直升機飛行員手冊直升機操作手冊 The Helicopter Pilot’s Handbook

時間：2011-04-05 11:37來源：藍(lán)天飛行翻譯 作者：航空 點擊：次

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The rate of accretion is important, not the characteristics of the icing, although clear ice is definitely worse than rime ice, since the latter contains air bubbles and is much lighter and slower to build—it also builds forward from the leading edge as opposed to spreading backwards. Variations on clear ice are freezing rain and freezing drizzle, both of which have larger droplets and are caused by rain, snow or ice crystals falling through a layer of warmer air at lower altitudes. However, the latter’s droplets have a much higher water content.
Although aircraft are different, expect icing to occur (in the engine intake, anyway) whenever the OAT is below 4°C. Otherwise, it can form in clear air when humidity is high— anti-icing should be switched on well in advance. Pitot head, static and fuel vent heaters should be on whenever you encounter icing, together with anything else appropriate.
You need warmer air to get rid of ice effectively – just flying in clear air can take hours. Climbing out is often not possible, due to performance or ATC considerations, and descending has problems, too – if you’re getting clear ice, it’s a fair bet that the air is warmer above you, since it may be freezing rain, which means an inversion, probably within 1000 feet or so, as you might get before a warm front. In this position, landing on your first attempt becomes more important as you are unlikely to survive a go-around without picking up more of the stuff.
Ground De-icing
Use either soft brushes, fluids, or a combination (try parking behind a friendly jet with its engines idling). Priorities are control surface hinges, engine intakes or static ports. Some manufacturers, however, don't recommend using fluids at all because of the possible effect on the bonding of composite materials. Warm water can be used, but I'm not so sure about that – I know if you want to freeze water quickly, you put it in the freezer hot.
De-icing Fluids
The main types are what used to be known as AEA (Association of European Airlines) Type I (unthickened) with a high glycol content and low viscosity, and Type II (thickened) with a minimum glycol content of about 80% which, with a thickening agent (one or two teaspoons of cornflour), remains on surfaces for longer, but remember it has to blow off before you actually get airborne. The idea is to decrease the freezing point of water but, as the ice melts, the fluid mixes with the water, both diluting it and making it more runny. What's left after repeated applications to combat this is of an unknown concentration, and may refreeze quickly. Type III lies somewhere between the two.
Type I fluids have good de-icing properties, but may refreeze—they are for de-icing, not anti-icing. Union Carbide Ultra fluid (potentially Type IV, and green in colour) appears to increase the times given by the tables below by 1.5 over Type II and way more for Type I – they give general guidance on the use of I and II, and the likely protection you might get on the ground (most fluids are gone by rotation speed):

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