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What is the required horizontal distance, measured from an airfield at sea level, to initiate a descent from an altitude of 17 000 ft and reach an altitude of 2000 ft while being 10 NM away from the airfield? The descent rate is set at 1500 ft/min, and the ground speed is 180 kt.

  • A

    60 NM

  • B

    30 NM

  • C

    40 NM

  • D
    50 NM

The aircraft is currently at 17 000 ft and is required to descend to 2 000 ft which means that it must descend 15 000 ft.

With a rate of descent of 1500 ft/min, the aircraft will take 10 minutes to descend 15 000 ft (15 000 ft ÷ 1500 ft/min).

We must now calculate the distance the aircraft will cover in 10 minutes when flying at a GS of 180 kt: (180 kt x 10 min) ÷ 60 min = 30 NM

Since the aircraft should reach 2 000 ft at 10 NM from the airfield, it should start descent at a minimum distance of 40 NM (30 NM + 10 NM).

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