As the event progressed, temperatures hovered at -2 C, winds were once again calm, and the drizzle was completely liquid. This in-flight icing increases the drag on the aircraft which can adversely affect the flight performance. If the icing goes beyond the pneumatic boots, the aircraft performance may be compromised enough to cause trouble. There are three types of icing an aircraft may encounter in flight. Rime icing is rough, milky opaque ice formed by the instantaneous freezing of small supercooled water droplets.
Rime ice is brittle and tends to break off with pneumatic boots.
Clear icing is glossy, translucent ice formed by the relatively slow freezing of large supercooled droplets. This type of icing can be more hazardous as it forms a smooth, almost flexible, surface that does not easily break off. It is also more difficult to see and may not be detected by the pilot until it causes trouble. The third type, mixed icing, is a combination of riming and clear icing. Air parcels may be lifted by convection, terrain, fronts, smaller scale convergence boundaries, or larger scale cyclones.