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Engine anti-ice
Hey guys
I'm a bit confused on the utilisation of the anti-ice as it's written on the FCOM: Engine anti-ice must be ON during all flight operations when icing conditions exist or are anticipated,ExCEPT during climb and cruise when the temperature is below -40 SAT.Engine anti-ice must be ON before and during descent in all icing conditions,including temperatures below -40 SAT. What's get me confused are the EXCEPT part of it and the below -40 SAT.the below -40 means (-39,-36 etc...) or (-41,-45 etc...)? |
-39 is warmer than -40, therefore below -40 means -41, -42, and so on.
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I'm surprised that question has even been asked!
Why not ask something slightly more relevant to the operation of the airplane with respect to engine anti-ice. A very simple question that you would be (again) surprised to find that some are not aware... Will the engine anti-ice system for an engine still work when the engine bleed air valve is closed? Does happen... EW73 |
Airbus defines icing conditions as "visible moisture".... less than OAT +10 until TAT -40.... blah blah blah..
here it is "Icing conditions may be expected when the OAT (on ground and for takeoff), or when the TAT (in flight) is at or below 10 °C, and there is visible moisture in the air (such as clouds, fog with low visibility of one mile or less, rain, snow, sleet, ice crystals) or standing water, slush, ice or snow is present on the taxiways or runways. |
Originally Posted by jimmyg
I am always amazed with the twits I fly with that think every cloud is icing conditions and ask for engine anti ice
Engine anti-ice must be ON during all flight operations when icing conditions exist or are anticipated, except during climb and cruise when the temperature is below -40°C SAT. Engine anti-ice must be ON before, and during descent in all icing conditions, including temperature below -40° SAT. When operating in areas of possible icing, activate engine anti-ice before entering icing conditions. WARNING: Do not rely on airframe visual icing cues before activating engine anti-ice. Use the temperature and visible moisture criteria because late activation of engine anti-ice may allow excessive ingestion of ice and result in engine damage or failure. |
Originally Posted by jimmyg
I am always amazed with the twits I fly with that think every cloud is icing conditions and ask for engine anti ice
Back in the good 'ole days, the BAe 146 icing definition was worse, and advice was that BAe would sue the next person who experienced an icing related engine roll back. :eek: |
Love the bun fight but I see nobody addressed the question.
The "except" part differentiates between thrust and idle where the intake pressure is very different. In the climb and cruise the intake temperature (T2) may well be equal or lower than SAT but during an idle descent the intake temperature could well be higher than SAT due to pressure effect. Thus the airframe may be operating below the magical -40°C but the intake temperature could be higher. |
One must also use good sense. The work that springs to mind is f@ckwit:ugh: |
My understanding is that flying in clouds=visible moisture so according to Boeing, as long as you are flying in clouds and TAT is equal to or above -40 degrees Celsius, engine anti ice must be ON which is exactly what I do. THe reason why the FCOM says it should be switched on during descent if TAT is below -40 is because temperature increases as you descend and if you remain in clouds, the TAT will eventually get into the "anti-ice on range"
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Old Thinking
Reminds me of the time during descent that I looked out the window as we started clipping the cloud tops and I could see the ice begin to build up on the inlet lip.
I asked the captain later if he had antiicing on and he said no, that he was aware of the possibility but thought he would wait and see if anything showed up on his engine instruments This was yesteryear thinking and hopefully not today's |
It's -40 SAT, not TAT. I'm hoping that you guys are looking at the right number in the plane, but not typing the right letter on the computer.
.http://images.ibsrv.net/ibsrv/res/sr...s/badteeth.gif |
Originally Posted by "Boeing 717 FCOM - Vol II Operating
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
SP.30.12 Cold Weather Operation (Continued) Engine anti-ice should be ON whenever icing conditions exist or are expected. Airfoil anti-ice should also be used if conditions warrant. Engine anti-ice should be used, and airfoil icing conditions can exist, when the TAT air temperature is less than 6°C (42°F) and there is visible moisture in the air. In addition to temperatures below 6°C (42°F), be alert for ice buildup on windshield wipers or edges of the windshields as indications of airfoil icing conditions. |
The warmer limit it TAT. It's above zero (7º or 10º) because the venturi effect at the intake lowers the temperature, perhaps cold enough to form ice.
The lower limit (-40ºC) is SAT, as water droplets in the environment at or below this temperature don't (theoretically) exist - there are ice crystals only. |
Imbracable Crunk
You are right. Guilty as charged. Typed the wrong thing but in reality, I check the FMC CDU for the SAT.
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Checkboard is right.
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So then it´s TAT+10 and SAT-40?
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OAT then TAT then SAT then TAT then OAT. Rat-ta-tat-tat.
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