What is the standard lapse rate in the lower atmosphere?

• A. 0.5 inHg per 1,000 ft and 1 C per 1,000 ft
• B. 2 inHg per 1,000 ft and 3 C per 1,000 ft
• C. 3 inHg per 1,000 ft and 4 C per 1,000 ft
• D. 1 inHg per 1,000 ft and 2 C per 1,000 ft

Answer: (D)

In the lower atmosphere, the standard lapse rates used for aviation are fixed: pressure falls about 1 inHg for every 1,000 ft of altitude, and temperature drops about 2 °C for every 1,000 ft. This is the International Standard Atmosphere reference used to estimate how density, speed, and performance change with height. So, the standard combination is 1 inHg per 1,000 ft and 2 °C per 1,000 ft. That’s why the correct choice matches those rates. For example, at 5,000 ft, you’d expect roughly a 5 inHg drop from sea-level pressure and a 10 °C temperature decrease from standard sea-level temp.