Introduction
The study of human factors involves different disciplines. [ Figure 13-1] When referring to human factors, engineers
sometimes refer to the 3Ds: design, development, and deployment of systems that improve the system/human interface.
Study of human factors also involves understanding and preventing human errors engineers cannot prevent using the 3Ds.
This chapter focuses on the human element—pilot attitudes, pilot error, physiological issues related to soaring safety, pilot
management of a glider and its systems, and pilot decision-making as a process that can mitigate glider flight risk and
prevent many common types of accidents. For more information on human factors and risk, see the Risk Management
Handbook (FAA-H-8083-2) or the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25).
Cognitive Science
Industrial Organizational Psychology
Not Complex Flight
Exercise Caution
Area of Concern
Endangerment
Low Risk
Educational Psychology
Safety Engineering
Medical Science
Computer Science
Anthropometric Science
Experimental Psychology
Clinical Psychology
Industrial Engineering
Human
Factors
Figure 13-1. Human factor disciplines.
Recognizing Hazardous Attitudes
Hazardous attitudes lead to hazardous behaviors that include complacency, indiscipline, and overconfidence, which all
increase the risk of a glider accident.
Complacency
Complacency can occur if a pilot feels a false sense of security about the surroundings. This could affect a glider pilot who
just wants to fly and does not comprehend the hazards and associated risks. Complacency also affects glider pilots who no
longer feel obligated to adhere to standard safety precautions (e.g., “I’ve done this a million times and don’t need to refer
to a checklist.”).
A few countermeasures include:
• Setting aside sufficient time to prepare for each flight.
• Examining hazards and addressing the associated risk of each flight.
• Challenging oneself to meet a standard of excellence on each flight.
Chapter 13: Human Factors
Indiscipline
Aviation accidents sometimes result from pilot failure to comply with regulatory standards. Having the discipline to follow
the rules reduces the chance of an accident.
The regulatory requirements set a standard for safety. Pilots should consider developing more stringent personal limitations
that may be modified as their experience and proficiency grow. For example, the pilot could establish minimum visibility
and wind conditions for flight. In that case, the pilot would not fly if conditions exceeded established personal minimums.
A disciplined pilot would only lower personal minimums based on training and rational decision making and not based on
a desire to make a particular flight. In addition, a pilot might raise the minimums if under additional stress from personal
or work-related issues or if flying infrequently.
Sometimes pilots feel their experience has taught them an easier or faster way to do certain tasks. They should ask
themselves if their attitude and procedures align with guidelines set forth by disciplined aviators. If not, these pilots should
consider that standardized procedures, rules, and formal risk mitigation strategies offer better protection from accidents.
Pilots interested in more information about a disciplined approach to aviation safety can refer to the FAA Risk Management
Handbook (FAA-H-8083-2), which describes structured techniques pilots can use that include how to set or revise personal
minimums and how to conduct a disciplined and thorough safety analysis before flight.
Overconfidence
A realistic level of confidence enables a pilot to feel good about a particular flight operation. That confidence comes from
experience, training, proficiency, adequate preparation for a flight, and ongoing discipline.
Overconfidence reflects a lack of understanding about the pilot’s own limitations, not understanding the aircraft or
conditions that could threaten the safety of flight, denial of the reality of pilot shortcomings, or a desire to prove something.
Whatever the cause, unjustified confidence can lead to an accident. Pilots should carefully consider their limitations when
attempting to fly in an unfamiliar glider or in an unfamiliar environment and resist letting overconfidence or pride interfere
with good judgment. Glider pilots who do not fly regularly or who have not flown for several months should recognize
the different levels of safety that come from having a current flight review every two years, meeting take-off and landing
currency requirements, and having the level of proficiency necessary given the current conditions.
Pilot Error
All pilots make errors, and many pilots may have gaps in knowledge. Training assessments, flight examinations (written
or oral), operational checks, critiques, and post-flight pilot self-assessments can highlight what a pilot can do better. An
honest and fair assessment can lead to correction of any shortcomings and reduce the potential for accidents.
Types of Errors
One type of unintentional error involves failure to perform an intended action within acceptable tolerances. On the other
hand, an incorrect opinion, bad judgment, poor reasoning, careless attitude, or insufficient knowledge can cause a more
serious mistake. For example, a pilot with good stick and rudder skills but new to ridge soaring might fly into strong sink
on the downwind side of a ridge and narrowly escape hitting terrain. The pilot’s lack of knowledge and bad judgment could
lead to this kind of mistake.
