# How can OAT and SAT differ?

I always thought SAT (Static Air Temperature) and OAT (Outside Air Temperature) were the same thing. So does this answer, so does Wikipedia:

[The] outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft.

So, what is the difference based on that video capture?

• @mins if you want something even more confusing, check my answer below :D – ymb1 Sep 24 '16 at 4:20
• Ah, yes now I'm lost and frightened. @Daniel's answer contains a table for COAT (SAT) that corresponds to the more conventional idea (and the difference is smaller). Also this seems interesting: Temperature Measuring Instruments – mins Sep 24 '16 at 4:43

From the manual:

So it appears that this instrument's terminology is a little non-standard.

From the Youtube video, you can see that they are moving at a fair pace:

If you take these numbers and plug it into the equations from this question,

$$Ram~Rise=SAT\times0.2\times{M}^2$$

(remembering that SAT needs to be in degrees Kelvin)

You come up with

$$Ram~Rise=(273-33)\times0.2\times{0.491}^2 \approx 11.6C_{rise}$$

Which is pretty close to what you see in the video.

Here is the conversion chart of OAT to SAT in the POH for that (or similar) airplane.

No other qualification is given, but my assumption is that OAT is not TAT, and would be wrong to label it that... it is just the raw temperature sensor value.

• The chart you provided shows no more than 1°C difference. Yet the picture in the question shows a difference of 10°C. What gives? – TomMcW Sep 24 '16 at 19:10

The manufacturer (Shadin) apparently uses unconventional OEM terminology:

Air Temperature (OAT/TAT): The outside air temperature (OAT, also known as total air temperature) is the reading from the aircraft’s outside air temperature probe. The DigiData provides static air temperature (TAT, or true air temperature) at speeds above 20 knots. Due to the friction between the air and the outside temperature probe, the temperature rise must be subtracted from the OAT. This correction yields the TAT, sometimes called static air temperature (SAT).—Shadin

So their TAT can be True or Total. Both of which the opposite of what we know.

• Except now "TAT" means "true air temperature" not "total air temperature"? lol – Daniel Sep 24 '16 at 4:14
• Oh man, what's with these people using non-standard terminology? So a pilot sees OAT of -20°C expecting it is corrected for ram rise (which in most aircraft it is). He looks up in his handy chart and makes the proper 710ft altitude correction. Little does he know that the actual/static/true air temp is - 30°C and requires a 950ft adjustment. Let's just hope he has at least a 240ft margin of error to get over that mountain – TomMcW Sep 24 '16 at 19:18