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dolin

Icing and Anti-Ice

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Hi, I have some doubts regarding the Anti-Ice system (both nacelle and wing)First: In the cruise section of every flight the Outside Air Temperature drops well below zero. Should I turn on the Anti-Ice? Is there a reasonable level of danger of icing, or at high altitudes and low temperatures (I normally cruise above FL350, and never below FL 300; I usually get temperatures below 20-25

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Icing can occur when there is liquid moisture below 10degrees C. (above ~10,000ft and below -10 it is not liquid so there is no need to worry too much).WAI is Wings Anti Ice, NAI is Nacelle Anti Ice (the bits around the engines.) Anti icing takes hot air from the engines, reducing the available thrust, which means longer take off runs or reduced payload capacity but also remember that in icing conditions the runway should be considered wet (or contaminated) which reduces breaking force and so means even longer runway is required for rejected takeoffs (or even lower payload capacity). When preparing for take off, consider anti-icing if the OAT is 10 or less and you can see moisture (Rain, snow, fog or low cloud). Before descending, consider anti-icing if you expect to encounter icing conditions during approach or landing. Icing builds up ice on leading edges which 1) changes their shape, 2) adds weight and 3) breaks off in chunks. All three are bad news as changed shape changes lift, extra weight needs more power and chunks falling off can jam and/or break things.

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Are there any differences of operation between NAI and WAI?
Ice build-up on wings seems to be slower on wings than nacelles, so WAI is generally used less often. On another forum, one real world 744 pilot claimed he had never used it. Note that WAI is not even active on the ground (airplane logic prevents it), but, of course, if you see ice/snow on the wings, then you should have the aircraft de-iced by ground crews before takeoff.Giulio, unless you have Auto Wing Anti-Ice, the use of WAI is usually determined by (pilot) visual sighting rather than by the temperature rule applied to NAI.Ice affects engines in two ways. If large chunks of it hit the fan blades, it can damage them. Also, if sufficient ice enters the core of the engine, it can cause a flameout. On aircraft with Rolls Royce engines, the ignitors are turned on (as a precaution) for a short period after NAI is turned on (depending on overhead ignition switch position).Hope this helps.Rgds.Q>

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My philosophy on ice equipment is it is there to get me out of icing, real world I never enter icing conditions on purpose.. but I'm not flying commercially (very often anyway).

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On aircraft with Rolls Royce engines, the ignitors are turned on (as a precaution) for a short period after NAI is turned on (depending on overhead ignition switch position).
Sorry, I should have said "automatically" ; )Rgds.Q>

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