The pilot is the centre of the system. Before we look at stressors, we look at the evidence: what actually causes accidents.
A1Accident dataFAA · NTSB · AOPA
A2HFACSerror types
A3SHELLsystem interfaces
A4IMSAFEfitness for flight
A5Sleepcircadian rhythm
A1 · Accident data analysis
The human factor in numbers
0%
of fatal GA accidents relate directly to human factors
FAA GA Safety Fact Sheet, 2012
0%
of 2023 U.S. non-commercial fixed-wing accidents were pilot-related (651 of 929)
AOPA ASI McSpadden Report, 2023 data
#1
Loss of control in flight — the leading cause of fatal GA accidents
FAA Fact Sheet · AOPA 2023
0/10
VFR into IMC accidents in 2023 — every one was fatal
AOPA ASI McSpadden Report, 2023 data
2023 U.S. non-commercial fixed-wing accidents by major cause (n = 929)
Pilot-related651
Mechanical187
Other / unknown91
Sources: FAA Fact Sheet “General Aviation Safety” (June 2012) · AOPA Air Safety Institute, Richard G. McSpadden Report (2023 accidents, published Nov 2025)
A2 · Human Factors Analysis & Classification System
Which errors crash airplanes?
% of GA accidents with ≥ 1 error of this type · 1990–2000
Skill-based errors79.2%
Decision errors29.7%
Violations13.7%
Perceptual errors5.7%
Skill-based errors — basic stick-and-rudder and attention failures — dominate. Categories overlap: one accident can contain several error types.
Top skill-based
Directional control 11.8%
Airspeed maintenance 10.6%
Stall / spin 7.8%
Top decision
In-flight planning 18.3%
Ground planning 8.9%
Fuel management 8.7%
Top violations
VFR flight into IMC 15.5%
Not following procedures 10.9%
Known aircraft deficiencies 9.9%
Source: Wiegmann, Shappell et al., “Human Error and General Aviation Accidents: A Comprehensive, Fine-Grained Analysis Using HFACS”, FAA Office of Aerospace Medicine, DOT/FAA/AM-05/24 (2005) — NTSB data 1990–2000
2Procedural lapse — speed brake not stowed, landing gear not extended
4Environment only — insufficient lift, no pilot error named
The 4 fatal accidents
Stall while manoeuvring for landing — critical AoA exceeded
Stall/spin turning back after an early tow release — critical AoA
Loss of control near a ridge in downdrafts — too low to recover
Low-altitude tow release, stall returning to runway — critical AoA
4 of 4 = loss of control in flight. 6 accidents in total cite exceeding the critical angle of attack.
Instructor’s classification of the 30 NTSB probable causes (Feb 2020 – Jul 2022) listed in the FAA Glider Flying Handbook, FAA-H-8083-13B, ch. 13. Injury: 4 fatal · 9 serious · 5 minor · 12 none.
A3 · System view
The SHELL model
Centre of the model
Liveware — the pilot
Example interface failure
Accidents usually happen at the interfaces between components, not inside one of them. · ICAO Doc 9683 Human Factors Training Manual
A4 · Fitness for flight
IMSAFE — before every flight
Ask yourself
Rule / reference
A medical certificate shows fitness on the day of the exam only — self-grounding is the pilot’s right and duty. · FAA-H-8083-25 ch. 17 · CASR Part 67 (medical) · CASR 91.17
A5 · Sleep & circadian rhythm
The 24-hour clock inside you
Relative alertness across 24 h (illustrative pattern)
Sleep need
Most adults need 7–9 hours per night.
Sleep debt
Accumulates and is not repaid by one long night.
Jet lag & shift work
Shifts the rhythm; adaptation is roughly one hour per day.
Strategy
Consistent sleep schedule, 20–30 min nap, limit afternoon caffeine, track your sleep.
Body temperature, heart rate and alertness rise and fall daily (FAA-H-8083-13B Fig. 13-3). Curve is a conceptual illustration, not measured data.
