For most of us, ice is a good thing. To pilots however, ice can be quite dangerous. Over a 10 year period, from 1990 to 2000, icing accounted for 12% of weather related accidents in aviation. So why is it so dangerous? Ice on the wings and other airfoils disrupts the air flow, decreasing lift and adding lots of drag. Tests have shown that ice on the wings of an airplane decrease the lift they can produce by 30% and add up to 40% more drag. Ultimately it can cause the aircraft to stop flying completely.
There are 4 different types of ice that form on aircraft. All have the same root way of forming. As an aircraft flies through clouds, it comes in contact with something called super cooled liquid water. Super cooled liquid water is water that is colder than freezing, but is still liquid. This happens because the water is so pure that it has nothing to freeze around. As the aircraft flies through it provides that something to freeze around. This is The first type of icing is rime ice. This type forms when smaller drops of water freeze quickly, creating a cloudy, rough texture. The next type is called clear (or glaze) ice. This ice typically happens at warmer temperatures, when the water does not freeze as quickly and haze time to spread out across the surface, making it clear and glossy. Sometimes, these two types of ice combine to give us the mixed icing. The final type of ice is the most common, frost. Frost forms on cold humid nights as the surface of the aircraft cools. Frost is also the most common.
Aircraft technology has allowed us to combat ice both before and during flight. Before flight aircraft are sprayed with both a de-ice and anti-ice fluid. The de-ice fluid removes ice that is already on the surface, while anti-ice prevents new ice from forming while taxiing and departing. Once in the air, some aircraft use systems to to prevent and remove ice. Jets, having the ability to use the hot exhaust from the engine, have heated edges to the wings and engines. These can be identified easily as they are chrome and shiny. Another way is to have a boot. This boot uses exhaust air as well to inflate and break off the ice. The last is called weeping wings. This uses a fluid that seeps from the wing to cover the surfaces and prevent the build up of ice.
So the next time you fly this winter, and your delayed while they spray, just remember its for a good cause.