De-Ice in vis Moisture

[Mtnjam]

Does anyone know when it is required or recommended to turn on De-Ice Equipment when you have Visible Moisture, meaning temperature's? I'm curious of the Highest and lowest Temps.

 

[Kaman]

Hello,

You'll hear a variety of "rules of thumb" for this, but +5C to -10C seems to be a pretty good place to start using your de-ice equipment.

 

[Lead Sled]

Does anyone know when it is required or recommended to turn on De-Ice Equipment when you have Visible Moisture, meaning temperature's? I'm curious of the Highest and lowest Temps.

It depends upon which equipment you're talking about. Certain "anti-ice" equipment is turned on, on the ground, prior to takeoff, rain or shine, day or night, summer or winter - pitot and static port heat and, in some aircraft, windshield heat (Strenghtens windshield for bird strike protection.)

Typically, you only use "de-icing" equipment - boots or TKS, as the need arrises. In the case of boots, there is usually a minimum temperature (-40C) below which you don't use the boots to avoid cracking them.

As far as "anti-ice" equipment operation goes, the AFM Limitations Section will usually contain the information. Typically at +5C or +10C when in visible moisture. The question then becomes - What constitutes visible moisture? Again, that is usally in the AFM as well and includes phrases like "visible moisture in any form" and "when visibility is less than one mile." As far as when can you safely turn it off - most every pilot will tell you a number (usually -30C to -40C). The arguement they give is that below "that" temperature, all of the moisture is already frozen and constitutes no danger, therefore the heat can safely be removed. Show me that in any flight manual. The worst icing that I ever picked up was at -38C.

'Sled

 

[Snoopy58]

Sled: the 737 flight manual says straight out that visible mositure & below +10 degrees C TAT, but above -40 degrees SAT, is icing. Colder than -40 SAT is NOT a threat. Engine anti-ice comes on at +10 TAT & colder (when in visible moisture), then off for climb & cruise at or below -40 SAT. Descending, it comes back on regardless of the temperature so you don't inadvertently descend into icing without the anti-ice on, but if you level off & it's still below -40, you can turn it back off.

Anybody who uses -30 instead of -40 is probably going to be in for some rude surprises!

 

[Lead Sled]

Show me that in any flight manual.

You showed me.

But my point remains, that it's information that's in the AFM. In the stuff that I've flown, there was/is no reference to a lower end.

'Sled

 

[Peanut gallery]

Anti-ice

All my manuals say +10 C TAT, and interestingly enough also reference low end by -40 C SAT. The question I have always had is why is one referenced to TAT and the other to SAT.
So, here you are flying in your jet, above 10,000 in the climb or descent, you are flying the speed of heat to get the ram rise above 10 C and you can leave the engine ice off. You climb higher and eventually have to turn the ice on, but if the SAT is below -40 C ( which depending on the airplane you may have to wipe out your wizz wheel to find SAT ) and magically you can now turn off the ice protection, because the logic is that at that temp moisture is next to neglegent due to saturation rates relative to temp. Is not ram rise changing the saturation rate relative to the actual temp and making higher moisture levels changing the logic? It just seems like a hole in the process.

 

[2000flyer]

Years ago, rule of thumb was turn it on +5 to -30°C. Later in life, mainly after Roselawn (ATR42), came +10 and colder. Personally, I have never picked up ice with temps in the -40°C range. Not to say it won't happen, I just haven't seen it.

Our manuals make no reference to -40. In the 2000, the limitation reads as follows:

"Icing conditions exist when the OAT on the ground and for takeoff, or TAT in flight, is +10°C or below and visible moisture in any form is present (such as clouds, fog with visibility of one mile or less, rain, snow, sleet, and ice crystals).

Now, technically, flying at FL430 with a TAT of -54°C through a high cirrus layer constitutes ice crystals. Again, I've never seen ice form on any surface in the above conditions.

2000Flyer

 

[ArcticFlier]

The only thing I have to add to the above is that we turn off the wing anti-ice above 230 kias in the CRJ, unless of course we get the 'ice' message on the EICAS.

AF

PS If you have an EMP gun, you can go with the anti-ice deferred.

 

[atrdriver]

In the ATR-72 we turn on prop heat and engine boots at 7 C TAT when in any visable moisture (atmospheric) and 5 C OAT on the ground. Pitot, static, and windshield heat are always on. We don't have a lower limit, probably because with a max altitude of 25000 we don't often have to worry about temps below -30...

 

[enigma]

Is not ram rise changing the saturation rate relative to the actual temp and making higher moisture levels changing the logic? It just seems like a hole in the process.

Dang good question. Also a question that illustrates the reasons why I'll never be a true genius, because I'd never even thought of it. Oh well.

enigma