Outside air temperature (OAT) is defined as which of the following?

• A. The measured or indicated air temperature corrected for compression and friction heating; also referred to as true air temperature.
• B. The measured temperature at altitude.
• C. Ambient temperature uncorrected outside the aircraft.
• D. Dew point.

Answer: (B)

Outside air temperature is the ambient temperature of the air in the atmosphere outside the airplane at your current altitude, as measured by the outside air temperature sensor. That’s why the best description is the measured temperature at altitude. It represents the actual environmental air temperature, not the air after it has been heated by the aircraft’s motion. The other phrasing describes true or total air temperature, which includes ram/heating effects and is higher than ambient, while dew point is a separate property of moisture in the air.