Introduction
As a pilot, it is important to stay aware of the psychological and physical standards required for the type of flying performed.
This chapter provides information on medical certification and on aeromedical factors related to flying activities.
Most pilots must have a valid medical certificate to exercise the privileges of their airman certificates. Balloon pilots
exercising student, sport or private pilot privileges, and commercial balloon pilots conducting flight instruction are not
required to hold a medical certificate. Balloon pilots exercising commercial pilot privileges for operations other than flight
instruction are required to hold at least a second-class medical certificate.
Some operations conducted outside the United States may require the balloon pilot to have a medical certificate when it is
otherwise not required in the United States. For example, United States certificated balloon pilots participating in events in
Canada may be required to hold a medical certificate in order to carry passengers. In this case, it would be wise to check
with the appropriate authorities to determine the requirements for specific operations. Title 14 of the Code of Federal
Regulations (14 CFR) part 67 covers medical certification of pilots. Aviation medical examiners (AMEs) may be found
using the FAA’s Find an Aviation Medical Examiner (AME) website.
Environmental & Health Factors Affecting Pilot Performance
A number of health factors and physiological effects can be linked to flying. Some are minor, while others are important
enough to require special consideration to ensure safety of flight. In some cases, physiological factors can lead to in-flight
emergencies. Some important medical factors that a pilot should be aware of include hypoxia, hyperventilation, middle ear
and sinus problems, motion sickness, stress and fatigue, dehydration, and heatstroke. Other subjects include the effects of
alcohol and drugs, anxiety, and excess nitrogen in the blood after scuba diving.
Hypoxia
Hypoxia means “reduced oxygen” or “not enough oxygen.” Although any tissue will die if deprived of oxygen long
enough, the main concern is usually with getting enough oxygen to the brain, since it is particularly vulnerable to oxygen
deprivation. Any reduction in mental function while flying can result in life-threatening errors. Hypoxia can be caused
by several factors, including an insufficient supply of oxygen, inadequate transportation of oxygen, or the inability of the
body tissues to use oxygen. Four forms of hypoxia based on their causes are: hypoxic hypoxia, hypemic hypoxia, stagnant
hypoxia, and histotoxic hypoxia.
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 in 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
Chapter 9: Aeromedical Factors
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 pilot flight risk during the recovery period.
Stagnant Hypoxia
Stagnant means “not flowing.” Stagnant hypoxia results when the oxygen-rich blood in the lungs is not moving, for one
reason or another, to the tissues that need it. One form of stagnant hypoxia is an arm or leg “going to sleep” because the
blood flow has accidentally been shut off. This kind of hypoxia can also result from shock, the heart failing to pump
blood effectively, or a constricted artery. Cold temperatures can also reduce circulation and decrease the blood supplied to
extremities.
Histotoxic Hypoxia
The inability of the cells to effectively use oxygen is defined as histotoxic hypoxia. “Histo” refers to tissues or cells, and
“toxic” means poison. In this case, plenty of oxygen is being transported to the cells that need it, but they are unable to
make use of it. This impairment of cellular respiration can be caused by alcohol and other drugs, such as narcotics and
poisons. Research has shown that drinking one ounce of alcohol can equate to an additional 2,000 feet of physiological
altitude. There are other issues concerning the use of alcohol in relation to flying in general; those will be discussed later
in this chapter.
Symptoms of Hypoxia
High altitude flying can place a pilot in danger of becoming hypoxic. Oxygen starvation causes the brain and other vital
organs to become impaired. One noteworthy attribute of the onset of hypoxia is that the first symptoms are euphoria and
a carefree feeling. With increased oxygen starvation, 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 reaction time.
• Impaired judgment.
• Euphoria.
• Visual impairment.
• Drowsiness.
• Lightheaded or dizzy sensation.
• Tingling in fingers and toes.
• Numbness.
