Mass and Balance
Mass and Balance tests mass terms, CG calculation, datum/arm/moment, MAC limits, and loading effects. The exam expects clean arithmetic and unit discipline.
Terms and limits
BEM (basic empty mass) includes unusable fuel and oil; DOM adds crew and usable fuel; ZFM is zero-fuel mass; TOM is take-off mass; LM is landing mass. CG must stay within forward and aft limits; forward limit affects rotation and stall margin, aft limit affects stability.
Worked example
Items: 1000 kg at arm 2.0 m and 500 kg at arm 3.0 m. Moments: 2000 + 1500 = 3500 kg·m. Total mass 1500 kg. CG = 3500 / 1500 = 2.33 m from datum. If the aft limit is 2.30 m, the load is out of limits and must be redistributed forward.
Fuel and MAC
Fuel burn shifts CG as fuel leaves tanks; calculate landing CG separately. MAC percentage = (CG − LE MAC) / MAC length × 100. Use the correct datum and sign for arms ahead of the datum.
Traps
Adding arms instead of moments; using kg and lb inconsistently; forgetting zero-fuel mass; ignoring that fuel has an arm; rounding before the final step.