Quiz · section A
Section A quiz
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B
Some problems steal the judgment you need to notice them.
Section B
Respiration & pressure
The atmosphere thins as you climb, your body reacts to pressure and acceleration — learn the symptoms before they impair you.
B1Atmospherepartial pressure
B2Hypoxia4 types · TUC
B3Oxygen91.211 · PRICE
B4HyperventilationCO₂ balance
B5Pressure & Gear · diving · +Gz
B1 · Atmosphere
Pressure falls, 21% stays
One breath of air
O₂N₂ & other
Total pressure100%
O₂ share of the air21%
O₂ “felt” vs sea level21%
Standard-atmosphere pressure ratios (approx.). Partial pressure of O₂ = 21% × total pressure.
TUC values: FAA-H-8083-13B Figure 13-5 (seated, healthy individual). Exertion, smoking, fatigue, alcohol and illness shorten TUC. Night vision can degrade from about 5,000 ft (AIM 8-1-2).
12 hafter dives that did not need decompression stops
24 hafter dives that did need decompression stops (controlled ascent)
If symptoms appear in flight
Joint pain (“the bends”), itching, tingling, chest pain, confusion → 100% oxygen, descend, land, tell ATC; treatment may need a hyperbaric (recompression) chamber.
B5 · Carbon monoxide — silent hypemic hypoxia
Why CO wins the seat
O₂CO — binds ≈ 200–250× more strongly, releases slowly
Seats taken by CO (COHb)
0%
Suspect CO? Act at once
Cabin heat OFF
Fresh-air vents OPEN
Oxygen if available
Land as soon as possible · tell ATC
Prevent
Inspect the exhaust/heater shroud, fit a CO detector. Smokers already carry several % COHb before flight.
FAA-H-8083-25 ch. 17 · FAA pilot safety brochure “Carbon Monoxide: A Deadly Menace”. Percentages are approximate and individual tolerance varies — symptoms are unreliable; trust the detector.
Under +Gz blood pools in the legs and abdomen; the heart pumps against the load and pressure at eye level drops. The retina is affected before the brain.
Protection
AGSM: tense legs & abdomen, short breaths
G-suit and upright posture
Hydration, nutrition, fitness, recency
Fatigue & alcohol lower tolerance
Approximate, unprotected values; individuals vary. −Gz (negative): red-out and headache, far lower tolerance.
Quiz · section B
Section B quiz
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C
Your senses evolved on the ground — not in a cockpit.
Section C
Vision & orientation
How the eye works, why it misses traffic, and how the inner ear and visual illusions lead pilots into loss of control.
C1The eyerods · cones
C2Scanningsee & avoid
C3Vestibularillusions
C4Visual illusionsapproach · night
C5Recoveryspiral · motion sickness
C1 · Anatomy of the eye
From light to image
What it means for a pilot
C1 · Night vision — made simple
Seeing in the dark
Your eye has two “cameras”
Day cameraCones · center of vision · sharp & color · needs light
Night cameraRods · around the center · sees dim light & movement · no color, no detail
3 rules for night flying
Look 5–10° beside a dim light — the center of your eye is blind at night.
Keep the eyes moving; a stared-at light fades or seems to wander.
Protect 30 min of adaptation: dim red/low white light; one bright flash resets it.
Dark adaptation
010 min20 min30 min
Rods reach full sensitivity after about 30 minutes in darkness.
FAA-H-8083-25 ch. 17 (Vision in flight) · AIM 8-1-6. Navigation lights: red on the left wingtip, green on the right, white on the tail.
C2 · See and avoid
Scan, spot, avoid
ATC“Traffic, two o’clock, three miles, opposite direction, altitude indicates four thousand five hundred.”You“Looking.” … “Traffic in sight.”
