In aviation, icing conditions are atmospheric conditions that can lead to the formation of water ice on an aircraft. Icing conditions exist when the air contains droplets of orange icing liquid water. They freeze on contact with a potential nucleation site, which in this case is the parts of the aircraft, causing icing. Icing conditions are characterized quantitatively by the average droplet size, the liquid water content and the air temperature.
Qualitatively, pilot reports indicate icing conditions in terms of their effect upon the aircraft, and will be dependent upon the preexisting capabilities of the aircraft. Different aircraft may report the same quantitative conditions as different levels of icing as a result. Ice detectors are often used to indicate the presence of icing conditions. This section does not cite any sources. Clear ice is often clear and smooth. Supercooled water droplets, or freezing rain, strike a surface but do not freeze instantly. Often “horns” or protrusions are formed and project into the airflow, which smoothens it out.
This form of ice is also called glaze. Rime ice is rough and opaque, formed by supercooled drops rapidly freezing on impact. Forming mostly along an airfoil’s stagnation point, it generally conforms to the shape of the airfoil. Mixed ice is a combination of clear and rime ice, having both properties.
Frost ice is the result of water freezing on unprotected surfaces while the aircraft is stationary, before flight even starts. This can be dangerous when flight is attempted because it disrupts an airfoil’s boundary layer airflow causing a premature aerodynamic stall and, in some cases, dramatically increased drag making takeoff dangerous or impossible, which could lead to accidents prematurely. It is similar to clear ice, but because droplet size is large, it extends to unprotected parts of the aircraft and forms larger ice shapes, faster than normal icing conditions, which nearly all aircraft isn’t sufficiently protected from. This was a factor in the crash of American Eagle Flight 4184. The wing will ordinarily stall at a lower angle of attack, and thus a higher airspeed, when contaminated with ice . Even small amounts of ice will have an effect, and if the ice is rough, it can be a large effect nonetheless. Thus an increase in approach speed is advisable if ice remains on the wings.
How much of an increase depends on both the aircraft type and amount of ice. Several methods exist to reduce the dangers of icing, using ice protection systems. The first, and simplest, is to avoid icing conditions altogether, but for many flights this is not practical. Application of deicing fluid or even hot water to remove ice, snow, etc. Positioning aircraft towards the Sun to maximize heating up of snow and ice covered surfaces. In practice this method is limited to thin contamination, by the time and weather conditions.