Mass and Balance
Definitions
Know the terms: basic empty mass, dry operating mass, zero-fuel mass, take-off mass, landing mass, maximum structural masses, and the difference between maximum take-off mass (MTOM), maximum landing mass (MLM), and maximum zero-fuel mass (MZFM). Know that the mass of fuel is not part of the ZFM but is part of take-off and landing mass.
Moment and centre of gravity
Understand that CG position is found from total moment divided by total mass. Know the datum, arm, and moment, and the effect of loading on CG. Know the forward and aft CG limits and why they matter: forward CG increases stability and pitch-down tendency and can limit rotation; aft CG reduces stability and can cause pitch-up and stall recovery problems.
Loading calculations
Be able to compute take-off mass, landing mass, and CG from a load sheet. Know the difference between mass and weight (kg vs daN) and the conversion factor. Know the effect of fuel burn on CG: fuel in wing tanks moves CG little; fuel in fuselage tanks moves it more.
Traps
Questions confuse MZFM with MTOM, or forget to subtract trip fuel before checking landing mass. Another favourite: the effect of moving a mass on CG (ΔCG = mass moved × distance moved ÷ total mass).
Worked example
Aircraft mass 50,000 kg, CG at 25% MAC. Move 500 kg from a hold at 10 m forward of the datum to a hold at 20 m aft of the datum: the shift is 10 m aft, so ΔCG = 500 × 10 ÷ 50,000 = 0.1 m aft. The new CG is 25% MAC plus 0.1 m - check against the aft limit before dispatch.