FAA Part 107 Remote Pilot (UAG)WeatherHard
Surface temperature at a launch site is 12°C, standard lapse rate conditions apply, and no temperature inversions are present. At approximately what altitude AGL will the freezing level (0°C) be located?
- A4,500 feet
- B3,000 feet
- C6,000 feet
- D8,000 feet
Show answer & explanationAnswer & explanation
Correct answer: C. 6,000 feet
Using the standard lapse rate of 2°C per 1,000 feet, the temperature must drop 12°C to reach 0°C. Dividing 12°C by 2°C per 1,000 feet gives 6,000 feet, which is the approximate altitude of the freezing level.
Why the other options are wrong
- A. This value corresponds to only a 9°C drop, insufficient to reach the freezing point from 12°C.
- B. This would only account for a 6°C drop, not the full 12°C needed to reach freezing.
- D. This would represent a 16°C drop, overshooting the actual freezing level altitude.
Freezing Level
The altitude at which the outside air temperature reaches 0°C, calculated using surface temperature and the standard lapse rate, important for assessing structural icing risk.
- Standard lapse rate is 2°C per 1,000 feet
- Freezing level altitude = surface temp (°C) ÷ 2 × 1,000 feet
- Actual freezing level can vary due to inversions or moisture, so pilot reports and forecasts should be cross-checked
Memory trick: 'Divide by two, multiply by a thousand — count down degrees like steps up a ladder to the freezing floor.'