TAT probe indication - A320
 

During icing conditions the probe heat is selected when on the ground. The TAT probe is not heated in this case, so, my question is, how accurate is the SAT on the ground? I mean, if the ATIS is indicating zero degrees, but the SAT shows 2 or 3 degrees (after several hours sitting at the bay), is it ok to use what is indicated on this system?

Many thanks.

Better to use the temp given by ATC on the ground.

SAT and TAT probes are designed to operate when the aiplane is moving through air.

So when sitting still on the ground, they are not accurate and are usually off by 2-4 degrees celsius.

So on the ground, the only temp you SHOULD rely on is what is given to you on the ATIS or by the tower...

Its as simple as that!

FCOM
 

FCOM is specific about this and says not to use SAT indications on the ground but to rely on reported temperatures.