SOLUTION: Earth has a radius of 6371 kilometers. A pilot is flying at a steady altitude of 5.6 kilometers above the earth's surface.
What is the pilot's distance to the horizon?
The pilot's distance to the horizon is a leg of the right angled triangle, whose hypotenuse is (6371+6) = 6377 kilometers,
and the other leg is exactly the Earth radius of 6371 kilometers.
So, the answer is = 276.5 kilometers.