FAA Aircraft Dispatcher (ADX)Flight Planning and PerformanceEasy
A dispatcher notes that surface temperature at the departure airport is significantly higher than standard for the field elevation. All other factors being equal, how will this affect the airplane's required takeoff distance?
- AIt will decrease because engine power output increases in warmer air
- BIt will increase because higher density altitude reduces engine and aerodynamic performance
- CIt will decrease because warmer air reduces aerodynamic drag on the airframe
- DIt will remain unchanged since takeoff distance is based only on pressure altitude
Show answer & explanationAnswer & explanation
Correct answer: B. It will increase because higher density altitude reduces engine and aerodynamic performance
Higher-than-standard temperature increases density altitude, which reduces air density, engine thrust output, and wing/propeller efficiency—all of which increase the required takeoff distance.
Why the other options are wrong
- A. Warmer air decreases air density, reducing engine power output, not increasing it.
- C. Warmer air does not meaningfully reduce aerodynamic drag; the dominant effect is reduced air density.
- D. Takeoff distance depends on density altitude, which includes temperature, not pressure altitude alone.
Density Altitude Effect on Takeoff
Higher density altitude (from high temperature, high elevation, or low pressure) reduces air density, decreasing engine power, propeller/wing efficiency, and increasing takeoff distance.
- Density altitude = pressure altitude corrected for nonstandard temperature
- High density altitude reduces engine thrust and lift
- Takeoff distance increases as density altitude increases
Memory trick: 'Hot and high, harder to fly.'