Human Factors

PHAK 17-12

• The body’s reaction to stress includes releasing chemical hormones (such as adrenaline) into the blood and increasing metabolism to provide more energy to the muscles

• Examples of stressors include physical stress (noise or vibration), physiological stress (fatigue), and psychological stress (difficult work or personal situations)

Acute

• Acute stress involves an immediate threat that is perceived as danger 

• Triggers a “fight or flight” response in an individual, whether the threat is real or imagined 

• Normally, a healthy person can cope with acute stress and prevent stress overload 

• However, ongoing acute stress can develop into chronic stress

Chronic

• Chronic stress can be defined as a level of stress that presents an intolerable burden, exceeds the ability of an individual to cope, and causes individual performance to fall sharply 

• Unrelenting psychological pressures, such as loneliness, financial worries, and relationship or work problems can produce a cumulative level of stress that exceeds a person’s ability to cope with the situation 

• When stress reaches these levels, performance falls off rapidly

PHAK 17-13

• Effects include degradation of attention and concentration, impaired coordination, and decreased ability to communicate

• Physical fatigue results from sleep loss, exercise, or physical work 

Acute

• Short term and is a normal occurrence in everyday living. It is the kind of tiredness people feel after a period of strenuous effort, excitement, or lack of sleep

• Timing disruption — appearing to perform a task as usual, but the timing of each component is slightly off. This makes the pattern of the operation less smooth because the pilot performs each component as though it were separate, instead of part of an integrated activity

• Disruption of the perceptual field — concentrating attention upon movements or objects in the center of vision and neglecting those in the periphery. This is accompanied by loss of accuracy and smoothness in control movements

• The most important causes of fatigue are hypoxia, physical stress and depletion of physical energy resulting from sustained psychological stress

Chronic

• Extends over a long period of time and is caused by continuous high-stress levels, psychological stress or underlying disease.

• An individual may experience this condition in the form of weakness, tiredness, palpitations of the heart, breathlessness, headaches, irritability, stomach and body aches problems or emotional illness

• Chronic fatigue is not relieved by proper diet and adequate rest and sleep and usually requires treatment by a physician

PHAK 17-14

• Dehydration is the term given to a critical loss of water from the body

• Causes of dehydration are hot flight decks and flight lines, wind, humidity, and diuretic drinks—coffee, tea, alcohol, and caffeinated soft drinks

• Some common signs of dehydration are headache, fatigue, cramps, sleepiness, and dizziness

• The first noticeable effect of dehydration is fatigue, which in turn makes top physical and mental performance difficult, if not impossible

• Flying for long periods in hot summer temperatures or at high altitudes increases the susceptibility to dehydration because these conditions tend to increase the rate of water loss from the body

• The body normally absorbs water at a rate of 1.2 to 1.5 quarts per hour. Individuals should drink one quart per hour for severe heat stress conditions or one pint per hour for moderate stress conditions

FAR 91.17

PHAK 17-15

FAA Alcohol & Flying Brochure

Alcohol

• Even in small amounts, alcohol can impair judgment, decrease sense of responsibility, affect coordination, constrict visual field, diminish memory, reduce reasoning ability, and lower attention span

• The bloodstream absorbs about 80 to 90 percent of the alcohol in a drink within 30 minutes when ingested on an empty stomach

• The body requires about 3 hours to rid itself of all the alcohol contained in one mixed drink or one beer

• While experiencing a hangover, a pilot is still considered under the influence of alcohol

• FAR 91.17 requires that blood alcohol level be less than .04 percent and that 8 hours pass between drinking alcohol and piloting an aircraft

Drugs

• Even at typical general aviation altitudes, the changes in concentrations of atmospheric gases in the blood can enhance the effects of seemingly innocuous drugs that can result in impaired judgment, decision-making, and performance

• Some of the most commonly used OTC drugs, antihistamines and decongestants, have the potential to cause noticeable adverse side effects, including drowsiness and cognitive deficits

• Over-the-counter analgesics, such as acetylsalicylic acid (Aspirin), acetaminophen (Tylenol), and ibuprofen (Advil), have few side effects when taken in the correct dosage

• Flying is almost always precluded while using prescription analgesics, since these drugs are known to cause side effects, such as mental confusion, dizziness, headaches, nausea, and vision problems

• For any new medication, OTC or prescribed, you should wait at least 48 hours after the first dose before flying to determine you do not have any adverse side effects that would make it unsafe to operate an aircraft

PHAK 17-12

• Caused by the brain receiving conflicting messages about the state of the body

• Symptoms of motion sickness include general discomfort, nausea, dizziness, paleness, sweating, and vomiting

• If symptoms of motion sickness are experienced, opening fresh air vents, focusing on objects outside the airplane, and avoiding unnecessary head movements may help alleviate some of the discomfort

PHAK 17-4

• Excessive rate and depth of respiration leading to abnormal loss of carbon dioxide from the blood

