Aircraft Systems and Performance
What you must know
Candidates must connect systems knowledge to performance numbers. Understand the four-stroke cycle, the role of the mixture and carburetor heat, and how density altitude, weight, and wind alter takeoff and landing distances. Know the difference between indicated, calibrated, true, and ground speed, and how each appears on a POH chart. Learn the electrical system basics (alternator, battery, bus) and the pitot-static system's three instruments.
Traps
Density altitude is the classic trap: high, hot, and humid all reduce performance, and questions often give two of the three. Carburetor ice can form at temperatures well above freezing, especially with high humidity; do not assume warm means safe. Performance charts assume specific conditions (often no wind, sea level, standard temperature), so interpolate carefully and never extrapolate beyond chart limits. Distinguish best glide speed (engine failure) from best angle (Vx) and best rate (Vy).
Rule of thumb
For density altitude, remember the mnemonic "high, hot, humid = high DA = poor performance." A rough rule: density altitude rises about 120 ft per degree Celsius above standard at a given elevation.
Worked example
Field elevation 2,000 ft, temperature 30°C, altimeter 29.92. Standard temp at 2,000 ft is about 11°C. Difference = 19°C × 120 ≈ 2,280 ft. Density altitude ≈ 4,280 ft. Expect a longer takeoff roll and reduced climb; check the POH chart at that DA.