When computing weight and balance, what does the empty weight of an aircraft include?

The empty weight of an aircraft is defined as the weight of the airframe, engines, and all items considered fixed or permanently installed in the aircraft. This encompasses not only the airframe and engines but also includes all unmovable equipment, unusable fuel, hydraulic fluid, and undrainable oil. Unusable fuel is fuel that cannot be drawn for use during operation due to the design of the fuel system, and other fluids such as hydraulic fluid and oil are necessary for the operation of certain systems within the aircraft.

This definition aligns with industry standards and regulations regarding weight and balance calculations, ensuring safety and operational efficiency. Properly computing empty weight is crucial for flight planning, as it forms the basis for understanding how much payload (including passengers and cargo) can be added while adhering to the aircraft's weight limits.