This probably happens more than you would think. I was online at the NTSB site looking for info on the Hendric Motor Sport crash and looked up the list in the month, and saw two crashes in the town I used to live in in Ohio. As I read each one I saw that it was two planes but one crash. The same thing happened there. They were doing "hit the numbers" and the 152 was long, and did a touch and go. He cut his pattern short and when he lined up again a 172 was over top of him coming in and didn't see the 152 under him till they touched. They spiraled down from about 400 ft and the one on the bottom received pretty serious injuries when the plane caught fire. My mom used to work for the guy in his restraunt back in the 50's. Thing is the runway comes right up to my sisters farm, converted to a golf course. Normaly they land from north to south but that day the wind had them landing from south to north. Had it been the other way around, they would have crashed on the back nine! My brother-in-law wouldn't have been happy about that I can tell you! Course it wouldn't have been the first time. I guy died in a crash in his melon field one year.