Aviation Human Factors and Physiological Illusions Study Guide

The Physiology and Function of Human Vision in Flight

The Eye as a Camera Analogy: * The eye functions similarly to a camera. Light enters through a lens in the front and hits a sensor in the back. * In a camera, this sensor is film (in old photography) or a digital sensor that converts light into a file. * In the human eye, the light is captured by tiny receptors called photoreceptors, which convert light into signals the brain can interpret.
Photoreceptors: Rods and Cones: * Cones: * Primarily located in the back of the eye in an area used for central vision called the fovea (referred to by the speaker as "a vision" area). * They are "color specialists" and handle detail and color perception. * They adapt to darkness relatively quickly, reaching full sensitivity within a few minutes, but their peak sensitivity is limited. * Rods: * Located mostly on the sides of the eye, handling peripheral vision. * Incredibly sensitive to light, being $10,000$ times more sensitive than cones. * They cannot detect color. * They take significantly longer to adapt to the dark, requiring approximately $20$ to $25$ minutes to reach peak sensitivity.
Signal Transmission and the Blind Spot: * Information travels from photoreceptors to the brain via the optic nerve, which acts as a cable running from the back of the eye. * The Blind Spot: At the point where the optic nerve connects to the eye, there are no rods or cones. This creates a small area that captures no data. * Blind Spot Experiment: * Draw a small circle (dot) on one side of a paper and a cross on the other. * Hold the paper so the cross is directly in front of the eye and the dot is in the peripheral. * Adjust the distance of the paper (usually about a certain distance from the face, not too close); at a specific point, the dot disappears because it falls into the blind spot. * Pilot Implication: If another aircraft in the distance is positioned exactly in that blind spot, it will be invisible to the pilot.

Visual and Optical Illusions in Aviation

False Horizon: * Occurs on hazy days, over water, or when flying over sloped cloud clusters. * Personal Anecdote: A student pilot in Florida flying eastbound on a hazy day mistook a sloped cluster of clouds for the horizon. He entered a gentle turn and went off course. Even after realizing the mistake, it was difficult to "convince the brain" that the aircraft was level because it felt wrong. * Nighttime False Horizons: Bright stars or city lights in a straight line can be mistaken for the horizon.
Autokinesis: * Refers to the illusion where a small, stationary light in the dark appears to move if stared at for too long. * Personal Anecdote: The speaker experienced this while flying drones at night; the drone's light appeared to move even though the drone was verified to be stationary. * Consequence: Pilots may make unnecessary or dangerous flight adjustments based on the perceived movement.
Runway Width Illusions: * Narrow Runway: Makes the pilot feel they are too high. The natural reaction is to fly a lower-than-normal approach. * Wide Runway: Makes the pilot feel they are too low. The natural reaction is to fly higher, which can lead to overshooting or running out of runway.
Runway Slope Illusions: * Down-sloping Runway: Appears shorter and wider than normal, causing the pilot to feel lower than they are. This leads to a higher-than-normal approach. * Up-sloping Runway: Appears long and skinny, causing the pilot to feel higher than they are. This leads to a lower-than-normal approach.
Featureless Terrain Illusion: * Occurs over water (at night), dark unpopulated areas, or snow ("blank white canvas"). * It robs the pilot of depth perception and cues. * Personal Anecdote: The speaker flew into Merritt Island in Florida, where the runway extended into a river. At night, with no land reference points around the dark water, depth perception was absent.
Atmospheric Illusions: * Water Refraction: Rain on the windscreen makes the horizon appear lower than it is, creating the illusion that the aircraft is higher than it is. This may tempt the pilot to fly lower. * Haze: Objects (like other aircraft) appear further away than they actually are because their clarity is reduced. This can lead to flying a lower-than-normal approach. * Fog: Entering fog can create an illusion of pitching up. This is related to the somatographic illusion, where forward acceleration or the entrance into fog (losing visual cues) is interpreted by the vestibular system as upward pitch.

Dark Adaptation and Night Scanning

The Adaptation Process: * Cones adapt in a few minutes but have low sensitivity. * Rods are less sensitive than cones for the first $7$ minutes, but then their sensitivity increases dramatically, peaking after $20$ to $25$ minutes. * After approximately $7$ minutes, peripheral vision becomes more useful for spotting objects in low light than central vision.
Protecting Night Vision: * Resetting Adaptation: Exposure to bright light (phones, bright instruments, landing lights of other aircraft) immediately resets dark adaptation to "square one." * Pilot Recommendation: Give the eyes at least $30$ minutes to fully adapt before a night flight. * Practical Tip: Wear sunglasses inside the building before a night flight to prevent bright lights from entering the eyes, though they must be removed on the ramp.
Scanning Techniques: * Do not sweep the eyes across the sky (like watching a tennis match). * Break the sky into segments and move the eyes in $10$ -degree increments. * Maintain each gaze for $2$ to $3$ seconds to catch movement. * Scan from the distance (further out) and work your way inward.

Aeromedical Factors: Motion Sickness, Stress, and Fatigue

Motion Sickness: * Caused by conflicting information between the brain and the body's position (sensory conflict). * Symptoms: Nausea, dizziness, vomiting. * Remedies: Fresh air (vents or storm windows), focusing on the distance/horizon, and avoiding quick head movements. * Warning: Medication like Dramamine is prohibited for pilots as it causes drowsiness.
Stress: * Acute Stress: Short-term, immediate reaction to a specific event. * Chronic Stress: Long-term, from ongoing life situations. It degrades judgment and performance over time.
Fatigue: * Acute Fatigue: Short-term, caused by physical or psychological exertion or mild hypoxia. Remedied by diet and rest. * Chronic Fatigue: Long-term, often rooted in medical or psychological issues. Symptoms include weakness, heart racing, irritability, and headaches. * Crucial Note: Training and experience cannot overcome fatigue; the brain will trick the pilot into thinking they are performing better than they are.

