Outside air temperature

In aviation terminology, the outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft, but unaffected by the passage of the aircraft through it.

Aviation usage
The outside air temperature is used in many calculations pertaining to flight planning, some of them being takeoff performance, density altitude, cruise performance and go-around performance. In most texts, the abbreviation, "OAT" is used.

Units
Most performance and flight planning graphs and tables use either degrees Celsius or Fahrenheit or both. The Kelvin scale, however, is used for Mach number calculations. For example, the speed of sound in dry air is


 * $${c}= 38.945 \sqrt{K},$$

where:
 * $$c$$ is the speed of sound in knots,
 * $$K$$ is the outside air temperature in kelvins.