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Questions 320419 and 320385

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  • Questions 320419 and 320385

    I have been tutoring a student on Aeroplane Performance, and helping with the above questions he was stuck on, but I get a different answer, although my method was only very slightly different. I was wondering how confident you are of the wording of the question and that the answers in the ECQB are as you have shown?

    For the first one, 320419, you have assumed that the lower altitude of 4000 feet is an aerodrome and so started the climb at screen height, although as written the question mentions only a climb from 4000 feet to 5500. In CAP698 this graph is in a topic labelled "take off climb", but the graph is actually suitable for any climb at 100 KIAS and that label would not be included in an exam annex, as the graph is only labelled "climb".

    In addition you have used the TAS and rate of climb at 4000 feet to calculate the distance covered. While TAS and RoC do not change much over 1500 feet, it is significant in the context of the question with answers around 1500 feet apart. To find the distance covered more accurately some estimate of average rate of climb and TAS should really be used, and difference in gradient is enough to change bring the answer closer to 21000 feet than 19500.

    Question 320385 does mention an airfield so the screen height is implied, but is still calculated using the performance data for the bottom of the climb.

    Now I have taught General Navigation and Flight Planning far more than Performance, so am using the methods recommended for climb and descent questions in those subjects. It is entirely possible that there are different recommendations for answering Performance questions.

  • #2
    Does anyone else have any ideas on this one? Anyone come across this in the real exam, and know they got the answer right?

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    • #3
      Bumping this up, I'm having the same basic issue with these questions

      Answers are all pretty close from one another, and given the difference in altitude between bottom and top of climb, there is a noticeable drop in climb rate at ToC, and increase in TAS.
      By using the average value at 2/3 of the climb, it is just enough to get bang-on another answer than the one flagged correct.

      Why would the examiner dismiss the precise way in favour of an approximate one in this case, and what are the clues one could have to tell which method to use if a similar question shows up during an exam ?

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      • #4
        Also bumping this up (Q320385)...

        The answers seem far too close together. As per the above posts, the small changes in TAS throughout the climb are enough to make noticeable differences in the final answer. I also get a TAS of 104kts, not 103kts, which is enough to make significant differences to the final answer.

        Furthermore, working out the answer using the vertical speed of 1120 ft/min instead of the gradient gives:

        1950 / 1120 = 1.74107 mins

        Converting this to a ground distance:

        (1.74107 / 60) * (103-15) = 2.5535714 nm = 15,525 ft

        Where I've converted to hours in the first bracket, and multiplied by GS (TAS=103kts - 15kts headwind). This is actually probably close enough to work out the accepted answer of 15,400 ft, but the point still stands that the answer obtained is extremely sensitive to the method used. In fact, the above used the 'accepted' TAS of 103kts. If one uses 104kts I get 15,702ft. We're now nearly halfway between two of the answers...

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