Introduction
It is important for a pilot to be aware of the mental and
physical standards required for the type of flying performed.
This chapter provides information on medical certification and
on a variety of aeromedical factors related to flight activities.
Aeromedical
Factors
Chapter 17
Obtaining a Medical Certificate
Most pilots must have a valid medical certificate to exercise
the privileges of their airman certificates. Glider and free
balloon pilots are not required to hold a medical certificate.
Sport pilots may hold either a medical certificate or a valid
state driver’s license. Regardless of whether a medical
certificate or drivers license is required, 14 CFR 61.53
requires every pilot not to act as a crewmember if they know,
or have reason to know, of any medical condition that would
make them unable to operate the aircraft in a safe manner.
Acquisition of a medical certificate requires an examination
by an aviation medical examiner (AME), a physician
with training in aviation medicine designated by the Civil
Aerospace Medical Institute (CAMI). There are three classes
of medical certificates. The class of certificate needed
depends on the type of flying the pilot plans to perform.
A third-class medical certificate is required for a private or
recreational pilot certificate. It is valid for 5 years for those
individuals who have not reached the age of 40; otherwise it
is valid for 2 years. A commercial pilot certificate requires at
least a second-class medical certificate, which is valid for 1
year. First-class medical certificates are required for airline
transport pilots and are valid for one year if the airman is 40
or younger; 40 and older it is valid for 6 months.
The standards are more rigorous for the higher classes of
certificates. A pilot with a higher class medical certificate
has met the requirements for the lower classes as well. Since
the required medical class applies only when exercising the
privileges of the pilot certificate for which it is required, a
first-class medical certificate would be valid for 1 year if
exercising the privileges of a commercial certificate and 2 or 5
years, as appropriate, for exercising the privileges of a private
or recreational certificate. The same applies for a second-class
medical certificate. The standards for medical certification
are contained in Title 14 of the Code of Federal Regulations
(14 CFR) part 67 and the requirements for obtaining medical
certificates can be found in 14 CFR part 61.
Students who have physical limitations, such as impaired
vision, loss of a limb, or hearing impairment may be issued
a medical certificate valid for “student pilot privileges only”
while learning to fly. Pilots with disabilities may require
special equipment to be installed in the aircraft, such as
hand controls for pilots with paraplegia. Some disabilities
necessitate a limitation on the individual’s certificate; for
example, impaired hearing would require the limitation
“not valid for flight requiring the use of radio.” When all the
knowledge, experience, and proficiency requirements have
been met and a student can demonstrate the ability to operate
the aircraft with the normal level of safety, a “statement of
demonstrated ability” (SODA) can be issued. This waiver,
or SODA, is valid as long as the physical impairment does
not worsen. Contact the local Flight Standards District Office
(FSDO) for more information on this subject.
The FAA medical standards, 14 CFR part 67, specify fifteen
medical conditions that are considered disqualifying by
“history or clinical diagnosis.” Regardless of when one of
these conditions was diagnosed and treated, an airman may
not be issued a medical certificate except through a process
called a “Special Issuance Authorization,” as explained
in 14 CFR part 67, section 67.401. A special issuance is a
discretionary issuance by the FAA Federal Air Surgeon and
requires satisfactory completion of special testing determined
by the FAA to demonstrate that an airman is safe to fly for
the duration of the medical certificate issued. The specific
disqualifying conditions include:
• Diabetes mellitus requiring oral hypoglycemic
medication or insulin
• Angina pectoris
• Coronary heart disease that has been treated or, if
untreated, that has been symptomatic or clinically
significant
• Myocardial infarction
• Cardiac valve replacement
• Permanent cardiac pacemaker
• Heart replacement
• Psychosis
• Bipolar disorder
• Personality disorder that is severe enough to have
repeatedly manifested itself by overt acts
• Substance dependence (including alcohol)
• Substance abuse
• Epilepsy
• Disturbance of consciousness and without satisfactory
explanation of cause
• Transient loss of control of nervous system function(s)
without satisfactory explanation of cause
However, this list includes only the mandatory disqualifying
conditions. There are many other medical conditions that fall
into the General Medical Condition section of the regulations
that are considered by the FAA to be disqualifying even
though they are not stated in the regulations. Conditions
such as cancer, kidney stones, neurologic and neuromuscular
conditions including Parkinson’s disease and multiple
sclerosis, certain blood disorders, and other conditions that
may progress over time require review by the FAA before a
medical certificate may be issued.
