Flight Performance and Planning
Flight Performance and Planning tests whether you can turn POH data, mass and balance and fuel figures into a safe go/no-go decision. Namibian high-ground airfields make density altitude a favourite.
Density altitude
Pressure altitude is indicated altitude with 1013 hPa set. ISA temperature at elevation is 15°C minus 2°C per 1,000 ft. Density altitude ≈ pressure altitude + 120 ft per °C above ISA. It raises take-off distance, reduces climb rate and increases TAS for a given IAS.
Mass and balance
Moment = mass × arm. Total moment divided by total mass gives CG. The CG must stay inside the envelope from empty through zero fuel to landing; aft CG reduces static stability and can make stall recovery harder.
Take-off and landing data
Use the POH chart for the actual pressure altitude, temperature, wind, slope and surface. Interpolate; do not use the sea-level column. A wet grass strip can add a large distance penalty.
Worked example
Field elevation 5,500 ft, QNH 1013 hPa, so pressure altitude 5,500 ft. OAT 30°C. ISA at 5,500 ft = 15 − (2 × 5.5) = 4°C. ISA deviation = 26°C. Density altitude ≈ 5,500 + (120 × 26) = 8,620 ft. Use the 8,600 ft chart line, not 5,500 ft.
Traps
Using elevation as pressure altitude when QNH is not 1013; mixing °F and °C; ignoring wind/gust; using the dry runway chart on wet grass; forgetting that aft CG is not automatically 'better performance'.