FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesMedium
A pilot at an airport with a pressure altitude of 5,000 feet notes the outside air temperature is 30°C. Using the standard lapse rate of 2°C per 1,000 feet, what is the approximate density altitude?
- A8,000 feet
- B5,000 feet
- C9,500 feet
- D6,500 feet
Show answer & explanationAnswer & explanation
Correct answer: A. 8,000 feet
Standard temperature at 5,000 ft pressure altitude is 15°C − (2°C × 5) = 5°C. The actual temperature of 30°C is 25°C above standard. Using the rule of thumb of about 120 ft per °C deviation, 25°C × 120 ft = 3,000 ft added to pressure altitude, giving 5,000 + 3,000 = 8,000 ft density altitude.
Why the other options are wrong
- B. This is only the pressure altitude, ignoring the temperature deviation.
- C. This overestimates the correction beyond the actual temperature deviation.
- D. This underestimates the temperature deviation correction.
Density Altitude
Pressure altitude corrected for nonstandard temperature; it represents the altitude the aircraft 'feels' it is performing at.
- Higher temperature than standard increases density altitude
- Standard temperature decreases 2°C per 1,000 ft
- High density altitude degrades aircraft and engine performance
Memory trick: Hot and high means density altitude flies sky-high