Information Sheet No. 4.5.1I
The path of an aircraft over the earth's surface is determined by two factors: (1) direction of
the aircraft through the air mass and (2) direction of the air mass across the earth's
surface. The motion of the air mass is called wind. This assignment will aid in
understanding the effects of wind on an aircraft's flight path.
Wind is the movement of an air mass across the earth's surface. Its direction is expressed
as the direction from which the wind blows in degrees true (i.e., the origin of the wind). For
example, a 045 wind is a wind originating from the northeast and blowing toward the
southwest. The wind's velocity is always given in nautical miles per hour (knots).
Winds are reported in one of two ways: TRUE winds and MAGNETIC winds. En route
winds received from the forecaster are TRUE winds and are taken from the Winds-Aloft
Charts and Teletype Winds-Aloft Forecasts. The surface winds received from Airport
Traffic Control Towers and Approach/Departure Control are MAGNETIC winds that
coincide with the magnetic direction of the runways.
The Wind Side of the CR-3 circular computer is designed to aid the Warrior-Navigator in
the solution of wind problems. The Wind Side of the CR-3 can be used to solve for
navigation problems with the use of Ground Speed, courses, and distances.
Think of the air mass as a large balloon. If an aircraft is inside the balloon, it may travel at
any speed and in any direction. As long as the balloon does not move over the ground, the
aircraft's motion (speed and direction) over the ground is the same as its motion inside the
balloon. Once the balloon begins moving, however, the aircraft's motion over the ground is
a combination of its motion inside the balloon and the motion of the balloon over the