FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsEasy
A pilot is planning a departure from an airport at 3,000 feet field elevation on a hot summer afternoon. The pressure altitude is 3,000 feet, but the outside air temperature is well above the standard temperature for that altitude, resulting in a density altitude of 6,000 feet. What effect will this have on takeoff performance?
- AIncreased air density will shorten the takeoff roll and improve climb performance
- BDensity altitude will decrease, improving overall performance
- CThe higher density altitude will result in a longer takeoff roll and reduced climb performance
- DThere will be no effect because pressure altitude and density altitude are the same
Show answer & explanationAnswer & explanation
Correct answer: C. The higher density altitude will result in a longer takeoff roll and reduced climb performance
High density altitude means the air is less dense than standard, reducing engine power, propeller efficiency, and wing lift. This results in longer takeoff rolls, reduced climb rates, and reduced overall performance.
Why the other options are wrong
- A. Reversed — high density altitude decreases air density, not increases it.
- B. Incorrect — high temperature raises density altitude above pressure altitude.
- D. Incorrect — nonstandard temperature makes density altitude higher than pressure altitude.
Density Altitude
Pressure altitude corrected for nonstandard temperature; it represents the altitude the airplane 'feels' it is performing at.
- High temperature and high field elevation both increase density altitude
- High density altitude degrades engine power, prop efficiency, and lift
- Longer takeoff rolls and reduced climb rates result from high density altitude
Memory trick: Hot & high means less bite for your wings and prop