• Hyperventilation can lead to unconsciousness due to the respiratory system’s overriding mechanism to regain control of breathing

• Symptoms include lightheaded or dizziness, unconsciousness, visual impairment, tingling or temperature sensations and muscle spasms

• Breathing normally is both the best prevention and the best cure for hyperventilation

• In addition to slowing the breathing rate, breathing into a paper bag or talking aloud helps to overcome hyperventilation

PHAK 17-3

Hypoxic

• Insufficient supply of oxygen to the brain due to the reduction in partial pressure at high altitude

• Lungs can't transfer oxygen to blood, brain doesn't recieve enough oxygen

• Dry ice sublimates into large quantities of CO2 gas, which can rapidly displace oxygen-containing air and potentially cause hypoxia via carbon dioxide intoxication

Hypemic

• Blood is not able to take up and transport a sufficient amount of oxygen to the cells in the body

• CO poisoning leaves hemoglobin, the actual blood molecule that transports oxygen, chemically unable to bind oxygen molecules

• Reduced blood volume, blood donation and blood diseases are also factors

Stagnant

• Oxygen-rich blood in the lungs is not circulating to the tissues that need it

• Causes can include shock, the heart failing to pump blood effectively, a constricted artery, excessive gravity acceleration (Gs), and cold temperatures 

Histotoxic

• The inability of the cells to effectively use oxygen

• Impairment of cellular respiration can be caused by alcohol and other drugs, such as narcotics and poisons

Effects of Hypoxia

• Reduction in mental function while flying which can result in life-threatening errors

• Headache, drowsiness, dizziness, lightheadedness, impaired judgment, decreased reaction time, euphoria, visual impairment, cyanosis and numbness in finger and toes

PHAK 17-12

• Colorless and odorless gas produced by all internal combustion engines

• By attaching itself to the hemoglobin in the blood about 200 times more easily than oxygen, CO prevents the hemoglobin from carrying oxygen to the cells, resulting in hypemic hypoxia

• Aircraft heater vents and defrost vents may provide CO a passageway into the cabin, particularly if the engine exhaust system has a leak or is damaged

• Effects can include headache, blurred vision, dizziness, drowsiness, and/or loss of muscle power

• Immediate corrective action should be taken including turning off the heater, opening fresh air vents and windows, and using supplemental oxygen, if available

FAR 91.211

 Oxygen Requirements 

12,500' - 14,000'

Required for crew after 30 minutes

14,000' - 15,000'

Required for crew

Above 15,000'

Available for everyone

PHAK 17-19

• Light enters through the cornea at the front of the eyeball, travels through the lens, and falls on the retina

• The retina contains light sensitive cells that convert light energy into electrical impulses that travel through nerves to the brain

Cones

• Responsible for color vision, well suited to detecting fine detail and color in high light levels

• Fovea - the center of the visual field at the back of the retina where almost all the light sensing cells are cones and detail, color sensitivity, resolution are highest

Rods

• Unable to detect color, but detect movement and provide vision in dim light

• Farther from the fovea, the rods are more numerous and provide the major portion of night vision

Central Blind Spot

• The area where the optic nerve connects to the retina in the back of each eye is known as the optic disk

• There is a total absence of cones and rods in this area, and consequently, each eye is completely blind in this spot

• Under normal binocular vision conditions, this is not a problem because an object cannot be in the blind spot of both eyes at the same time

Photopic Vision

• Cones concentrated in the fovea centralis of the eye are primarily responsible for vision in bright light

• Provides the capability for seeing color and resolving fine detail during daylight or when a high level of artificial illumination exists

Mesopic Vision

• Achieved by a combination of rods and cones and is experienced at dawn, dusk, and during full moonlight

• Considered the most dangerous period for viewing, pilots should use off-center vision and proper scanning techniques

Scotopic Vision

• Experienced under low-light levels and the cones become ineffective, resulting in poor resolution

• Color perception is lost and a night blind spot in the central field of view appears at low light levels when the cone-cell sensitivity is lost

Night Vision

• To see an object clearly at night, the pilot must expose the rods to the image, this can be done by looking 5° to 10° off center of the object to be seen

AIM 8-1-2

PHAK 17-18

• Altitude-Induced Decompression Sickness (DCS) describes a condition characterized by a variety of symptoms resulting from exposure to low barometric pressures that cause inert gases (mainly nitrogen), normally dissolved in body fluids and tissues, to come out of physical solution and form bubbles

• If the nitrogen is forced to leave the solution too rapidly, bubbles form in different areas of the body causing a variety of signs and symptoms

• A pilot or passenger who intends to fly after scuba diving should allow the body sufficient time to rid itself of excess nitrogen absorbed during diving

• The recommended waiting time before going to flight altitudes of up to 8,000' is at least 12 hours after diving that does not require controlled ascent, and at least 24 hours after diving that does require controlled ascent

• The waiting time before going to flight altitudes above 8,000' should be at least 24 hours after any scuba dive