9.1 Physiology, Fatigue & Fitness to Fly

9.1 Physiology, Fatigue & Fitness to Fly

Quick Answer: Under CAR 901.19, crew must be fit for the operation. Vision and scanning enable VLOS; hearing, orientation, sleep, heat/cold, noise, CO, medications, alcohol, and drugs all affect fitness. Run IMSAFE (Illness, Medication, Stress, Alcohol, Fatigue, Emotion/Eating) before every flight. Impairment = no fly—client pressure does not override physiology.

Human factors account for a large share of aviation incidents because aircraft systems can be serviceable while the human is not. For Advanced RPAS, the pilot and any visual observer are the primary see-and-avoid system. A declared multirotor in controlled airspace is still unsafe if the pilot is exhausted, medicated into drowsiness, or viewing the world through carbon-monoxide haze from a running vehicle used as a ground control station (GCS).

CAR 901.19 — Fitness of crew members

CAR 901.19 requires that crew members be fit for their duties. In exam and operational terms:

• Fitness is personal and situational—you can be fit yesterday and unfit today.
• Fitness covers physical, physiological, and cognitive readiness, not only “I am conscious and holding the controller.”
• It applies to the pilot and to other crew who form part of the safety system (notably visual observers).
• If you are not fit, the correct action is do not operate—not “fly carefully,” not “keep it low,” and not “let the VO do the watching while I push through.”

Advanced privileges, paid contracts, and perfect weather do not create an exception to 901.19.

Vision and visual scanning for VLOS

Visual line-of-sight (VLOS) under the general rules is not a map pin or a camera feed alone. It depends on human vision and a scanning technique that finds traffic, obstacles, and aircraft attitude before a conflict becomes unrecoverable.

What vision must support

Scanning discipline

Effective scanning is systematic, not random staring at the aircraft:

1. Divide the sky and site into sectors (overhead, approach paths, horizon, work area).
2. Pause briefly in each sector—eyes need short stops to detect motion.
3. Alternate between own aircraft, traffic scan, and site hazards (people walking into the pad, vehicles, wildlife).
4. Do not fixate on the tablet map or FPV feed at the expense of unaided eyes (see Section 9.2 on channelized attention).
5. When a visual observer is used, agree who owns which sectors so both people do not scan the same slice while ignoring another.

Corrective lenses, sunglasses appropriate to glare (without destroying contrast for traffic), and protection from dust/wind that causes tearing all support VLOS. Untreated visual problems, severe glare without mitigation, or “I can just watch the screen” culture undermine the legal and safety basis of VLOS operations.

Hearing

Hearing is often undervalued in RPAS because the pilot is on the ground, but it remains a safety channel:

• Radio calls from ATC, FSS/FIC, crew, or other aircraft on common frequencies
• Verbal traffic calls from a visual observer (“traffic left high, moving right”)
• Site sounds: approaching vehicles, people, livestock, construction equipment
• Aircraft or GCS audio alerts (link-loss tones, low-battery warnings, app chimes)

Hearing protection against prop/rotor and generator noise is useful, but total isolation (sealed headphones with entertainment audio) can block critical calls. Balance protection with the ability to hear crew and environment. Temporary threshold shift after loud sites, ear infections, or heavy congestion can reduce radio comprehension—treat significant hearing impairment as a fitness issue for radio-dependent or multi-crew flights.

Orientation, disorientation, and GCS illusions

Unlike manned pilots, RPAS pilots usually remain earth-referenced, but disorientation still occurs:

Parallax and relative-motion illusions at the GCS

When you stand beside a control station and the aircraft is hundreds of metres away:

• Small angular motions can hide large physical displacements.
• Background features (moving clouds, traffic on a road behind the aircraft) create false motion cues.
• Against a uniform sky or snow, attitude (nose high/low, bank) is hard to judge without a clear silhouette.
• Telemetry map orientation (north-up vs track-up) can conflict with what your eyes see, causing a control reversal risk if you “fly the map” while looking at the sky.

Other orientation traps

• Sun in the eyes — temporary loss of the aircraft against glare.
• Night depth compression — distances and closure rates misjudged.
• FPV immersion — strong vection and lean sensations while the body is still; transitioning eyes back to the real sky takes seconds you may not have in a traffic conflict.
• Vestibular mismatch after spinning on a boat/vehicle used as a platform — residual dizziness impairs fine control.

Mitigations: maintain true VLOS when required, use a VO for busy sites, brief map/aircraft reference frames, and refuse flight when visual acquisition of the aircraft cannot be maintained reliably.

