Oat, Sat, Tas??
 

OAT, SAT, TAS anybody could explain me the diferençes and when do u choose one owhen do i choose the other in a way that a could easily understand the diference???

OAT is measured at a ground location. During Taxi they ideally will all agree, although solar radiation may cause SAT & TAT to read high.

In flight at a significant Mach, you cannot measure SAT. You can only measure TAT (or a close approximation). SAT must be computed by the ADC.

SAT is Static Air Temperature, that is, the temperature of the 'free' air unaffected by your speed. OAT and SAT are essentially the same.

You didn't mention RAT or TAT, but you did mention TAS. Forward speed causes the air to compress as a function of Mach Number OR TAS, either may be used to calculate the Ram Air Temperature (RAT) / Total Air Temperature (TAT), or Indicated Outside Air Temperature (IOAT).

TAT = SAT X (1 + .2 X M^2), OR

TAT = SAT X (TAS / 87.1)^2,

Where TAS is in Knots, SAT and TAT are in Degrees Absolute, and M = Mach Number. The formulae may be reversed to convert TAT to SAT. (RAT differs from TAT by dint of the efficiency of the Temperature measuring probe).

OAT, SAT, RAT, and TAT are used in conjunction with Calibrated Airspeed (CAS) or Mach Number to calculate TAS. If CAS is used in the calculation, Pressure Height must also be known.

RAT/TAT usually determines the upper limit of the icing range of temperatures, OAT/SAT usually determines the lower limit.

Regards,

Old Smokey