Information Sheet: Preflight Winds

INFORMATION SHEET

Preflight Winds

Information Sheet No. 4.5.1I

INTRODUCTION

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.

REFERENCES

INFORMATION

WIND THEORY

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

ground.

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