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You are on a VFR flight and the traffic circuit altitude of your destination has to be established 5 NM before reaching the aerodrome. Given:

Ground Speed: 130 kts
Cruising altitude: 4 500 ft AMSL
Traffic circuit altitude: 2 500 ft AMSL
Rate of descent: 500 ft/min

Calculate the shortest distance from the destination where you must initiate the descent.

  • A
    20 NM
  • B
    14 NM
  • C
    25 NM
  • D
    9 NM

The aircraft descends from cruise altitude 4500ft to the traffic pattern altitude 2500 ft, thus the height difference is: 4500 ft - 2500 ft = 2000 ft.

The aircraft's average Rate of Descent is 500 ft/min, which means that it loses 500 ft in 1 min. Therefore, the aircraft loses 2000 ft in: 2000ft / 500 ft/min = 4 minutes.

The aircraft flying with a Groundspeed of 130 kt, in 4 minutes will cover a distance of: 130 kt x 4/60 hr = 8.67 NM.

But, since the traffic circuit altitude of the destination has to be established 5 NM prior to the destination aerodrome, the descent must be initiated: 8.67 NM + 5 NM = 13.67 NM, or rounded 14 NM before the destination aerodrome.

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