40odd2 --
The history is as I said. Fuel is sold by mass (kg) and the energy value of the fuel is adjusted in the refinery to meet a specified range of specific energy values (MJ/kg, or kWh/kg, for example). What the pilot needs to know is how much energy he has in his tanks (just as applicable to gasoline as to gas turbines) and the mass he is carrying, for MTOW and COG calculations, for example. Litres is a unit that serves the pilot no use. Just work in kg and convert all non-kg values to kg. It's not something the pilot can just elect to do, or any manufacturer, and it's unlikely to be anything to do with this accident....but it would help safety by reducing the number of calculations the pilot has to do.