The important thing to remember is that with very few
exceptions, all disqualifying medical conditions may
be considered for special issuance. If you can present
satisfactory medical documentation to the FAA that your
condition is stable, the chances are good that you will be
able to qualify for an Authorization.
Health and Physiological 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 attention to ensure safety of flight.
In some cases, physiological factors can lead to inflight
emergencies. Some important medical factors that a pilot
should be aware of include hypoxia, hyperventilation,
middle ear and sinus problems, spatial disorientation, motion
sickness, carbon monoxide (CO) poisoning, 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 greatest concern regarding hypoxia during
flight is lack of 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.
The forms of hypoxia are based on their causes:
• Hypoxic hypoxia
• Hypemic hypoxia
• Stagnant hypoxia
• Histotoxic hypoxia
Hypoxic Hypoxia
Hypoxic hypoxia is a result of insufficient oxygen available
to the body as a whole. A blocked airway and drowning
are obvious examples of how the lungs can be deprived of
oxygen, but the reduction in partial pressure of oxygen at high
altitude is an appropriate example for pilots. Although the
percentage of oxygen in the atmosphere is constant, its partial
pressure decreases proportionately as atmospheric pressure
decreases. As an aircraft ascends during flight, the percentage
of each gas in the atmosphere remains the same, but there are
fewer molecules available at the pressure required for them
to pass between the membranes in the respiratory system.
This decrease in number of oxygen molecules at sufficient
pressure can lead to hypoxic hypoxia.
Dangers of Transporting Dry Ice
Sublimation is a process in which a substance transitions
from a solid to a gaseous state without passing through
an intermediate liquid state. Dry ice sublimates into large
quantities of CO2 gas, which can rapidly displace oxygen-
containing air and potentially cause hypoxia via carbon
dioxide intoxication. Case studies have shown that both illness
and death can be caused by occupational and/or unintentional
exposure when transporting dry ice in small, confined
spaces such as a flightdeck or airplane. Exposure to high
concentration of CO2 gas may lead to increased respiration,
tachycardia, cardiac arrhythmia, and unconsciousness.
Exposure to concentration of CO2 gas in excess of 10 percent
may cause convulsions, coma, and/or death.
The tendency of dry ice to rapidly sublimate also means that
without proper ventilation, it can rapidly pressurize. For
this reason, dry ice should never be placed inside a sealed
transport container (i.e., leak-proof secondary container)
and must be placed within an outer shipping container or
storage container that allows adequate ventilation to release
the CO2 gas and avoid pressurization. Sealing dry ice within a
leak-proof container may result in explosion of the container
potentially leading to serious physical injury or death.
Hypemic Hypoxia
Hypemic hypoxia occurs when the blood is not able to take
up and transport a sufficient amount of oxygen to the cells
in the body. Hypemic means “not enough blood.” This type
of hypoxia is a result of oxygen deficiency in the blood,
rather than a lack of inhaled oxygen, and can be caused by
a variety of factors. It may be due to reduced blood volume
(from severe bleeding), or it may result from certain blood
diseases, such as anemia. More often, hypemic hypoxia
occurs because hemoglobin, the actual blood molecule that
transports oxygen, is chemically unable to bind oxygen
molecules. The most common form of hypemic hypoxia is
CO poisoning. This is explained in greater detail later in this
chapter. Hypemic hypoxia can also be caused by the loss
of blood due to blood donation. Blood volume can require
several weeks to return to normal following a donation.
Although the effects of the blood loss are slight at ground
level, there are risks when flying during this time.
