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Pilot's Handbook of Aeronautical Knowledge
Aeromedical Factors

Health and Physiological Factors Affecting Pilot Performance

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




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.

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 do.

A third-class medical certificate is required for a private or
recreational pilot certificate. It is valid for 3 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 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 3 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 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.

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 means "reduced oxygen" or "not enough oxygen."
Although any tissue will die if deprived of oxygen long
enough, usually the most concern is 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. The forms of hypoxia are
based on their causes: hypoxic hypoxia, hypemic hypoxia,
stagnant hypoxia, and 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 the airplane 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.

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
(due to 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 on page
16-11. Hypemic hypoxia can also be caused by the loss
of blood due to blood donation. Blood 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.