Flight Performance and Planning
What the exam tests
Flight Performance and Planning tests take-off and landing distance, density altitude, weight and balance, centre of gravity, fuel planning, and the use of POH tables and graphs.
Core rules
- Pressure altitude is indicated altitude with the altimeter set to 1013.25 hPa; density altitude is pressure altitude corrected for temperature.
- A useful rule of thumb: density altitude rises about 120 ft for each 1°C above ISA temperature at a given pressure altitude.
- Take-off and landing distances increase with density altitude; a rough planning factor is 10% more distance per 1,000 ft of density altitude.
- Weight and balance: moment = weight × arm; total moment divided by total weight gives the CG position. The CG must remain inside the forward and aft limits for all phases.
- Fuel planning must include taxi, trip, contingency, alternate, final reserve, and any additional fuel required by the operator.
Worked example
Field elevation 2,000 ft, QNH 1013, OAT 20°C. ISA temperature at 2,000 ft is 15 − (2 × 2) = 11°C. The temperature is 9°C above ISA, so density altitude ≈ 2,000 + (9 × 120) = 3,080 ft. If the POH sea-level take-off roll is 960 ft, add about 31% for 3,080 ft: 960 × 1.31 ≈ 1,258 ft. Use the chart value for the actual aircraft and conditions.
Traps
Do not use field elevation as pressure altitude when QNH differs from 1013. Do not ignore aft CG loading, which reduces stability and can reduce take-off performance. Do not plan with unusable fuel.