Mass and Balance and Navigation Performance
Mass Limits
Maximum take-off mass, maximum landing mass, maximum zero-fuel mass and maximum taxi mass constrain the load. Basic empty mass plus traffic load plus fuel gives the take-off mass; the centre of gravity (CG) must lie within the forward and aft limits for the whole flight, including fuel burn-off.
CG and Performance
An aft CG reduces the elevator download needed, reducing trim drag and often increasing range and reducing fuel burn, but it reduces pitch stability. A forward CG increases stability but raises stall speed and drag. Mass affects take-off and landing distances, climb gradient, service ceiling and single-engine performance.
Balance Calculations
Moment = mass × arm. Total moment divided by total mass gives the CG position. Fuel burn moves the CG as fuel is used from tanks at various arms. Load sheets must be checked before departure and for landing.
Traps
Questions often ask whether the CG remains in limits after fuel burn, or how a load shift affects range and stability. Do not confuse mass limits with structural or runway limits.
Worked Example
Mass 2,000 kg at arm 2.0 m and 1,000 kg at arm 3.5 m: total moment = 4,000 + 3,500 = 7,500 kg·m; total mass 3,000 kg; CG = 2.50 m.