As hypoxia worsens, the field of vision begins to narrow, and instrument interpretation can become difficult. Even with all
these symptoms, the effects of hypoxia can cause a pilot to have a false sense of security and be deceived into believing
that everything is normal. The treatment for hypoxia includes descending to lower altitudes and/or using supplemental
oxygen. Supplemental oxygen is required for certain operations above 12,500 feet mean sea level (MSL). (See 14 CFR
part 91, section 91.211.)
All pilots are susceptible to the effects of oxygen starvation, regardless of physical endurance or acclimatization. When
flying at high altitudes, it is paramount that oxygen be used to avoid the effects of hypoxia. The term “time of useful
consciousness” describes the maximum time the pilot has to make rational, life-saving decisions and carry them out at a
given altitude without supplemental oxygen. As altitude increases above 10,000 feet, the symptoms of hypoxia increase in
severity, and the time of useful consciousness rapidly decreases. Many pilots have established an altitude lower than the
required 12,500 MSL as their personal “do not exceed without oxygen” limit. All pilots are well advised to personalize
their performance at altitude.
Since symptoms of hypoxia can be different for each individual, the ability to recognize hypoxia can be greatly improved
by experiencing and witnessing the effects of it during an altitude chamber “flight.” The Federal Aviation Administration
provides this opportunity under professional supervision at the Civil Aeromedical Institute in Oklahoma City, or at selected
WINGS hypoxia demonstration events. To register and attend one of these courses, please visit the FAA’s Airman Education
Programs website.
Hyperventilation
Hyperventilation occurs when an individual is experiencing emotional stress, fright, or pain, and the breathing rate and
depth increase, although the carbon dioxide level in the blood is already at a reduced level. The result is an excessive loss
of carbon dioxide from the body, which can lead to unconsciousness due to the respiratory system’s overriding mechanism
to regain control of breathing
Pilots encountering an unexpected stressful situation may subconsciously increase their breathing rate. If flying at higher
altitudes, either with or without oxygen, a pilot may have a tendency to breathe more rapidly than normal, which often
leads to hyperventilation.
Since many of the symptoms of hyperventilation are similar to those of hypoxia, it is important to correctly diagnose and
treat the proper condition. If using supplemental oxygen, check the equipment and flow rate to ensure the symptoms are
not hypoxia related.
Common symptoms of hyperventilation include:
• 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.
Hyperventilation may produce a pale, clammy appearance and muscle spasms compared to the cyanosis and limp muscles
associated with hypoxia. The treatment for hyperventilation involves restoring the proper carbon dioxide level in the body.
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. Recovery is usually rapid once the
breathing rate is returned to normal.
Middle Ear & Sinus Problems
Ascents and descents can sometimes cause ear or sinus pain and a temporary reduction in the ability to hear. The
physiological explanation for this discomfort is a difference between the pressure of the air outside the body and that of the
air inside the middle ear and nasal sinuses.
The middle ear is a small cavity located in the bone of the skull. It is closed off from the external ear canal by the eardrum.
Normally, pressure differences between the middle ear and the outside world are equalized by a tube leading from inside
each ear to the back of the throat on each side, called the eustachian tube. These tubes are usually closed, but open during
chewing, yawning, or swallowing to equalize pressure. Even a slight difference between external pressure and middle ear
pressure can cause discomfort.
In a similar way, air pressure in the sinuses equalizes with the ambient or outside pressure through small openings that
connect the sinuses to the nasal passages. An upper respiratory infection, such as a cold or sinusitis, or a nasal allergic
condition can produce enough congestion around an opening to slow equalization. As the difference in pressure between the
sinus and the ambient atmosphere increases, congestion may plug the opening. This “sinus block” occurs most frequently
during descent. Slow descent rates can reduce the associated pain. A sinus block can occur in the frontal sinuses, located
above each eyebrow, or in the maxillary sinuses, located in each upper cheek. It will usually produce excruciating pain
over the sinus area. A maxillary sinus block can also make the upper teeth ache. Bloody mucus may discharge from the
nasal passages.