Intentional
If a pilot knowingly does something wrong, that pilot intentionally deviated from safe practices, procedures, standards, or
regulations. In aviation, an intentional error suggests a serious and underlying lack of concern for safety. The pilot should
reflect on the reason for the error, seek advice or counseling, and not fly unless able to prevent that behavior.
Physiological/Medical Factors that Affect Pilot Performance
Fatigue
Fatigue involves a reduction or impairment in any of the following: cognitive ability, decision-making, reaction time,
coordination, speed, strength, and balance. Fatigue reduces alertness and often reduces a person’s ability to focus and hold
attention on a task. [Figure 13-2] Emotional fatigue exists and can affect mental and physical performance. Lack of sleep,
stress, and overwork can all cause or aggravate fatigue.
Unrefreshing
sleep
Headaches
Fatigue
Pain
Poor concentration
Irritable mood
Loss of
motivation
Loss of
pleasure
Panic attacks
Avoidant
behaviour
Diarrhea/
constipation
Abdominal pain
Bloating
Myalgia
arthralgia
Tender
points
Chronic fatigue syndrome
FibromyalgiaDepression
Anxiety
Irritable bowel syndrom
Prolonged
fatigue states
Figure 13-2. Sampling of factors that interact with fatigue.
A person’s mental and physical state naturally cycles through various levels of performance each day. Variables such as
body temperature, blood pressure, heart rate, blood chemistry, alertness, and attention rise and fall in a daily pattern known
as a circadian rhythm. [Figure 13-3] A person’s ability to work and rest rises and falls during this cycle. Activity contrary to
a person’s circadian rhythm can cause subtle difficulties and fatigue. An affected person might not recognize this situation.
Since another person might alert a pilot to the signs of fatigue, flying a glider alone when fatigued creates a particularly
dangerous situation. For example, a fatigued glider pilot might not actively see and avoid other traffic. Pilots should avoid
flying when not having full night’s rest, after working excessive hours, or after an especially exhausting or stressful day.
Figure 13-3. Many human performance factors rise and fall daily.
The best remedy for fatigue involves getting enough sleep on a regular basis. Pilots should track their hours and quality
of sleep for fatigue awareness. Countermeasures to fatigue such as caffeine, may work for a short duration, but many
countermeasures may make fatigue worse over the long term. Pilots should exercise caution if using medication to fight
fatigue since a fatigued person may have trouble getting needed rest after using medication. A pilot experiencing ongoing
fatigue issues or chronic fatigue, should stop flying a glider, consult a physician, and resolve the issue before flying again.
Hyperventilation
Hyperventilation results when a person breathes at an increased rate or breathes more deeply, which reduces the level of
carbon dioxide in the blood. Reduced carbon dioxide in the blood can raise blood pH and lead to undesirable health effects.
Hyperventilation might occur as result of emotional stress, fright, or pain. Glider pilots who encounter extreme or
unexpected turbulence or strong areas of sink over rough terrain or water may unconsciously increase their breathing rate
or breathing volume. When flying at higher altitudes, either with or without oxygen, a tendency to breathe more rapidly
than normal may occur.
Figure 13-4 lists the common symptoms of hyperventilation. Treatment for hyperventilation involves restoring the proper
carbon dioxide level. Consciously slowing the breathing rate or talking aloud can reverse the effects of hyperventilation.
Recovery usually occurs rapidly once the breathing rate returns to normal. In rare cases, hyperventilation can cause
unconsciousness.
Headache
Decreased reaction time
Impaired judgment
Euphoria
Visual impairment
Drowsiness
Lightheaded or dizzy sensation
Tingling in fingers and toes
Numbness
Pale, clammy appearance
Muscle spasms
Common Symptoms of Hyperventilation
Figure 13-4. Common symptoms of hyperventilation.
Hypoxia
Hypoxia results from reduced oxygen or not enough oxygen. Although human cell tissue will die if deprived of oxygen
long enough, the principal concern for pilots is lack of oxygen to the brain, which can reduce cognitive ability and result
in life-threatening errors. Hypoxia has several causal factors, including an insufficient supply of oxygen, inadequate
transportation of oxygen, or the inability of the body tissues to use oxygen. The forms of hypoxia are based on their causes:
Hypoxic Hypoxia
Hypoxic hypoxia results from insufficient oxygen available to the body as a whole. The reduction in partial pressure of
oxygen at high altitude can cause a pilot to experience this type of hypoxia. As an unpressurized aircraft ascends during
flight, the percentage of atmospheric oxygen remains constant, but a reduced number of oxygen molecules enter the lungs
and pass between the membranes within the respiratory system.
