Aircraft Performance and Weight and Balance
What the exam tests
Performance questions test takeoff and landing distance, obstacle clearance, climb gradients, density altitude, contaminated runway effects, and weight-and-balance limits. You do not fly the aircraft, but you must decide whether the planned weight, runway, and conditions make the flight legal.
Core concepts
- Pressure altitude is indicated altitude with the altimeter set to 1013.25 hPa; density altitude is pressure altitude corrected for temperature.
- High elevation, high temperature, and high humidity increase density altitude and degrade takeoff, climb, and landing performance.
- Takeoff performance must satisfy field length, climb, obstacle, and brake-energy requirements. Landing performance must satisfy landing distance and missed-approach climb.
- Contaminated runways increase stopping distance and reduce friction; use the approved contaminated-runway data.
- Weight and balance must remain within MTOW, MLW, MZFW, and the CG envelope throughout the flight as fuel burns.
Worked example
Airport elevation 4,000 ft, QNH 1013, temperature +30 C. Pressure altitude is about 4,000 ft; ISA temperature at that altitude is about +7 C, so the day is ISA +23. Density altitude rises well above 4,000 ft, perhaps 8,000 ft equivalent. The dispatcher must use the high-density-altitude takeoff chart, not the sea-level chart, and may need to reduce payload or fuel to meet the obstacle and climb limits.
Traps
Using airport elevation as pressure altitude; ignoring temperature correction; using dry-runway data for a wet or contaminated runway; checking takeoff weight but not landing weight; and assuming CG stays fixed as fuel burns. Always use the aircraft-specific approved data.