What type of fuel is accounted for in the useful load calculation?

The useful load calculation in aviation involves the consideration of the total weight that an aircraft can carry, which includes passengers, cargo, and fuel. When it comes to fuel, only the usable fuel is factored into this calculation. This is because usable fuel represents the amount of fuel that can be effectively utilized by the aircraft during flight, impacting its performance, range, and operational safety.

Unusable fuel, on the other hand, refers to the fuel that cannot be drawn from the tanks due to design limitations or factors such as fuel tank configuration. Since this portion of fuel does not contribute to the aircraft's operation, it is not included in the useful load calculation.

In this context, hydraulic oil is irrelevant to the useful load as it involves a different aspect of aircraft systems and operations. Thus, the correct approach in calculating useful load focuses solely on the weight of the usable fuel, as this directly affects the aircraft's performance and loading capacity during flight operations.