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You are flying along an airway which is 10 NM wide (5 NM either side of the centreline). The distance to the VOR/DME you are using is 100 NM. If you are on the airway boundary, how many dots deviation will the VOR needle show if one dot represents 2 degrees?
  • A
    1.5
  • B
    4.5
  • C
    3.0
  • D
    6.0

Refer to figure.
As seen in the figure, the aircraft is on the airway boundary which is 5 nm form the intended course. The CDI therefore will show a deflection to the right since the selected course will be directly inbound to the station.

The distance that DME shows 100 nm. Which should be the hypotenuse, but for the such distance, we can approximate that the distance from the airway is the same.

To calculate the angle of deflection the aircraft has relative to the intended course we can use the following formulae:
Tangent (correction angle) = (Distance off intended track)/(Distance to go) = (5nm)/(100nm) = 0.05

Tan -1(0.05) = 2.86° = 3°

If one dot represents 2° then 3° will be equal to:

1 dot2°
?3°

? = (3° x 1 dot)/(2°) = 1.5 dots

1:60 solution:
• Track Error Angle = (dist off-track × 60) ÷ dist along track
• TEA = (5 NM × 60) ÷ 100 NM
• TEA = 3°

If one dot represents 2° then 3° will be equal to: 1.5 dots

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