Sinus block [ Figure 9-1] can be avoided by not flying with an upper respiratory infection or nasal allergic condition.
Adequate protection is usually not provided by decongestant sprays or drops to reduce congestion around the sinus
openings. Oral decongestants have side effects that can impair pilot performance. If a sinus block does not clear shortly
after landing, a physician should be consulted.
Opening to Throat
Middle Ear
Outer Ear
Auditory Canal
Eustachian Tube
Eardrum
Figure 9-1. The eustachian tube allows air pressure to equalize in the middle ear.
During a climb, middle ear air pressure may exceed the pressure of the air in the external ear canal, causing the eardrum to
bulge outward. Pilots become aware of this pressure change when they experience alternate sensations of “fullness” and
“clearing.” During descent, the reverse happens. While the pressure of the air in the external ear canal increases, the middle
ear cavity, which equalized with the lower pressure at altitude, is at lower pressure than the external ear canal. This results
in the higher outside pressure, causing the eardrum to bulge inward.
This condition can be more difficult to relieve due to the fact that the partial vacuum tends to constrict the walls of the
Eustachian tube. To remedy this often painful condition, which also causes a temporary reduction in hearing sensitivity,
pinch the nostrils shut, close the mouth and lips, and blow slowly and gently into the mouth and nose. This is commonly
referred to as the Valsalva procedure.
The Valsalva procedure forces air through the eustachian tube into the middle ear. It may not be possible to equalize the
pressure in the ears if a pilot has a cold, an ear infection, or sore throat. A flight in this condition can be extremely painful,
as well as damaging to the eardrums. If a pilot experiences minor congestion, nose drops or nasal sprays may reduce the
risk of a painful ear blockage.
Spatial Disorientation & Illusions
Balloon pilots rarely experience issues with spatial disorientation while in flight, as virtually all balloon operations are
conducted under visual flight rules (VFR) conditions. Knowledge of these conditions, however, is important in the event
of unusual circumstances or situations, such as inadvertently being caught in fog, or perhaps in areas of low visibility. The
balloon pilot should have an awareness of these issues, so that appropriate actions may be taken as necessary.
Spatial disorientation specifically refers to the lack of orientation with regard to the position, attitude, or movement of an
aircraft in space. The body uses three integrated systems working together to ascertain orientation and movement in space.
The eye is by far the largest source of information. Kinesthesia refers to the sensation of position, movement, and tension
perceived through the nerves, muscles, and tendons. The vestibular system is a very sensitive motion-sensing system
located in the inner ears. It reports head position, orientation, and movement in three-dimensional space.
All this information comes together in the brain and, most of the time, the three streams of information agree, giving a clear
idea of where and how the body is moving. Flying can sometimes cause these systems to supply conflicting information
to the brain, which can lead to disorientation. During flight in visual meteorological conditions (VMC), the eyes are the
major orientation source and usually prevail over false sensations from other sensory systems. When these visual cues are
removed, as they are in instrument meteorological conditions (IMC), false sensations can cause a pilot to quickly become
disoriented.
The vestibular system in the inner ear allows the pilot to sense movement and determine orientation in the surrounding
environment. In both left and right inner ears, three semicircular canals are positioned at approximate right angles to
each other. [Figure 9-2] Each canal is filled with fluid and has a section full of fine hairs. Acceleration of the inner ear in
any direction causes the tiny hairs to deflect, which in turn stimulate nerve impulses, sending messages to the brain. The
vestibular nerve transmits the impulses from the utricle, saccule, and semicircular canals to the brain to interpret motion.
YAW
ROLL
YAW
PITCH
PITCH ROLL
The semicircular tubes are arranged
at right angles to each other in the roll,
pitch, and yaw axes.
