Refer to figure.
First Step: Determine the Useful Load (UL)

The UL equals the sum of Traffic Load (TL) and the Take-off Fuel (TOF). Consequently, the useful load is the difference between the Take-off Mass and the Dry Operating Mass:

• Useful Load = TOM - DOM
  Useful Load = 5980 kg – 4830 kg = 1150 kg

Second Step: Determine Take-off fuel mass.
The conversion between fuel volume and mass is very simple: fuel volume in litres × Specific Gravity (density) = fuel mass in kg.
• 770 l × 0.782020 => 602 kg

Third Step: Determine the Traffic Load (TL)
The TL will be equal to the difference between the Useful Load (UL) and the Take-off Fuel (TOF).

• Useful Load (UL) = TL + TOF
  Traffic Load (TL) = UL – TOF
• Traffic Load (TL) = 1150 kg – 602 kg = 548 kg