The bank is a condition of tilted wings, and the turn is the change in the direction which results. The connection between the two is inexorable: The airplane must bank to turn, and when it is banked it must turn...The miraculous part of the maneuver is that the turn has an important balancing effect on the bank that causes it. The same effect, in cruder form, steadies cars on banked roadways, and bobsleds on the vertical walls of icy tracks. The difference in airplanes is that as the bank angle increases, the turn also quickens and by doing so automatically delivers a balance that is perfect. Bicycles react similarly: When they start to topple, they turn and thereby keep themselves up. Airplanes are even steadier. They operate in three-dimensional space and do not rely on tires to keep from sliding to the side They will never capsize no matter how steeply they are banked.