Why pilots miss traffic
Blocked view — windshield posts, wings, the sun
Empty-field myopia — on a blank sky the eyes focus 1–2 m away
Head-down — tablets, charts, radios
Tiny target — a collision threat barely grows until the last seconds
FAA AC 90-48 · reaction time
From first seeing an aircraft to your aircraft actually turning takes about 12.5 seconds. At a 250 kt closing speed that is almost 1 nm.
C3 · Spatial disorientation — inside the inner ear
When the inner ear lies
Semicircular canal — senses rotation
Aircraft is—
Inner ear tells the brain—
Actual
Feels like
Three canals (roll, pitch, yaw) sense angular acceleration; a constant turn is not felt after ≈ 10–20 s. Rotation below ≈ 2°/s is not sensed at all. · FAA-H-8083-25 ch. 17 · FAA-H-8083-15B ch. 3
A VFR private pilot must never continue VFR into IMC. Set a decision point, turn back 180° while you still have visual references, and ask ATC for help.
C5 · Motion sickness
Sensory conflict
Eyes“The cabin is still.”
≠
Inner ear“We are turning and bumping.”
→
BrainNausea · pallor · sweating · dizziness
Triggers
Turbulence & aggressive manoeuvres
Anxiety, lack of sleep
Fuel smell, hot stuffy cabin
Too full or too hungry
Countermeasures
Fresh air — open the vents
Look at the outside horizon; limit head movement
Stop manoeuvring, fly smoothly
Descend or land if it does not improve
Coping with disorientation
Believe the instruments
Cross-check attitude, altimeter, VSI, heading
Control attitude: wings level, pitch, then power
Minimise head movement
Ask ATC for help
Anti-motion-sickness drugs often cause drowsiness — use only with an aviation medical examiner’s approval. · FAA-H-8083-25 ch. 17
Quiz · section C
Section C quiz
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D
Most errors come from a tired or overloaded mind — not a lack of skill.
Section D
Mental performance
What happens inside the pilot’s head: fatigue, stress, attention and the limits of memory.
D1Fatigueacute · chronic
D2StressYerkes-Dodson
D3Workloadattention traps
D4Informationprocessing model
D5Countermeasureschecklists · readback
D1 · Fatigue
Hours awake = alcohol?
Hours awake → equivalent impairment
0.05%0.10%
≈ normalalertness after a normal morning
Williamson & Feyer (2000), Occupational and Environmental Medicine: 17–19 h awake ≈ BAC 0.05%; longer ≈ 0.1%.
Acute fatigue
Long duty day, short night, hard physical or mental work — relieved by rest.
Chronic fatigue
Accumulated sleep debt and prolonged stress — needs medical attention; stop flying until resolved.
Warning signs
Slow reactionsMissed radio callsFixationMisreading instrumentsIrritabilityMicro-sleeps
Countermeasures
Regular adequate sleep, track sleep hours, a short nap, delay the flight. Caffeine works briefly but can worsen fatigue long-term (FAA-H-8083-13B).
D2 · Stress
The Yerkes-Dodson curve
Stressors
Environmental: noise, heat, vibration
Physiological: fatigue, illness, hunger
Psychological: time pressure, checkrides, personal problems
Managing stress
Thorough preparation & briefing
Prioritize: aviate, navigate, communicate
Steady breathing, speak slowly
Ask for help early
Conceptual relationship (Yerkes & Dodson). Chronic stress lowers the whole curve — consider raising personal minimums.
D3 · Workload & attention
When the bucket overflows
Relative workload by phase of flight (illustrative)
Preflight
Taxi
Takeoff
Climb
Cruise
Descent
Approach
Landing
Plan and brief during low-workload phases (cruise) so the high-workload phases are rehearsed, not improvised.
Tunnel visionFixating on one problem and forgetting to fly the aircraft.
ComplacencyRoutine breeds a false sense of security — checks get skipped.
