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A helicopter is flying at 5000 ft and the ATC instructs the Pilot to descent to 3500 ft and report at a waypoint 5 NM away. What is the required rate of descent and descent time needed, if during the descent the TAS is 140 kt and the headwind 20 kt?

  • A

    600 fpm; 2 min and 49 seconds

  • B

    700 fpm; 2 min and 50 seconds

  • C

    600 fpm; 2 min and 30 seconds

  • D

    700 fpm; 2 min and 30 seconds

Rate of descent (ROD) is a vertical speed and represents the rate of decrease of the vertical height per unit of time, usually expressed in feet per minute (ft/min):

1. The helicopter descends from 5000 ft to 3500 ft, thus the height difference is: 5000 ft - 3500 ft = 1500 ft.

2. The helicopter descends with a headwind component of 20 kt, thus its Groundspeed will be: 140 kt - 20 kt = 120 kt.

3. The flight time during the descent is: Ground distance / GS = 5 NM / 120 kt = 0.042 hr or 2.5 min or 2 minutes and 30 seconds.

4. Therefore, its Rate of Descent must be: ROD = Height difference / Flight time = 1500 ft / 2.5 min = 600 ft/min.

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