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An aircraft cruising with a true airspeed (TAS) of 180 kt was initially planned to arrive at a waypoint at 16:25. At 15:25, ATC instructs the pilot to adjust the arrival time at the waypoint to 16:55. If there is a 20 kt tailwind, what new groundspeed should the pilot maintain to meet the revised arrival time?

  • A

    100 kt

  • B

    133 kt

  • C

    123 kt

  • D

    113 kt

EASA LO 061.01.05.04.06: Calculate revised GS to reach a waypoint at a specific time.

First, we can calculate the original groundspeed. We are flying with a TAS of 180 kt, in a 20 kt tailwind → our original GS is 200 kt.

We can then calculate the distance to the next waypoint - at 15.25, we expect to arrive at the next waypoint at 16.25 which is in 1 hour.
Distance to go = speed x time = 200 kt/1 hr = 200 NM

Our revised time of arrival is now 16.55, another 30 mins. The distance to go is still 200 NM, but we need to fly for 16.55 - 15.25 = 1 h 30 min.

The new groundspeed = distance/time = 200/1.5 = 133 kt

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