Performance
Performance
Performance examines take-off, landing, climb and cruise capability under real conditions: pressure altitude, temperature, wind, runway slope and surface. The exam expects you to correct chart values and recognise when a legal aircraft is operationally unsafe.
Core rules
- Density altitude: pressure altitude corrected for temperature. High, hot and humid conditions reduce air density and increase take-off and landing distances.
- Wind: a headwind shortens ground roll; a tailwind lengthens it sharply. Apply the chart’s wind correction, not the reported wind at a different height.
- Runway: grass, snow, slush, uphill slope and contaminated surfaces all increase distance. A wet runway may reduce braking action.
- Climb: aft CG, high density altitude and heavy weight reduce climb gradient. Obstacle clearance must be checked after the take-off distance.
- Landing: use the landing chart with the expected landing weight, not take-off weight, and add the prescribed factor for the runway condition.
Worked example
Pressure altitude is 4,000 ft and OAT is 25°C. ISA temperature at 4,000 ft is about 15 − (2 × 4) = 7°C, so the ISA deviation is +18°C. A quick density-altitude estimate is 4,000 + (120 × 18) = 6,160 ft. Enter the take-off chart at about 6,200 ft, not 4,000 ft, then apply wind and runway corrections. That may turn a comfortable runway into a marginal one.
Traps that cost marks
Using indicated altitude instead of pressure altitude, applying wind before temperature, and forgetting that a tailwind correction is not symmetrical with a headwind are frequent errors. Never use the take-off chart for landing.