Hypemic Hypoxia
Hypemic hypoxia occurs when the blood cannot take up sufficient oxygen. Causes of this form of hypoxia include reduced
blood volume from severe bleeding or certain blood diseases, such as anemia. Carbon monoxide poisoning causes this type
of hypoxia. Hemoglobin, the blood molecule that transports oxygen, becomes chemically unable to bind oxygen molecules
if exposed to carbon monoxide. Hypemic hypoxia can also occur after a blood donation. While blood volume normalizes
quickly following a donation, restoring the lost hemoglobin can take several weeks. Although the effects of the blood loss
seem slight at ground level, blood donation can create a flight risk during the recovery period.
Stagnant Hypoxia
Stagnant hypoxia or ischemia results when the oxygen-rich blood in the lungs does not move to the tissues that need it. An
arm or leg going to sleep because of restricted blood flow is one form of stagnant hypoxia. This kind of hypoxia can also
result from shock, the heart failing to pump blood effectively, or a constricted artery. During flight, excessive G forces can
cause stagnant hypoxia. Cold temperatures can also reduce circulation and decrease blood supply to extremities.
Histotoxic Hypoxia
When histotoxic hypoxia occurs, the body transports enough oxygen to the cells, but they cannot make use of it. This
impairment of respiration at the cellular level may result from alcohol consumption, exposure to certain drugs or narcotics,
or exposure to poisons.
Symptoms of Hypoxia
Oxygen starvation causes impairment of the brain and other vital organs. The first symptoms of hypoxia can include
euphoria and a carefree feeling. With increased oxygen deprivation, the extremities become less responsive and flying
becomes less coordinated. The symptoms of hypoxia vary with the individual, but common symptoms include:
• Cyanosis (blue fingernails and lips).
• Headache
• Decreased response to stimuli and increased reaction time,
• Impaired judgment
• Euphoria
• Visual impairment
• Drowsiness
• Lightheaded or dizzy sensation
• Tingling in fingers and toes
• Numbness
As hypoxia worsens, the pilot's field of vision begins to narrow, and instrument interpretation can become difficult. Even
with all these symptoms, the effects of hypoxia can give a pilot a false sense of security.
Treatment of Hypoxia
Treatment for hypoxia involves increasing the amount of available oxygen. Pilots commonly descend to lower altitudes
or use supplemental oxygen to counteract the effects of hypoxia. Time of useful consciousness gives the maximum time
available for the pilot to make rational, life-saving decisions and carry them out at a specific altitude without supplemental
oxygen. As altitude increases above 10,000 feet, the symptoms of hypoxia increase, and the time of useful consciousness
diminishes significantly. [Figure 13-5]
Altitude Time of useful consciousness
45,000 feet MSL
40,000 feet MSL
35,000 feet MSL
30,000 feet MSL
28,000 feet MSL
25,000 feet MSL
22,000 feet MSL
20,000 feet MSL
9 to 15 seconds
15 to 20 seconds
30 to 60 seconds
1 to 2 minutes
2½ to 3 minutes
3 to 5 minutes
5 to 10 minutes
30 minutes or more
Figure 13-5. Time of useful consciousness.
Since individuals experience hypoxia differently, experiencing the effects of hypoxia in an altitude chamber [Figure 13-6]
can improve an individual’s recognition of their own symptoms. The Federal Aviation Administration (FAA) provides this
opportunity through aviation physiology training, which occurs at the FAA Civil Aerospace Medical Institute (CAMI) in
Oklahoma City, Oklahoma, and at many military facilities across the United States. For information about the FAA’s one-
day physiological training course with altitude chamber and vertigo demonstrations, visit the FAA website.
Figure 13-6. CAMI altitude chamber.
Inner Ear Discomfort
The internal pressure of the middle ear cavity changes more slowly than the pressure outside the ear. A pressure difference
can develop during an ascent or descent, which may result in temporary hearing loss, discomfort, pain, and distraction
from flight tasks.
When a glider ascends, middle ear air pressure may exceed the pressure of the air in the external ear canal, causing the
eardrum to bulge outward. This condition usually resolves itself, and the pilot may notice a popping sound as pressure
equalizes and hearing sensitivity returns to normal. During a descent, pressure of the air in the external ear canal may
increase above that of the middle ear cavity, which causes the eardrum to bulge inward. The condition during a descent
seems more painful and unpleasant to most people. Nasal congestion or a cold can make pressure equalization difficult
or impossible. Chewing gum, sucking on hard candy, or swallowing might assist pressure equalization during a descent.
