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PPL · EASA 061 · Dead reckoning navigation
Leg time from ground speed
Your TAS is 120 kt and the wind gives you a ground speed of 105 kt. How long does a 42 NM leg take?
Optional: check your working step by step.
Explanation
Time over the ground depends on ground speed, not on airspeed: the wind is carrying the whole air mass, and you with it. Divide the distance (d) by the ground speed (GS) and turn the time (t) from hours into minutes.
Step by step
- Use ground speed: 105 kt.
- Time in hours: 42 NM ÷ 105 kt = 0.4 h.
- In minutes: 0.4 × 60 = 24 min.
Why not the other answers
- 21 min uses the true airspeed, TAS (42 ÷ 120 = 0.35 h). The aircraft moves 120 kt through the air, but only 105 kt over the ground.
- 40 min reads 0.4 h as 40 minutes. An hour has 60 minutes, so 0.4 h is 24 minutes.
- 150 min turns the division upside down: 105 ÷ 42 = 2.5 h, that is 150 min.
Tip. Quick check: at 105 kt you cover 1.75 NM per minute, so 42 NM takes 24 minutes. On the navigation computer, set the ground speed against the 60 index and read the time under the distance.
Original questions written by FlightDesk Aero and aligned with the EASA syllabus. They are not questions from the official EASA exam bank.