Flight Performance and Planning
Mass and balance
Every load has a mass and an arm measured from the datum; moment = mass × arm. Total mass and total moment give the CG position. Check maximum take-off mass, maximum landing mass, maximum zero-fuel mass, and the forward and aft CG limits for the actual configuration.
Performance
Take-off and landing distances increase with mass, pressure altitude, temperature, tailwind, upslope and runway contamination. Density altitude is pressure altitude corrected for temperature; use it, not aerodrome elevation, when reading performance charts.
Fuel planning
Trip fuel plus contingency, alternate fuel, final reserve and any extra. Final reserve is typically 30 minutes holding at 1,500 ft for turbine aircraft and 45 minutes for piston aircraft under EASA-style rules; confirm the figure in your state's regulations.
Worked example
Empty mass 1,000 kg at arm 2.00 m; occupants 180 kg at 2.50 m; fuel 120 kg at 3.00 m. Moments: 2,000 + 450 + 360 = 2,810 kg·m. Mass 1,300 kg. CG = 2,810 ÷ 1,300 = 2.16 m. If the aft limit is 2.10 m the aircraft is out of balance even though it is below maximum take-off mass - the load must be redistributed or reduced.
Traps
Treating litres as kilograms (avgas is about 0.72 kg/L); omitting zero-fuel mass; ignoring wind on landing distance; rounding the CG before comparing it with the limits; using aerodrome elevation instead of pressure altitude for density altitude.