Vertical
wind is approximated using a simplified inversion of the aircraft equation of
motion (Kopp, 1985).An example is shown
in Figure 1 for Flight 813 on
The technique is valid only for straight and level, non-accelerating flight. The negative vertical windepisode in the figure above, beginning around 23:13 and continuing through 23:14, is actually during a turn, and the deduced vertical wind is not valid during this time interval. Basically, the pilot pitches the aircraft nose up and adds power during the turn to maintain altitude as the aircraft undergoes an acceleration to change horizontal direction, and the Kopp inversion infers a downdraft because the nose is pitched up but the altitude is not increasing as it should if the nose is pitched up in straight-line flight.