Flight Performance and Planning
Performance, mass and balance, fuel
Performance questions ask you to apply data, not memorise it. Know the definitions of take-off and landing distances (ground roll versus to 50 ft), the factors affecting them - mass, density altitude, wind, slope, surface condition - and how each factor moves the numbers. Density altitude is the key concept: high temperature, high elevation and low pressure all reduce air density and degrade both engine and wing performance.
Mass and balance: understand maximum take-off and landing mass, zero-fuel mass, and the centre-of-gravity envelope. Forward CG increases stability but raises stall speed and stick forces; aft CG reduces stability and can make recovery from a stall difficult. Compute CG by summing moments (mass × arm) and dividing by total mass.
Fuel planning: know trip fuel, contingency, alternate and final reserve, and the difference between taxi fuel and reserve. Traps include using pressure altitude instead of density altitude, forgetting to correct for wind when computing ground roll versus air distance, and mixing units (litres versus kilograms versus pounds).
Worked example
Aircraft mass 1,000 kg at arm 2.0 m; add 100 kg at arm 3.0 m. Moments: 2,000 + 300 = 2,300 kg·m; total mass 1,100 kg; new CG = 2,300 / 1,100 ≈ 2.09 m. Check this against the envelope - a small aft shift can still be legal, but only the envelope decides.