Ok, when you turn on final you're lining up with the ILS (unless you're doing a visual) and that guides you straight in. But when I've watched planes land, sometimes they will kind of "zig-zag" on final. They'll go to the left of the runway, then execute another turn back, go a little to the right, then turn again. I saw it a couple months ago at HSV - an Atlas 747 heavy was approaching. Must have been at least 10 miles out. But it kept turning till maybe 4 or 5 miles then lined up straight with the runway. There was no other traffic. Why do they do that?
I've only seen it from the ground. I don't ever recall it happening when I was on a plane - all the approaches seem like they line up and go straight in for 7 - 10 miles.