Weight and Balance
The Weight and Balance domain tests the arithmetic and airmanship of loading: calculating CG from moments, checking limits at takeoff, landing and zero fuel, and recognising how fuel burn or a weight shift moves the CG.
Core rules
- Moment = weight × arm about the datum. CG = total moment / total weight.
- Check the CG against forward and aft limits for every relevant condition: basic empty, zero fuel, takeoff, landing.
- Adding weight at arm a: new CG = (old W × old CG + w × a)/(W + w). Moving weight: CG shift = (weight moved × distance moved)/total weight, toward the direction of the move.
- Respect MTOW, MLW, MZFW and maximum floor loading, not just the CG.
Worked example
Empty 800 kg at 2.00 m; pilot 80 kg at 2.40 m; baggage 20 kg at 3.00 m. Moments: 800×2.00 = 1600; 80×2.40 = 192; 20×3.00 = 60. Total = 1852 kg·m. Weight = 900 kg. CG = 1852/900 = 2.058 m. With limits 1.95–2.15 m the load is legal. If baggage rises to 40 kg, CG = (1600+192+120)/920 = 2.078 m: still legal but closer to the aft limit and less stable.
Traps
- Mixing kg with lb or cm with m.
- Using basic empty weight instead of zero-fuel weight.
- Forgetting that fuel burn changes both weight and moment; check landing CG.
- Ignoring datum sign conventions when arms are measured forward or aft.