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2. Although a deterioration in night vision
occurs at a cabin pressure altitude as low as
5,000feet, other significant effects of altitude
hypoxia usually do not occur in the normal healthy
pilot below 12,000 feet. From 12,000 to 15,000 feet
of altitude, judgment, memory, alertness, coordination
and ability to make calculations are impaired,
and headache, drowsiness, dizziness and either a
sense of well‐being (euphoria) or belligerence occur.
The effects appear following increasingly shorter
periods of exposure to increasing altitude. In fact,
pilot performance can seriously deteriorate within
15minutes at 15,000 feet.
3. At cabin pressure altitudes above 15,000 feet,
the periphery of the visual field grays out to a point
where only central vision remains (tunnel vision). A
blue coloration (cyanosis) of the fingernails and lips
develops. The ability to take corrective and protective
action is lost in 20 to 30 minutes at 18,000 feet and
5to 12 minutes at 20,000 feet, followed soon
thereafter by unconsciousness.
4. The altitude at which significant effects of
hypoxia occur can be lowered by a number of factors.
Carbon monoxide inhaled in smoking or from
exhaust fumes, lowered hemoglobin (anemia), and
certain medications can reduce the oxygen‐carrying
capacity of the blood to the degree that the amount of
oxygen provided to body tissues will already be
equivalent to the oxygen provided to the tissues when
exposed to a cabin pressure altitude of several
thousand feet. Small amounts of alcohol and low
doses of certain drugs, such as antihistamines,
tranquilizers, sedatives and analgesics can, through
their depressant action, render the brain much more
susceptible to hypoxia. Extreme heat and cold, fever,
and anxiety increase the body's demand for oxygen,
and hence its susceptibility to hypoxia.
5. The effects of hypoxia are usually quite
difficult to recognize, especially when they occur
gradually. Since symptoms of hypoxia do not vary in
an individual, the ability to recognize hypoxia can be
greatly improved by experiencing and witnessing the
effects of hypoxia during an altitude chamber
“flight.” The FAA provides this opportunity through
aviation physiology training, which is conducted at
the FAA Civil Aeromedical Institute and at many
military facilities across the U.S. To attend the
Physiological Training Program at the Civil
Aeromedical Institute, Mike Monroney Aeronautical
Center, Oklahoma City, OK, contact by telephone
(405) 954-6212, or by writing Aerospace Medical
Education Division, AAM-400, CAMI, Mike
Monroney Aeronautical Center, P.O. Box 25082,
OklahomaCity, OK 73125.
NOTETo
attend the physiological training program at one of the
military installations having the training capability, an
application form and a fee must be submitted. Full
particulars about location, fees, scheduling procedures,
course content, individual requirements, etc., are contained
in the Physiological Training Application, Form
Number AC 3150-7, which is obtained by contacting the
accident prevention specialist or the office forms manager
in the nearest FAA office.
6. Hypoxia is prevented by heeding factors that
reduce tolerance to altitude, by enriching the inspired
air with oxygen from an appropriate oxygen system,
and by maintaining a comfortable, safe cabin
pressure altitude. For optimum protection, pilots are
encouraged to use supplemental oxygen above
10,000 feet during the day, and above 5,000 feet at
night. The CFRs require that at the minimum, flight
crew be provided with and use supplemental oxygen
after 30 minutes of exposure to cabin pressure
altitudes between 12,500 and 14,000 feet and
immediately on exposure to cabin pressure altitudes
above 14,000 feet. Every occupant of the aircraft
must be provided with supplemental oxygen at cabin
pressure altitudes above 15,000 feet.
b. Ear Block.
1. As the aircraft cabin pressure decreases
during ascent, the expanding air in the middle ear
pushes the eustachian tube open, and by escaping
down it to the nasal passages, equalizes in pressure
with the cabin pressure. But during descent, the pilot
must periodically open the eustachian tube to
equalize pressure. This can be accomplished by
swallowing, yawning, tensing muscles in the throat,
or if these do not work, by a combination of closing
AIM 2/14/08
8-1-4 Fitness for Flight
the mouth, pinching the nose closed, and attempting
to blow through the nostrils (Valsalva maneuver).
2. Either an upper respiratory infection, such as
　
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