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Explanation - QB ID: 320386

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  • Explanation - QB ID: 320386

    The Explanation for QB ID: 320386 is confusing (at least for me). It starts out by converting the 100 KIAS into TAS and GS then calculates the "Still Air Distance" as 14948ft. (No issues up to that point!). However, it goes not continue to calculate the "Ground Distance" using the formula in CAP 698 para 3.2.3 (e) which outlines "Ground Distance = Still Air Dist x GS/TAS" (14948 x 113/108 = 15640ft - the correct answer shown in the QB).

    Instead the Explanation states that "The CQB answer is clearly wrong" and then proceeds to "prove this by taking the ROC from the graph 1080 fpm" to work out the "Ground Dist" - a rather complex method that includes conversions from ft>nm>ft. Was this calculation necessary to arrive at the "close enough" answer or is it just another (complex) method? This does not appear to be consistent with the Explanation given in QB ID: 320385 or the example in CAP 698 where the same formula ("Ground Distance = Still Air Dist x GS/TAS") is used . Am I missing something here????

    Appreciate any assistance in clarifying this.


  • #2
    No idea what's happened here but have corrected the explanation so that it uses the formula same as 320385.


    • #3
      I can't understand why it's necessary to go to the the lengths of working out the climb gradient in this question.
      Why can we not take the height to be gained, 1450 ft divide that by the ROC, which by my calculation from the graph comes to 1100 ft /min
      1450/1100 = 1.31818 mins and then multiply that by the ground speed in ft/min
      GS is TAS 108 min + TW 5kts = 113 kts
      (113/60) x 6080 x 1.31818 = 15094 ft
      My next question is why is this answer so different to that given as the correct answer.
      The less interrogation of the graphs the better in my mind, as there is more to go wrong, but why are the answers so different?