Performance
What the exam tests
Performance tests take-off/landing distance, climb gradient, obstacle clearance, density altitude, V-speeds and limitations. Iran's high aerodromes and summer temperatures make density altitude a recurring theme.
Core rules
- Density altitude = pressure altitude + 120 ft per °C above ISA (approximation).
- Take-off distance increases with altitude, temperature, weight, tailwind and runway slope/contamination.
- Climb gradient % = (height gained / horizontal distance) × 100; rate of climb = gradient × ground speed.
- V1, VR, V2 change with weight, altitude and temperature; use the approved chart.
- Contaminated runway: use contaminated factors; do not use dry figures.
Worked example
Aerodrome elevation 4,000 ft, QNH 1013, OAT 35°C. ISA at 4,000 ft = 15 − 2×4 = 7°C. Deviation = 28°C. Density altitude ≈ 4,000 + 28×120 = 7,360 ft. The take-off chart must be entered at 7,360 ft, not 4,000 ft. Reasoning: high density altitude reduces thrust and lift; using pressure altitude alone underestimates the distance.
Traps
Using QNH elevation instead of pressure altitude; forgetting the temperature correction; using TAS instead of ground speed for climb rate; applying dry runway data on a wet runway; ignoring obstacle gradient after engine failure.