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While cross-referencing the map during a flight, the pilot notices that one of the waypoints has been missed by 1.20 NM off-track. The helicopter is flying with a TAS of 120 kt and the last waypoint was correctly overflown 22.5 minutes ago. How many degrees off-track had the helicopter been since the last waypoint?
  • A

    1.60°

  • B

    1.20°

  • C

    1.11°

  • D

    0.45°

Refer to figure.
This question asks for the Track Error Angle (TKE), the angle difference between the track made good and the required track, and can be solved either by using your Flight/Nav computer or applying the "1:60 rule":

  • Flight/Nav computer method:
  1. Rotate the inner disc until the distance travelled: TAS x Time = 120 kt x 22.5/60hr = 45 NM (45) is below the distance off-track 1.2 NM (12).
  2. Above the black arrow, read the TKE, 1.60°.
  • "1:60 rule" method:

Distance off track x 60 / Distance along the track = Track Error Angle (TKE)

1.2 NM x 60 / 45 NM = 1.6°

Every 1 NM off-track at 60 NM equates to 1º TKE. So, 1.2 NM off-track at 45 NM equates to 1.60° TKE.

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