Body rhythms, sleep, and fatigue

Humans are circadian organisms. Performance dips in the early morning hours, after long wakefulness, and during the post-lunch trough. RPAS work often includes pre-dawn thermography, long mapping grids, or multi-site days that create sleep debt.

Fatigue effects relevant to drone ops

• Slower reaction to traffic and link-loss events
• Tunnel vision and poor scanning
• Acceptance of higher risk (“just one more battery”)
• Memory lapses on checklists and authorizations
• Irritability that damages CRM with observers and clients

Sleep is the primary recovery tool. Caffeine can mask sleepiness briefly but does not replace sleep and can degrade later rest. Chronic partial sleep restriction (five to six hours per night for several nights) can impair performance similarly to being legally intoxicated—even if you subjectively feel “okay.”

Operational rules of thumb:

• Plan duty days with real rest, not only hotel booking.
• After overnight travel or shift work, treat the first sortie as higher risk or delay.
• If you catch yourself microsleeping at the GCS, land and stop—that is impairment under 901.19 logic.

Anaesthetics, medications, alcohol, and drugs

Anaesthetics and medical procedures

Local, regional, or general anaesthetics and sedating dental/medical procedures can leave residual effects: drowsiness, slowed cognition, impaired coordination. Follow clinician guidance and conservative grounding periods. “The procedure was minor” is not a fitness determination if you still feel foggy.

Prescribed and OTC medications

Many common medications impair aviation-relevant performance:

Rule for the exam and field: if a medication’s label warns against driving or operating machinery, assume it is incompatible with acting as pilot or visual observer until a competent medical source clears you and you feel fully normal. Prescribed status does not automatically mean “safe to fly.” Non-sedating alternatives and timing strategies are medical decisions—not client decisions.

Alcohol and recreational drugs

Alcohol degrades judgment, vision, and coordination. Residual hangover impairment can persist after blood alcohol has fallen. Recreational drugs and misuse of prescriptions are incompatible with crew duty. Substance abuse is both a fitness failure and a professional integrity failure. Advanced operations near people, in controlled airspace, or with multi-crew EVLOS leave no margin for chemical impairment.

Impairment = no fly. There is no “short hop exception.”

Heat, cold, noise, and carbon monoxide

Heat and cold

Hypothermia and heat illness both produce poor decisions before total collapse. Monitor crew, not only aircraft batteries.

Noise

Generators, multirotor prop wash, and industrial sites create continuous noise that raises fatigue and can mask radio calls. Use appropriate hearing protection that still allows critical communications, and rotate VO/pilot roles when noise load is high on long jobs.

Carbon monoxide (CO) from vehicle GCS setups

A classic RPAS trap: running a vehicle for heat, AC, or power while the pilot sits in or near the cabin with a laptop GCS. Carbon monoxide is colourless and odourless. Early symptoms (headache, nausea, confusion, visual disturbance) look like “I am just tired,” which is exactly when you should not be flying.

Controls:

• Prefer external power and ventilated setups.
• Never run an engine in an enclosed space for “just a few minutes.”
• If anyone has CO-like symptoms, stop operations, get fresh air, seek medical care, and treat the event as a serious occurrence—not a joke about “garage flu.”

IMSAFE adapted for RPAS

Use IMSAFE as a personal pre-flight checklist every time—solo or multi-crew:

Any significant “yes” is a no-go or a hard delay until the factor is resolved. Logging a brief personal fitness call in professional ops culture is a strength, not a weakness.

Integrating physiology with the rest of the flight

Fitness sits beside serviceability (Chapter 8) and site survey (later ops chapters):

1. Aircraft serviceable (901.29 themes).
2. Crew fit (901.19).
3. Environment acceptable (weather, airspace, people distances).
4. Plan and briefings complete.

If step 2 fails, stop—do not compensate with more automation or a lower altitude.

Common exam traps for Section 9.1

• Treating Advanced certificate as a waiver of personal fitness
• Assuming VLOS is satisfied by telemetry alone when vision is degraded
• Ignoring hangover, OTC antihistamines, or post-procedure fog
• Running a vehicle GCS with CO risk because “it is cold outside”
• Flying through fatigue because the client is on site
• Applying IMSAFE only after an incident instead of before every flight

Master 901.19, vision/scan discipline, environmental stressors, medication/alcohol rules, and IMSAFE, and human-physiology questions become structured go/no-go decisions rather than vague “be careful” advice.