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PPL · EASA 061 · Dead reckoning navigation
Maximum drift with the 1 in 60 rule
TAS 100 kt. The wind blows at 20 kt exactly at right angles to your track. Using the 1 in 60 rule, roughly how much drift should you expect?
Optional: check your working step by step.
Explanation
A wind at right angles to the track gives the largest drift you can get from it, the maximum drift (MD). TAS is the true airspeed and WS the wind speed. The 1 in 60 rule turns it into one line of mental arithmetic: in one hour you fly 100 NM through the air and the wind pushes you 20 NM sideways, and 1 NM off after 60 NM is 1°.
Step by step
- 60 ÷ TAS: 60 ÷ 100 = 0.6.
- Times the wind speed: 0.6 × 20 = 12°.
- Check with trigonometry: arcsin(20 ÷ 100) ≈ 11.5°, so the rule is close enough for the cockpit.
Why not the other answers
- 20° takes the wind speed in knots as degrees of drift. That only works when the TAS is 60 kt.
- 5° divides TAS by wind speed (100 ÷ 20). The drift grows with the wind, so the wind speed belongs on top.
- 6° halves the result as if the wind were only 30° off the track. Here it blows at 90°, so you get the full maximum drift.
Tip. For a wind at an angle, take a fraction of the maximum drift with the clock rule from the crosswind article: 30° off gives about half, 45° about three quarters, 60° or more almost all of it.
Original questions written by FlightDesk Aero and aligned with the EASA syllabus. They are not questions from the official EASA exam bank.