FAA Private Pilot Airplane (PAR)Weather Theory and ServicesHard
A pilot departs an airport at a field elevation of 2,000 feet MSL where the surface temperature is 20°C. Assuming a standard atmosphere and standard lapse rate, what outside air temperature should the pilot expect upon reaching 8,000 feet MSL?
- A8°C
- B4°C
- C14°C
- D12°C
Show answer & explanationAnswer & explanation
Correct answer: A. 8°C
The standard atmospheric lapse rate is approximately 2°C per 1,000 feet of altitude gain. Climbing from 2,000 feet to 8,000 feet is a gain of 6,000 feet, which produces a temperature decrease of 6 × 2°C = 12°C. Subtracting this from the surface temperature: 20°C − 12°C = 8°C.
Why the other options are wrong
- B. 4°C would result from an incorrect lapse rate calculation using too many degrees per 1,000 feet.
- C. 14°C results from using only a 3,000-foot altitude gain instead of the correct 6,000 feet.
- D. 12°C is the amount of temperature decrease, not the resulting temperature at altitude.
Standard Lapse Rate
The standard atmospheric temperature lapse rate is approximately 2°C (3.5°F) per 1,000 feet of altitude increase, used to estimate temperature aloft under standard conditions.
- Standard lapse rate: 2°C per 1,000 ft (or 3.5°F per 1,000 ft)
- Standard sea-level temperature is 15°C
- Used to estimate freezing level and temperature at altitude
Memory trick: 2 degrees Celsius cooler for every thousand feet higher