Pilots don’t rely on a single metric to determine the temperature of the air outside of an airplane. Most cockpits display several different air temperatures, including total air temperature (TAT), static air temperature (SAT) and International Standard Atmospheric (ISA) temperature
What Is TAT?
TAT represents the temperature of the air outside of the airplane. More specifically, it’s calculated by taking the SAT and adding the temperature increase associated with flight. As airplanes fly, they will heat up. TAT takes into account this temperature increase. It’s the SAT plus the temperature increase associated with flight.
What Is SAT?
SAT is the ambient temperature of the air outside of the airplane. Also known as outside air temperature, it’s influenced heavily by the altitude at which an airplane flies. The higher an airplane flies, the lower its SAT — as well as its TAT — will be. At 30,000 feet, most airplanes have an SAT of about minus 40 to minus 50 degrees Fahrenheit. SAT doesn’t take into account the temperature increase associated with the flight; it simply represents the ambient temperature and nothing more.
What Is ISA?
Finally, there’s ISA. ISA temperatures are those calculated using the ICAO Standard Atmosphere. It’s used for comparisons against the atmosphere. Pilots can compare the actual atmosphere to that of the ISA.
Differences Between TAT, SAT and ISA
TAT, SAT and ISA aren’t the same. Many airplanes feature cockpits that show all three of these temperature-related metrics, but there are nuances between TAT, SAT and ISA.
SAT is one of the most common temperature-related metrics used by pilots. On the exterior of a typical airplane is a temperature-sensing probe. This probe will constantly measure the ambient temperature while subsequently relaying this information to the cockpit. SAT is a measurement of the temperature sensed by this probe.
TAT is a similar temperature-related metric used by pilots. It’s essentially the same as SAT but with an added factor: the temperature increased associated with flight. It’s calculated by taking the SAT and adding the flight’s temperature increase to it.
ISA is probably the most unique temperature-related metric of the bunch. It involves the comparison of the atmosphere to a universal, standard atmosphere set by the ISA. The ISA has benchmarks for air pressure, density and temperature.
In Conclusion
There’s not a single temperature that pilots look at when flying. Rather, most pilots analyze several different temperature-related metrics, including TAT, SAT and ISA.
