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It should be noted that rotation of the body is detected by the fluid in the semi-circular canals of the inner
ear, and this tells us when we change angular position. However, in the absence of a visual reference,
such as flying into a cloud, the rotatory accelerations can be confusing, especially since their forces can
be misinterpreted as gravitational pulls on the muscles and otoliths. The result is often disorientation.
Pilots should have an instructor demonstrate manoeuvres which will produce disorientation. Once
experienced, later unanticipated incidents of disorientation can be overcome as long as instruments (for
pilots trained to use them) or reliable ground references are available. Such a demonstration will show
you how confusing the false inputs from the inner ear can be.
Pilots are susceptible to experiencing disorientation at night, and in any flight condition when outside
visibility is reduced to the point that the horizon is obscured. An additional type of vertigo is known as
flicker vertigo. Light, flickering at certain frequencies, from four to twenty times per second, can produce
unpleasant and dangerous reactions in some persons. These reactions may include nausea, dizziness,
unconsciousness, or even reactions similar to an epileptic fit. In a single engine propeller aeroplane
heading into the sun, the propeller may cut across the sun to give this flashing effect, particularly during
landings when the engine is throttled back. These undesirable effects may be avoided by not staring
directly through the propeller for more than a moment, and by making frequent but small changes in
RPM. The flickering light traversing helicopter blades has been known to cause this difficulty, as has the
reflection from rotating beacons on aircraft while flying in clouds. If the beacon is bothersome, shut it off
during these periods, advise air traffic control and remember to turn it back on when clear of clouds.
Carbon monoxide
Carbon monoxide (CO) is a colourless, odourless, tasteless product of an internal combustion engine and
is always present in exhaust fumes. Even minute quantities of carbon monoxide breathed over a long
period of time may lead to dire consequences.
For biochemical reasons, carbon monoxide has a greater ability than oxygen to combine with the
haemoglobin of the blood. Furthermore, once carbon monoxide is absorbed in the blood, it sticks “like
glue” to the haemoglobin and actually prevents oxygen from attaching to the haemoglobin.
Most cockpit heaters in light aircraft work by air flowing over the exhaust manifold. So if you have to use
the heater, be wary if you smell exhaust fumes – there may be a leak from the engine exhaust pipe into the
air used for cockpit warming. The onset of symptoms is insidious, with “blurred thinking”, a possible
feeling of uneasiness, and subsequent dizziness. Later headache occurs. Immediately shut off the heater,
open the air ventilators, descend to lower altitudes, and land at the nearest airfield. Consult a designated
medical examiner for advice. It may take several days to fully recover and clear the body of the carbon
monoxide. Use carbon monoxide detectors in the cockpit, since affected pilots may otherwise be
completely unaware that they are being exposed to CO.
Vision
Reduced or impaired vision can be critical. To avoid eye fatigue in bright light, use colour-neutral (rather
than coloured) sunglass lenses as this will permit normal colour discrimination. If you need to use
correcting lenses for good vision make sure you keep a spare pair of spectacles within easy reach, so that
you can easily find them if you if you lose or break your first pair, or develop problems with contact
lenses. Visit an eye care specialist if you notice a change in visual acuity.
ICAO Preliminary Unedited Version — October 2008 V-2A-4
Middle ear discomfort or pain
Certain persons (whether pilots or passengers) have difficulty balancing the air pressure on either side of
the ear drum while descending. Sometimes pressure equalization can occur at different times in each ear,
resulting in a form of disorientation named ‘alternobaric vertigo’. Problems arise if a head cold or throat
inflammation keeps the Eustachian tube from opening properly. If this trouble occurs during descent, try
swallowing, yawning, or holding the nose and mouth shut and forcibly attempting to exhale (Valsalva
manoeuvre). If no relief occurs, climb back up a few thousand feet (if feasible) to relieve the pressure on
the eardrum. Then descend again, using these measures. A more gradual descent may be tried, and it may
be necessary to go through several climbs and descents to “stair step” down. If a nasal inhaler is available,
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Manual of Civil Aviation Medicine 2(161)
