Last weekend I went out to take some pictures of skydivers (from the ground) using my D7000 and the Nikkor 18-200mm lens. Everything worked fine in all occasions except that the lens simply did not want to autofocus when set for AF-A with an "Auto" focus point.
It seems to me that this should be the ideal setup for a situation like this: I was trying to taking a picture of someone wearing a brightly-colored canopy (parachute) against a flat white sky. The lens would swing out to infinity, then back to minimum focus distance then give up. Needless to say, no shot. Just to see if it was the lens, I tried the same thing with a 50mm 1.8 and got the same results.
If I went to any of the other focus points, single or multiple, things worked much better. I read and re-read the "Understanding Nikon Autofocus" document and tried to find this on the forum but didn't come up with an answer. I'm hoping that someone can give me an idea what I may have either set wrong or expected wrong from my gear. Since I was never sure when the shot was going to present itself, or how far away my subject would be when it happened, I was hoping to hedge my bets by letting the camera do the heavy lifting.