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MATHEMATICS FOR AIR CREW TRAINEES     38-39

[[image - drawing of a protractor showing the North Line and an angle of depression]]
FIGURE 44.

f. Angles of elevation and depression. -The angle of elevation or angle of depression of any given object is the angle made by the line to that object and a horizontal line at the eye level in the same vertical plane. In figure 45 the angle made with the two airplanes is the angle of elevation while the angle made with the power lines is the angle of depression.

[[image - drawing illustrating an angle of elevation and an angle of depression]]
FIGURE 45.

39. Course, heading, drift.-a. True course (C)-Direction over the surface of the earth expressed as an angle with respect to true north in which an aircraft intends to fly. It is the direction as laid out on a map or chart.

b. True heading (H).-Angular direction of the longitudinal (front to rear) axis of the aircraft with respect to true north.

c. Drift (D)-Angle between the true heading and the true course. It is right drift if the true course is greater than the true heading. If the true course is less than the true heading, it is left drift.

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