Consider the following scenario. Preflight planning for the leg from point A to point B
produces a TC of 055T for a distance of 120 nm (Figure 4.6-2). The preflight wind
calculation yields a TH of 052T and a predicted GS of 255 kts. Once in the air the aircrew
sets a TH of 052T and a TAS of 250 kts and proceeds on his merry way. 15 minutes into
the leg the aircrew fixes his position at point C in Figure 4.6-2. Using plotting skills learned
in chapter 2, a track of 045T and a distance of 55 nm is measured. A quick time, speed,
distance calculation reveals a ground speed of 220 knots.
Figure 4.6-2 Wind Scenario (not to scale)
Since the Track (045T) and actual Ground Speed (220 kts) are different from the True
Course (055T) and predicted Ground Speed (255 kts), it becomes evident that actual
winds are different from the forecast winds. Now, there is enough information to construct
two of the three vectors of the wind triangle, the Air and Ground vectors (Figure 4.6-3), and
solve for the actual winds using the CR-3 computer.