Stagnant Hypoxia
Stagnant means “not flowing,” and stagnant hypoxia or
ischemia results when the oxygen-rich blood in the lungs
is not moving, for one reason or another, to the tissues that
Figure 17-1. Time of useful consciousness.
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
need it. An arm or leg “going to sleep” because the blood
flow has accidentally been shut off 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, stagnant hypoxia can occur with
excessive acceleration of gravity (Gs). 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 poisonous. In this case, enough 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.
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. The first symptoms of hypoxia
can include 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 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 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
everything is normal.
Treatment of Hypoxia
Treatment for hypoxia includes flying at lower altitudes and/
or using supplemental oxygen. 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. [Figure 17-1]
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 (FAA) provides this opportunity through
aviation physiology training, which is conducted at the FAA
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
at www.faa.gov.
Hyperventilation
Hyperventilation is the excessive rate and depth of respiration
leading to abnormal loss of carbon dioxide from the blood.
This condition occurs more often among pilots than is
generally recognized. It seldom incapacitates completely, but
it causes disturbing symptoms that can alarm the uninformed
pilot. In such cases, increased breathing rate and anxiety
further aggravate the problem. Hyperventilation 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
Figure 17-2. The Eustachian tube allows air pressure to equalize
in the middle ear.
Opening to throat
Middle ear
Outer ear
Auditory canal
Eustachian tube
Eardrum
not hypoxia related. Common symptoms of hyperventilation
include:
• Visual impairment
• Unconsciousness
• Lightheaded or dizzy sensation
• Tingling sensations
• Hot and cold sensations
• Muscle spasms
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 and Sinus Problems
During climbs and descents, the free gas formerly present in
various body cavities expands due to a difference between
the pressure of the air outside the body and that of the air
inside the body. If the escape of the expanded gas is impeded,
pressure builds up within the cavity and pain is experienced.
Trapped gas expansion accounts for ear pain and sinus pain,
as well as a temporary reduction in the ability to hear.
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. [Figure 17-2]
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 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 experiencing minor congestion,
nose drops or nasal sprays may reduce the risk of a painful
ear blockage. Before using any medication, check with an
AME to ensure that it will not affect the ability to fly.
In a similar way, air pressure in the sinuses equalizes with
the pressure in the flight deck 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 sinuses and the flight deck 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 usually produces 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 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.
Figure 17-3. The semicircular canals lie in three planes and sense motions of roll, pitch, and yaw.
YAW
ROLL
YAW
PITCH
PITCH ROLL
The semicircular tubes are arranged
at approximately, right angles to each
other in the roll, pitch, and yaw axes. Vestibular nerve
Endolymph fluid
Ampulla of semicircular canal
Hair cells
Cupola
Semicircular canals
Otolith organ
Spatial Disorientation and Illusions
Spatial disorientation specifically refers to the lack of
orientation with regard to the position, attitude, or movement
of the airplane in space. The body uses three integrated
systems that work together to ascertain orientation and
movement in space.
• Vestibular system—organs found in the inner ear that
sense position by the way we are balanced
• Somatosensory system—nerves in the skin, muscles,
and joints that, along with hearing, sense position
based on gravity, feeling, and sound
• Visual system—eyes, which sense position based on
what is seen
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 the left and right inner ear, three
semicircular canals are positioned at approximate right angles
to each other. [Figure 17-3] 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 stimulates 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.
The somatosensory 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.
Under normal flight conditions, when there is a visual
reference to the horizon and ground, the sensory system in the
inner ear helps to identify the pitch, roll, and yaw movements
of the aircraft. When visual contact with the horizon is lost,
the vestibular system becomes unreliable. Without visual
references outside the aircraft, there are many situations in
which combinations of normal motions and forces create
convincing illusions that are difficult to overcome.
Prevention is usually the best remedy for spatial disorientation.
Unless a pilot has many hours of training in instrument flight,
flight should be avoided in reduced visibility or at night when
the horizon is not visible. A pilot can reduce susceptibility
to disorienting illusions through training and awareness and
learning to rely totally on flight instruments.