Dehydration, Heat Stroke, and Substance Rules

Dehydration: * Caused by heat, wind (removing moisture), and diuretics (caffeine, coffee, tea, alcohol). * Symptoms: Headache, fatigue, muscle cramps, dizziness. * FAA Recommendation: Drink $2$ to $4$ quarts of water every $24$ hours. In heat, drink $1$ quart per hour. * Thirst Warning: By the time you feel thirsty, you have already lost $2\%$ of your body weight in water.
Heat Stroke: The body's inability to control temperature, often preceded by dehydration.
Alcohol and Drugs: * FAR 91.17 and 91.19: Prohibits flying while under the influence. * 8-Hour Rule: Wait at least $8$ hours after the last drink (minimum); many recommend $12$ hours. * Blood Alcohol Content (BAC): Must be below $0.04$ . * Hangovers: Alcohol impacts the body for up to $16$ hours; flying while hungover is considered under the influence.

Decompression Sickness (DCS) and Diving Rules

Definition: Nitrogen gas bubbles out of the blood and moves to porous areas (skin, spine, lungs, brain, heart) due to a sudden drop in pressure.
Boyle's Law (Bohr's Law): Explains the relationship between gas pressure and volume using the formula: $P_1 V_1 = P_2 V_2$ * If initial pressure ( $P_1$ ) is high and volume ( $V_1$ ) is small (like a sealed Coke can), a drop in pressure ( $P_2$ ) causes the volume of the gas/bubbles ( $V_2$ ) to expand rapidly.
FAA Rules for Flying After Scuba Diving: * Below 8,000 ft: * Wait $12$ hours after a dive not requiring a controlled ascent. * Wait $24$ hours after a dive requiring a controlled ascent. * Above 8,000 ft: Always wait $24$ hours regardless of the type of dive.

Aeronautical Decision Making (ADM) and Risk Management

ADM Definition: A systematic approach to the mental process used by pilots to consistently determine the best course of action.
Statistics: $80\%$ of all aviation accidents are related to human factors; $24\%$ occur during landing and $22\%$ occur during takeoff.
Hazard vs. Risk: * Hazard: A real or perceived condition/event encountered (e.g., an aircraft approaching on a collision course). * Risk: The value or assessment assigned to that hazard based on severity and likelihood.
The Risk Matrix: * Severity: Catastrophic, Critical, Marginal, Negligible. * Likelihood: Probable, Remote, Improbable. * Example: A mid-air collision has a "Catastrophic" severity. If the likelihood is "Probable," the risk is "High."
Checklists for Risk Mitigation: * I'M SAFE: Illness, Medication, Stress, Alcohol, Fatigue, Emotion. * PAVE: Pilot (use I'M SAFE), Aircraft (airworthiness/familiarity), Environment (weather/terrain), External Pressures (passengers/bosses).

Hazardous Attitudes and Antidotes

Anti-authority: "Don't tell me what to do." * Antidote: Follow the rules; they are there for a reason.
Impulsivity: "Do it quickly." * Antidote: Not so fast; think first.
Invulnerability: "It won't happen to me." * Antidote: It could happen to me.
Macho: "I can do it / Hold my beer." * Antidote: Taking chances is foolish.
Resignation: "What's the point? / I can't do anything." * Antidote: I'm not helpless; I can make a difference. (Fly the wreckage to the ground).

Resource Management and Situational Awareness

Crew Resource Management (CRM): Utilizing all available resources (Human, Hardware, Information) to ensure flight success. * Personal Anecdote: A flight school instructor used ground personnel, binoculars, and towers to assess gear failure, enabling a safe landing (despite propeller damage).
Single Pilot Resource Management (SRM): Managing all resources (Task management, Automation management, ADM, Risk management) by oneself.
CFIT (Controlled Flight Into Terrain): When a functional aircraft is flown into the ground due to the pilot's loss of awareness.
Situational Awareness (SA): Accurately perceiving factors affecting the flight (Where am I? What is happening around me?). * SA Destroyers: Fatigue, Stress, and Workload Overload (Fixation). * Eastern Airline Flight 401 (1970s): The crew fixated on a burnt-out landing gear light, allowing the autopilot to disconnect. The plane descended slowly into the Everglades, killing $100$ people.

The 5 Ps and Other Decision Models

The 5 Ps: 1. Plan: The mission, route, weather, and fuel. 2. Plane: Mechanical status, automation, database currency. 3. Pilot: Physical and mental state (I'M SAFE). 4. Passengers: Their needs and schedules (pressure to arrive). * Example: Suggesting a rental car in Dallas to alleviate pressure on the pilot. 5. Programming: Managing avionics and automation.
The DECIDE Model: Detect, Estimate, Choose, Identify, Do, Evaluate.
The 3 Ps (Preferred by the speaker): 1. Perceive: Notice something is happening. 2. Process: Brain evaluates the situation. 3. Perform: Execute the necessary action.

Operational Pitfalls

Peer Pressure: Doing something unsafe because others want you to.
Scud Running: Flying low with low visibility to maintain visual contact with terrain (e.g., Kobe Bryant accident).
Get-there-itis: The obsession with reaching a destination regardless of danger.
VFR into IMC: Visual pilots flying into clouds (e.g., JFK Jr. accident).
Automation Management: Avoiding complacency. Automation is "dumb" and only does what you program. * Tip: Disconnect autopilot in icing conditions to prevent incorrect flight control responses.