Automatic Pilot Software

In many cases when you take a commercial flight, the plane pilots itself with the automatic pilot software. All the pilot does is take off and land the plane.

Typically when the plane has reached a certain height the pilot sets the automatic pilot.

This is the way the algorithm apparently works: the pilot sets the automatic pilot on a line going from A to B and the software maintains the plane on the line.

Anyone have first-hand information on this software?