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While doing the “Mass and Balance” subject for the EASA ATPL, I came around two useful load definitions which contradict itself. The first definition says:

The Useful Load is the total mass of the passengers, baggage and cargo, including any non-revenue load and usable fuel.

By saying usable fuel I assume that it includes taxi fuel + takeoff fuel, but then in the other definition they say about the All Up Mass (AUM):

The AUM in the diagram above refers to the mass of the aircraft at Take-Off because the Useful Load is always determined with reference to the aircraft mass with Take-Off Fuel on board.

Here’s the diagram for reference: enter image description here

Which one is correct?

If you could give me official sources for it I would appreciate :)

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Yes, the useful load includes taxi fuel.

Both definitions are correct and do not contradict each other:

The Useful Load is the total mass of the passengers, baggage and cargo, including any non-revenue load and usable fuel.

This statement is true. Think of useful load as anything that’s not part of the actual aircraft. You specifically mentioned taxi fuel and takeoff fuel, which are both usable fuel and included, but then added a second quote:

The AUM in the diagram above refers to the mass of the aircraft at Take-Off because the Useful Load is always determined with reference to the aircraft mass with Take-Off Fuel on board.

Your question insinuates that there is a contradiction between the two because the second definition excludes taxi fuel.

While it is true that the second definition includes takeoff fuel only, it is not because the definition of useful load is any different, it is simply because once you are at the hold short and ready for takeoff any fuel you planned to use for taxi has already been burned!

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  • $\begingroup$ Thank you, it does make sense now :) Are there any official source, like from ICAO or EASA, where they specifically say that? $\endgroup$
    – n00b
    Commented Aug 7, 2023 at 18:24
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    $\begingroup$ Where they specifically say what? That you use up taxi fuel when you taxi? You can't takeoff with taxi fuel because by definition you are no longer taxiing. Fuel is fuel at that point, it isn't stored in separate tanks... (don't overthink this!) $\endgroup$
    – Michael Hall
    Commented Aug 7, 2023 at 18:29
  • $\begingroup$ You’re right, I tend to overthink sometimes… I just wanted an official source from that definition “useful load” $\endgroup$
    – n00b
    Commented Aug 7, 2023 at 18:59
  • $\begingroup$ Where did that first definition come from? Because it says all usable fuel is included. That covers all fuel except UNusable fuel. $\endgroup$
    – Michael Hall
    Commented Aug 7, 2023 at 19:40
  • $\begingroup$ From Mass and Balance Padpilot book $\endgroup$
    – n00b
    Commented Aug 7, 2023 at 20:20

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