At AMIL, many types of precipitation can be simulated under controlled environmental conditions. Several cold chambers are specifically designed for that purpose, as follows:
Freezing Drizzle (ZL)
Freezing drizzle is a fairly steady, light precipitation that forms a glaze-ice layer upon contact with the ground or the surface of an object. Its METAR code is FZDZ. The drop size of drizzle is smaller than that of rain, between 0.2 and 0.5 mm in diameter. Drizzle appears to float while following air currents, although, unlike fog, the droplets fall to the ground.
Light Freezing Rain (LZR)
Freezing rain occurs when supercooled liquid droplets freeze upon impact with cold surfaces, forming ice called glaze. The METAR code of Freezing rain is FZRA. The drop size of freezing rain is in the range of 1000 to 2000 μm.
Freezing Fog (FOG)
Freezing fog occurs when liquid fog droplets freeze to cold surfaces, forming white rime ice. It is a suspension of numerous minute water droplets in the air, at temperatures below 0°C, in the vicinity of the earth’s surface and affects visibility. Its METAR code is FZFG. Fog originates when the temperature and dew point of the air become identical, or nearly so. The drop size of fog is in the range of 20 μm.
Frost is the fuzzy layer of ice crystals on a cold object, such as a window or bridge, that forms by direct deposition of water vapor to solid ice. Frost occurs when water vapor deposits onto objects near the ground, the temperatures of which have fallen below the frost point due to radiational cooling overnight. It’s METAR code is FRST.
Natural snow crystals occur in a wide range of sizes, shapes, and water contents due to variations in temperatures and super saturations that snow crystals grow in. The process of snow generation, therefore, is difficult to reproduce in a cold room. The METAR code of snow is SNW.
In order to simulate the effect of natural snow on an aircraft de/anti-icing fluid, a snow simulation system was developed at AMIL. Ice particles are formed in a cold room and are distributed over a fluid-coated test plate by means of the snow distribution machine.
Artificial snow particles are made in a cold chamber by means of a pneumatic water spray nozzle supplied with water and compressed air. The laboratory-made snow particles are stored in an insulating container, which is placed in a freezer kept at a temperature below -10°C. The snow quality is verified prior to each test by means of a density measurement.
Ice Pellets (IP)
Ice pellets are small translucent balls of ice. They occur when raindrops freeze before hitting the ground or other surfaces. The METAR code of ice pellets is IP.