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  • Question 330768 help!

    Fuel penalty question.
    The correct answer is listed as 22781 kg.
    The question gives two different fuel penalties, one "based on TOM" which is +166kg and one "based on LM" which is +199kg.
    Interestingly, I worked it out using the +166kg figure and got the same answer.
    Can someone please clarify why you have used the one based on landing mass? Is it because the landing mass is the limiting mass (19000kg)?.
    Could someone also check my working?

    Calculating penalty "based on TOM" of +166kg
    Penalty is 166kg per 1000kg extra fuel.
    Therefore useful remaining on board would be 834kg (1000-166).
    Penalty ratio is 834/1000 = 0.834.
    To calculate how much ADDITIONAL fuel we can uplift based on this, I use one of two methods, either this formula:

    Maximum fuel uplift = remaining landing mass available / penalty ratio
    i.e. Maximum fuel uplift = 19000kg / 0.834 = 22781kg.

    or else I reason it out

    19000kg = 83.4%, therefore what is 100%?
    100 x 19000 / 83.4 = 22781kg.



    This method gives the correct answer in this question, and also the other fuel penalty question.


    BUT

    I cannot understand the reasoning given in the explanation of this question, which uses the "based on landing mass" figure of +199kg.
    Using this figure and either of the two methods above, the answer would be 23720kg

    It does not really matter if you get to select the answer, but for type in, it might be a problem.


    Can someone please clarify why the 199kg was used, and the reasoning behind the calculationg method used in the explanation? (19000 / 1000 x 199).

    Thanks!

  • #2
    Hi Transalp

    Both methods work on ratios but the new EASA style of giving corrections for LDM and TOM reflect the last minute change corrections on Operational Flt Plans currently in use.

    Essentially if given only one correction 250 Kg / 1000 = 750 kg at landing for every 1000 kg extra at T/O;then we use that ratio for calculations:
    If TOM is limiting mass but we need to find either additional mass at landing or fuel penalty then Additional fuel at T/O x 0.75 = Additional Mass at landing.
    If LM limited then additional LM fuel divided by 0.75 will give additional fuel at T/O.

    If given fuel penalties TOM + 166 Kg and LM +199 then they must be used in the following manner to achieve the correct answer.

    In this case LM limited so for every additional 1000 kg at landing 199 Kg were burnt in transit (fuel penalty). 19000 Kg additional fuel at landing;Therefore 19 x 199 Kg = 3 781 Kg
    19 000 Kg at landing + Fuel Penalty = 22 781 additional fuel at T/O including fuel penalty.
    Do not forget to cross check this against MTOM and Tank capacity.

    If TOM limited but need to find the Fuel Penalty and/or the additional mass at landing then for each additional 1000 kg at T/O the aircraft will burn 166 Kg.
    So to find fuel penalty multiply the additional fuel by 166 Kg to find the fuel penalty and subtract that from the additional fuel at T/O to find additional fuel at landing.
    In this case 22 781 Kg additional at T/O. 22.78 x 166 = 3 781 Kg . The same fuel penalty calculated from the LM limitation.

    Do not mix methods or you may not achieve the answer required.

    Mac
    BGS TKI

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    • #3
      Mac Thank you so much - that makes more sense. Sorry for bombarding you with questions

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