I was talking to a person on a bus while I was in Washington DC recently. He was from Florida, and he was talking about the storms they’ve been having this winter. He said he completely understood why airplanes couldn’t fly with ice on their wings and tails; it’s because the ice is so heavy that it pulls the plane down.
He was rather surprised to learn that he was wrong.
The weight of the ice can be a problem, especially if you are talking about ice picked up in flight. The main problem, though, and the reason a visual check of the wing may not be enough to keep you out of trouble for your preflight check, is that ice on the wings spoils the airflow. Even bits of ice as small as grains of salt can decrease lift and increase drag. If you’ve planned a flight based on the normal flight capabilities, ice on the wings can cause you to run out of fuel, for instance, or stall at a speed and attitude that is usually safe. Another issue, if you are talking about bigger pieces of ice, is that a piece of ice can come off the wing and hit some other part of the airplane.
The lift generated by the wing is dependent on the shape of the wing. Even tiny changes in the shape can change the airflow. If the air coming off separates from the wing too soon, you don’t get the lift you need. Ice can also form on propellers, limiting the efficiency and increasing the work required from the engine. Some planes have boots on the leading edge of the wings that can be inflated so the ice breaks off. There are also several other options, including bleeding heat off of jets to keep the wings warm enough so they don’t ice up (which I think is really neat).
Checking for ice before you fly is a good start. There is another problem, though, that you need to keep in mind. Moisture in the air can be supercooled. This means that the water can actually be below freezing, but because there is nothing for the water to freeze around, it stays in a liquid state. If you introduce something new, such as the wing of an airplane, the water immediately crystallizes into ice. A pilot flies into a cloud with no ice on the wings and suddenly has a noticeable accumulation of ice. Not a good thing. If you fly VFR (visual flight rules – no cloud flying!) this part of wing icing shouldn’t be an issue, but if you are flying IFR (instrument flight rules) and it’s cold outside, this can cause you pretty serious issues. You can still get wing ice if it’s cold and you aren’t flying through clouds, but it isn’t quite as dramatic.
Wing icing is not something you want to take chances on. If it’s cold out, run your hand over the flight surfaces when you are doing your preflight. You’ll feel ice if it’s there, and you’d rather find out before you take off than realize there’s an issue when you can’t make the turn out of the pattern.