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During public awareness campaign in schools, students always want
clarification on the subject of "potholes in the sky".
Inside a thick cloud there is usually upward
and downward movement of air. The hailstones that fall when
a big storm passes actually grow in the upper part of these
clouds where wind speeds can reach up to 50 metres per
second. If an aircraft enters a long cloud band such as the
Inter-Tropical Convergence Zone (ITCZ), which is associated
with the rainy season, it will experience turbulence and
will move up and down in response to the upward and downward
forces inside the cloud. As a safety measure, the Captain of
the aircraft will normally announce in person or through
cabin crew for passengers to fasten their seat belts. These
are the conditions when passengers without fastening the
seat belt have been reported to hit the ceiling of an
aircraft.
The up and down movement of the aircraft
creates an impression of "potholes in the sky". These
conditions can also be encountered under clear skies if the
wind direction suddenly changes or if wind speeds are too
strong.
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