and degrade judgment before the pilot realizes anything is wrong. Keep generators downwind and well away from the control station. Prolonged exposure to loud equipment can also cause temporary hearing loss that hampers crew communication; hearing protection on a noisy site is a legitimate safety measure.

For the Exam: Lock in the 8-hour bottle-to-throttle rule and the 0.04% Blood Alcohol Concentration limit, the 20-30 minute dark-adaptation window, and empty-field myopia's 10-30 foot resting focus. Fatigue and stress are impairments the PIC must self-screen with IMSAFE before every flight.