D4 · Information processing — inside the nervous system
From stimulus to action
0.1 ssee object
1.0 srecognize aircraft
5.0 saware of collision course
4.0 sdecide: turn left or right
0.4 smuscle reaction
2.0 saircraft lag
FAA AC 90-48 (Pilots’ Role in Collision Avoidance): ≈ 12.5 s from seeing traffic to the aircraft responding.
Inside one nerve cell
In the cockpit
Quiz · section D
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E
Errors are normal. Managing them is airmanship.
Section E
Decisions & error
From understanding the problem to managing it: error types, the error chain, hazardous attitudes, ADM, risk and TEM.
E1Error typesslip · lapse · mistake
E2Error chainSwiss cheese
E3Attitudes5 hazardous
E4ADM & riskDECIDE · PAVE
E5TEMthreat · error · UAS
E1 · Types of error
Not all errors are equal
Unsafe act
Unintentional — errorIntentional
Example
Countermeasure
In the data
Error cannot be eliminated — it must be managed. FAA-H-8083-13B separates unintentional errors (tolerance, judgment, knowledge) from intentional deviations, which signal a deeper lack of concern for safety.
E2 · Error chain
Holes that line up
FAA-H-8083-13B: decision chains
Slow oxygen leak“Perfect soaring day — I won’t need oxygen.”
High winds forecast later“I can be back before the wind changes.”
Aircraft / radio batteries low“Only a short flight, so I’ll go.”
Fix the leak, respect the forecast, charge the batteries — one broken link changes the outcome. The pilot is the last layer of defence.
James Reason’s model as used in HFACS: organizational influences → unsafe supervision → preconditions → unsafe acts.
E3 · Hazardous attitudes (FAA)
Say the antidote
Complacency
False sense of security — “done this a million times”. Prepare, examine hazards, demand excellence.
Indiscipline
Shortcuts and rule-bending. Set personal minimums stricter than the regulations.
Overconfidence
Not knowing your limits in an unfamiliar aircraft or environment. Stay current and proficient.
FAA-H-8083-25 ch. 2 · FAA-H-8083-13B ch. 13 · AC 60-22. Military pilots are often most exposed to macho and invulnerability.
The FAA’s recommended loop for every phase: perceive hazards, process their level of risk, perform risk management — then start the loop again as the flight progresses.
Use with a Flight Risk Assessment Tool (FRAT) and written personal minimums (FAA-H-8083-2).
E4 · Risk assessment
Likelihood × severity
LIKELIHOOD
NegligibleMinorMajorCatastrophic
SEVERITY
Red — unacceptable: cancel or change the planOrange — mitigate and get instructor approvalYellow — accept with mitigationGreen — accept, stay alert
E5 · Threat and error management
Trap it early
ThreatOutside the pilot’s control
Weather, ATC, terrain, traffic, time pressure
→
ErrorPilot action or inaction
Slip, lapse, mistake, violation
→
Undesired aircraft stateReduced safety margin
Altitude deviation, loss of control, CFIT path
Threat
Error
Undesired state
Countermeasure
PlanBriefing, alternates, fuel & weather margins
ExecuteChecklists, monitoring, cross-check, clear communication
Review & modifyPeriodic evaluation, turn back, ask for help
E · Case study
What is your decision?
Scenario
Lt. A has just finished a night duty and slept only 4 hours. This afternoon he must fly a trainer solo to another base. He has a mild cold, the route forecast is marginal VFR over hills, and his commander is waiting for the aircraft at the destination.
Walk through the four questions — tap each one.
Quiz · section E
Section E quiz
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Closing · review
How was the lesson?
Your rating helps the instructor improve. Give 1–5 stars for each aspect.
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Closing
Know your limits
A
≈ 80% of fatal GA accidents involve human factors. Run IMSAFE every flight; self-ground when in doubt.
B
Hypoxia hides behind euphoria — oxygen & descend. Know your TUC, CASR 91.211 and PRICE.
C
Scan 10° sectors; at night look off-center. In IMC, believe the instruments.
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