Vestibular Nerve
Endolymph Fluid
Ampulla of Semicircular Canal
Hair Cells
Cupola
Semicircular Canal
Otolith Organ
Figure 9-2. The semicircular canals lie in three planes, and sense motions of roll, pitch, and yaw.
The postural system sends signals from the skin, joints, and muscles to the brain that are interpreted in relation to the
Earth’s gravitational pull. These signals determine posture. Inputs from each movement update the body’s position to the
brain on a constant basis. “Seat of the pants” flying is largely dependent upon these signals. Used in conjunction with visual
and vestibular clues, these sensations can be fairly reliable. However, the body cannot distinguish between acceleration
forces due to gravity and those resulting from maneuvering the aircraft, which can lead to sensory illusions and false
impressions of an aircraft’s orientation and movement.
Again, under normal flight conditions, most balloon pilots and passengers do not experience spatial disorientation (or
vertigo) while flying.
Motion Sickness
Under normal flight conditions, motion sickness is not an issue for most pilots or passengers. Motion sickness, or
airsickness, is caused by the brain receiving conflicting messages about the state of the body. A pilot or passengers may
experience motion sickness during initial flights, but it generally goes away within the first few flights. Anxiety and stress,
which may be experienced at the beginning of flight training, can also contribute to motion sickness. Symptoms of motion
sickness include general discomfort, nausea, dizziness, paleness, sweating, and vomiting.
Stress
Stress is defined as the body’s response to physical and psychological demands placed upon it. 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. Blood sugar, heart rate, respiration, blood pressure, and perspiration all increase. The term “stressor”
is used to describe an element that causes an individual to experience stress. Examples of stressors include physical stress
(noise or vibration), physiological stress (fatigue), and psychological stress (difficult work or personal situations).
Stress falls into two broad categories: acute (short term) and chronic (long term). Acute stress involves an immediate threat
that is perceived as danger. This is the type of stress that 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 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 financial worries,
difficult relationships, 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. Pilots experiencing this level of stress are
not safe and should not exercise their airman privileges. Pilots who suspect they are suffering from chronic stress should
consult a physician.
Fatigue
Fatigue is frequently associated with pilot error. Some of the effects of fatigue include degradation of attention and
concentration, impaired coordination, and decreased ability to communicate. These factors can seriously influence the
ability to make effective decisions. Physical fatigue can result from sleep loss, exercise, or physical work. Factors such as
stress and prolonged performance of cognitive work can result in mental fatigue.
Like stress, fatigue also falls into two broad categories: acute and chronic. Acute fatigue is 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. Rest after exertion and 8 hours of sound sleep ordinarily cures this condition.
A special type of acute fatigue is skill fatigue. This fatigue can be readily seen in the balloon pilot who, for example, has
driven most or all of the night in order to attend an event, or perhaps was up for most of the previous night. [Figure 9-3]
Figure 9-3. This pilot drove all night to make an event, but still will not be able to fly.
This type of fatigue has two main effects on performance:
• 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 as a 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 may be accompanied by loss of accuracy and smoothness in control
movements.
Acute fatigue has many causes, but the following are among the most important to the pilot:
• Mild hypoxia (oxygen deficiency).
• Physical stress.
• Psychological stress.
• Depletion of physical energy resulting from psychological stress.
Sustained psychological stress accelerates the glandular secretions that prepare the body for quick reactions during an
emergency. These secretions make the circulatory and respiratory systems work harder, and the liver releases energy to
provide the extra fuel needed for brain and muscle work. When this reserve energy supply is depleted, the body lapses into
generalized and severe fatigue.
Acute fatigue can be prevented by proper diet and adequate rest and sleep. A well-balanced diet prevents the body from
consuming its own tissues as an energy source. Adequate rest maintains the body’s store of vital energy.
Chronic fatigue, extending over a long period of time, usually has psychological roots, although an underlying disease
is sometimes responsible. Continuous high stress levels, for example, can produce chronic fatigue. Chronic fatigue is