TAT or SAT

[SkyPigPilot]

I thought I understood this issue. Now I am completely confused. Thanks Guys.

 

[h25b]

Splitting hairs???

In the Lear 35 with a SAT of -56°C (ISA) doing Mach 0.78 your TAT would be about -30°C, that is a 24°C difference (43.2°F difference) TAT vs. SAT...

I would hardly call that "Splitting Hairs"...

O.K., the splitting hairs remark was a poor choice of words to say the least along with the guy that said this discussion wasn't interesting...

Now excuse my ignorance and educate me please. When defining "icing conditions" in terms of temps. at which ice accumulation occurs do the manufacturers (i.e. Learjet, Dassault, Raytheon, etc...) vary on which temp. to use ???

Now, if the true ambient temp. (i.e. SAT) is not conducive to ice accretion but the TAT is .... THEN WHAT ?? I guess my question comes from the point that I have evidently ignorantly been going by SAT and have never been surpised by ice forming unexpectantly.

If the SAT is so cold that icing is virtually impossible is it then possible for the ram-air heating effect to somehow create an a condition where icing is possible... ???...

 

[FlyChicaga]

Actually, you use both SAT and TAT for ice protection purposes.

On the EMB-145, we will use SAT temperature with visible moisture for determining whether or not to use engine anti-ice for takeoff. 10 degrees C SAT is the limit. However in flight, we use TAT to determine the need for ice. Actually, since our system is automatic, the airplane determines for itself when it needs ice protection. However, for our ice protection system checks, we must be below 10 degrees C TAT.

So the above posts are right; TAT is used in flight to determine the need for anti-ice. However, SAT is also used, but on the ground.

 

[LarryinTN]

TAT=SAT when you're airspeed is zero.

 

[Dog Driver]

oooops

 

[beytzim]

I see this all the time! Too many pilots who have no idea how to read a TAT/SAT gauge.

TAT is what the airplane feels it is outside. So you better turn all your anti-ice equipment if its below +10TAT. Some manufacturers have limits on the minimum temperature to put anti-ice on. I've seen -27TAT, -40SAT etc. Regardless, the vast majority of icing will occur between -10TAT and +10TAT in visible moisture.

Example: You are doing 250KIAS at 10,000. Your TAT gauge reads +8 and SAT is -12. Better put that anti-ice on. Your smart Captain brings the throttles up and accelerates to 330IAS. Guess what? SAT is still -12, but TAT increased to +13. Turn off the anti-ice, you don't need it anymore. Know the relationship between IAS and TAT and you'll be a much safer pilot.

Happy flying.

 

[FurloughedAgain]

I think the confusion arises because some aircraft (specifically the light lears) specify SAT.

I don't understand why either, but perhaps there's an engineer type out there who can explain it to us.

This is the first airplane i've flown where TAT is ignored -- sometimes much to our detriment while trying to climb with the anticlimb selected "on".

 

[bestpilot]

I'd kinda be thinkin....What if I was like a itty bitty like molecule of like air, and like I'm just chillin' and mindin my business, y'know, and like hangin with dem other oxygen and nitrogen dudes, and all da sudden,

WHAM!!!!!!! Smacked by like dis big wing and stufff! OUCH!!!!

Yeah, I guess I'd be gettin heated up about dat, so is dat kinda why like TAT is like hotter dan SAT????????

Freakin wierd, Dude, yeah, wierd.

 

[TooBad]

I'll go with Albie on this one