General
Precipitation can severely reduce Visibility (VIS) and can give a false optical illusion during the landing phase. A flooded, contaminated RWY may deteriorate the braking coefficient towards zero (aquaplaning).
Training reference only. Always defer to current approved manuals and official procedures.
Categories of Precipitation
- Vapor – Consists of very small drops of water which form haze, mist, and fog. This form of precipitation reduces the VIS drastically.
- Liquid – Forms of precipitation are drizzle and rain.
- Frozen – Forms are snow, snow grains, snow pellets, ice pellets, and hail.
Classification of Precipitation Intensity
With regard to precipitation, detection thresholds expressed in Millimeters per Hour (mm/h) are given for some sensors.
The World Meteorological Organization (WMO) reporting thresholds for light, moderate and heavy precipitation are shown in the table below:
Airframe Categories of Icing
- Rime – Thin milky film of frozen vapor.
- Frost – Rough, milky, and opaque ice formed by the instantaneous freezing of small water droplets or snow flurries.
- Clear ice – Glossy, clear, or translucent ice formed by slow freezing of water droplets.