Discomfort during a descent ends when enough air flows into the middle ear through the eustachian tube. However, the
lower pressure in the middle ear tends to constrict the walls of the eustachian tube and prevent the flow of air to the middle
ear. A pilot can try the Valsalva maneuver to correct this situation. The pilot should pinch the nostrils, close the mouth and
lips, and blow slowly and gently in the mouth and nose to force air up the eustachian tube into the middle ear.
Scuba Diving
Scuba diving subjects the body to increased pressure, which dissolves more nitrogen in body tissues and fluids. The
reduction of atmospheric pressure that accompanies flying can produce physical problems for scuba divers when small
bubbles of nitrogen to form inside the body as the gas comes out of solution. These bubbles can cause a painful and
potentially incapacitating condition called the bends.
Scuba training emphasizes how to prevent the bends when rising to the surface of a body of water. However, excess
nitrogen can remain in tissue fluids for several hours after finishing a dive. A pilot who SCUBA dives can experience
the bends from as low as 8,000 feet MSL, with increasing severity as altitude increases. As noted in the Aeronautical
Information Manual (AIM), the minimum recommended time between scuba diving on non- decompression stop dives
and flying is 12 hours, while the minimum time recommended between decompression stop diving and flying is 24 hours.
Spatial Disorientation
Most gliders used for primary training have basic instrumentation only, and glider pilots do not normally train for flight
solely by reference to instruments. Glider pilots should avoid flight in low visibility or in any condition that makes
discerning the horizon difficult. These conditions increase the likelihood that the pilot will succumb to an illusion and
experience a loss of control. [ Figure 13-7] Glider pilots who fly in marginal visibility should establish and abide by
personal minimums for visibility.
Figure 13-7. Flying in haze or other restrictions to visibility increases the likelihood of spatial disorientation.
Flight in a powered glider may occur at night or in instrument conditions provided the glider meets the requirements of 14
CFR part 91, section 91.205, and the pilot meets the applicable requirements of 14 CFR part 61, section 61.57. Pilots have
fewer visual cues available to judge flight attitude at night or in instrument conditions. Both regimes present additional
potential for illusions, navigation errors, collisions, and loss of control. In addition, any emergency at night becomes much
more difficult to handle. Glider pilots who fly in these conditions normally have ratings in other aircraft categories that
include training and testing for night or instrument conditions. A glider pilot without additional training, certification,
recency, and proficiency should avoid night or instrument operations.
Dehydration
Glider pilots often fly for long periods of time in hot summer temperatures or at high altitudes that can cause dehydration.
Although the effects of dehydration may develop slowly, fluid loss from perspiration and breathing can result in fatigue and
progress to dizziness, weakness, nausea, tingling of hands and feet, abdominal cramps, and extreme thirst. [Figure 13-8]
Physical activity
Loss of fluid
Breathing
Sweating
Reduced circulation
Reduced nutrients
Blood more viscous
Blood circulation slows
Leads to:
• Nausea
• Headaches,
• Irrationality
• Muscle cramps
• Rise in body
• Temperature
• Dizziness
Dehydration
Figure 13-8. Symptoms of dehydration.
Pilots should take water on every flight to prevent dehydration. Some glider pilots wear a hat with a rim for shade and to
keep a cool head. Pilots should ensure that the brim of the hat does not interfere with the ability to scan for other gliders
and air traffic.
Heatstroke
Heatstroke results when the body cannot control excessive high temperature. Onset of this condition may mimic
dehydration, but it may also lead to collapse. To prevent these symptoms, the pilot should carry an ample supply of water
and use it at frequent intervals on any long flight, even if not thirsty. Wearing light-colored, porous clothing and a hat
provides protection from the sun. Ventilating the cabin also helps remove excess heat.
Cold Weather
Preparing for extreme cold may seem odd when comfortable temperatures exist at ground level on wave soaring days.
However, when flying at high altitudes, the inside of the glider can get cold. A glider at a high altitude can encounter
temperatures of -30° to -60 °C. When soaring, sunshine through the canopy can keep the pilot’s upper body warm for a
time, but shaded legs and feet can quickly chill or suffer frostbite. After an hour or two at such temperatures, even the
upper body can become quite cold. Layered, loose-fitting clothing helps insulate body heat. Either wool gloves or fitted
gloves with mittens over them can protect the hands. Two or three pairs of socks in layers with silk on the inside and wool
on the outside plus an insulated boot can help keep feet comfortable. Clothing manufacturers produce clothing and socks