This situation is prone to icing. Low level This type of cumulus congestus may hide
stratus and other grey clouds may have a severe intermittent icing.
high water content.

Although the grey clouds contain This type of thick stratus looking like heavy
supercooled liquid water, the situation is soup with a mountain blockage, may be a
too windy to be a big icing threat except threat for icing.
inside the cumulonimbus.

Figure A1

A1.3 Ice shapes accreted in flight
In-flight icing experience shows a very large variety of ice accretion shapes and textures. Some are flat, some look like lace, some are like a hedgehog or a sea urchin. Others are single or double bumps, running along the leading edge, surprisingly pointing forward. But it is a hopeless task to try and relate the shapes with a given flying condition.
There is a very large number of parameters which may influence the icing process. A non-limiting list can be:
●
Air temperature: OAT or  SAT

●
Aircraft speed or total air temperature: TAT

●
Aircraft size

●
Type of cloud

●
Type of precipitation

●
Liquid water content of the air mass

●
Liquid water drop size distribution (see: certification)

●
Possible presence of ice crystals

●
Total water content of the air mass

●
Aircraft skin local temperature and heat capacity

●
Type and extent of the de-icing or anti-icing system.

The individual influence of each parameter noted above present a very difficult theoretical problem. The various influences are not at all additive. Shapes can range from a pure moon arc adhering on the leading edge, to a double horn (a nightmare for the aerodynamicist), or a flat, grooved plate, downstream of the leading edge itself (which is called runback ice), or even .shark teeth., pointing towards the airflow and randomly distributed aft of the leading edge. Moon arc is generally made of pure ice (called black ice or clear ice, as both mean the same!); double horn is often made of white, rough ice, called rime ice. At temperatures around 0 °C, rime ice is full of air bubbles and/or water flowing through.
The innumerable variety of ice shapes, particularly of those made of rime ice, reveals how complex the ice accretion process may be. Due to historical and technical reasons, a fully comprehensive study is virtually impossible.
For example, in reviewing the influence of flying speed: Speed has an effect on several characteristics of the ice which accretes. The best known effect is kinetic heating (KH). Kinetic heating is the difference between TAT and SAT. For example, at 250 kt, KH is about + 10°C. Those 10° show in a temperature increase of the leading edge relative to the rest of the airframe. KH is sometimes called temperature recovery, because it naturally heats the leading edge and therefore somewhat protects it from icing, as long as the outside air is above - 10°C.
　
中國航空網 www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：getting to grips with COLD WEATHER OPERATIONS 寒冷天氣運行(17)