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An aircraft is being flown in the cruise. Determine the expected drift, given:

Course: 210°(M)
TAS: 179 kt
Forecast wind: 330°/50 kt
Variation: 20°W

  • A

    16° left

  • B

    14° left

  • C

    10° left

  • D
    8° left

Refer to figure
To solve this exercise, we must ensure that all directions are either in True or Magnetic. We can accomplish this by either converting the course to True or changing the wind to Magnetic.

We can use the mnemonic:
"Magnetic Variation East, Magnetic Least; Magnetic Variation West, Magnetic Best"

In this case, we've decided to convert the course to True:

Course 210º (M), Variation 20ºW
210º(M) - 20ºW = 190º (T)

Using the flight computer to determine drift, remember that we are using a track, not a heading.

  1. Place the center of the rotating disk on the value representing the true airspeed (179 knots).
  2. Position the wind direction (330º) under the true index.
  3. Mark the wind velocity (50 knots) upwards from the center.

Note: When the question provides a track, mark wind velocity upwards from the center. When the heading is known, mark wind velocity downwards from the center.

  1. Align your true track (190º) under the true index.
  2. Slide the wind velocity mark to True Air Speed (179 kt).

The Wind Correction Angle (WCA) is read between the centerline and the wind velocity mark, which indicates a 10º right correction (+10º). WCA and drift are opposite in direction and of equal magnitude. So, a WCA of 10ºR corresponds to a drift of 10ºL.

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