FAA Part 107 Remote Pilot (UAG)WeatherMedium
The surface temperature at an sUAS launch site is 15°C. Using the standard atmospheric lapse rate and assuming no temperature inversion, what is the approximate outside air temperature at 5,000 feet MSL?
- A0°C
- B10°C
- C25°C
- D5°C
Show answer & explanationAnswer & explanation
Correct answer: D. 5°C
The standard lapse rate is approximately 2°C per 1,000 feet of altitude gain. At 5,000 feet, the temperature drop is 5 × 2°C = 10°C. Subtracting from the surface temperature: 15°C − 10°C = 5°C.
Why the other options are wrong
- A. 0°C would require a temperature drop of 15°C, which corresponds to about 7,500 feet, not 5,000 feet.
- B. This would be the total temperature drop, not the resulting temperature at altitude.
- C. This value incorrectly adds the lapse rate change instead of subtracting it.
Standard Lapse Rate
In the standard atmosphere, temperature decreases at a rate of approximately 2°C (3.5°F) per 1,000 feet of altitude gain.
- Standard sea-level temperature is 15°C (59°F)
- Standard sea-level pressure is 29.92 inHg
- Used to estimate temperature and density altitude changes with altitude
Memory trick: 'Two degrees, every thousand feet — like a countdown clock cooling the sky.'