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QID 310481 - Definition of Useful Load

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  • QID 310481 - Definition of Useful Load

    The following message was originally sent by email to support@bristol.gs on June 2nd, 2018. I was requested to post this message on the ATP Forum.


    Dear Bristol Support,

    Regarding ATPL(A) Mass & Balance question ID 310481, two given options are:

    A) ZFM is 2579 lbs and the Useful load is 1057 lbs (marked as the correct answer)
    B) ZFM is 2579 lbs and the Useful load is 1075 lbs (this is the truly correct answer)

    The difference in useful load between options A) and B) is the taxi fuel, equal to 18 lbs. As taken by your explanation you define useful load as being the sum of traffic load and take-off fuel (thus not including taxi fuel in this definition).

    However, CAP 696 defines useful load as:

    ​Useful Load - is the total mass of the passengers, baggage and cargo, including any non-revenue load and usable fuel​.
    ​It is the difference between the Dry Operating Mass and the Take-Off Mass.

    This definition by CAP 696 is "in italics", meaning that the definition is not given in ICAO, JAA or EASA but is in "common use". I find it frankly quite alarming that the EASA exams rely on definitions that aren't even defined by EASA themselves but are assumed to be "common knowledge"! Surely a term such as "useful load" requires a formal and official definition if it is being asked in an official exam.

    CAP 696 contradicts itself in that it first includes "usable fuel" in the definition of useful load but then states it's the difference between DOM and TOM, hence now not including the taxi fuel.

    Taxi fuel is clearly part of the usable fuel as usable fuel is any fuel that is in the tanks of the aircraft and can be consumed, prior to starting the engines. Usable fuel = Total fuel on board - Unusable fuel.

    Why do you choose to use the UL=TOM-DOM definition instead of updating it to what the CAP 696 in essence is trying to say, which is UL = TM - DOM, where TM is the taxi or ramp mass. This way the taxi fuel would be included in the useful load which is what I believe makes the most sense.

    Kind regards,

  • #2
    The answer to this question is perfectly correct. Regarding the ZFM the answer of 2579 lbs is correct. The useful load is 1057 lbs. Your statement that 1075 is the truly correct answer is incorrect! The sweeping statement that confirms this is that the Useful Load is the difference between the DOM and the TOM. This infers you do not include the start up and taxi fuel as part of the useful load. Yes arguably you need S & T fuel on board allowing you to start all of your engines and get to the runway, however in aviation terms it is fuel wasted in so far as it isn't getting you to your destination and earning you money, it's costing you money and if it's a long taxi even more so. Your trip fuel and reserves are there to get you from A to B i.e. take-off to landing at your destination. In the CAA exams, if you include S & T fuel in your useful load calculations you would be incorrect and lose easy marks.

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