Last night on a routine flight something strange happened. The phantom had been flying for about 7 minutes and still had plenty of battery. I was not in a hurry and was bringing it back home. All of a sudden, the phantom started tumbling and angled down (almost vertical) and hit the road. I was about 20 feet from where it went down. Remarkably, there was a crack in the case and a bowed area. I was nowhere near the CSC or cutoff position on the controls. Here is the strange part. One of the propellers was missing. It didn't bounce away from the crash site. I am sure the crash was caused by a propeller departing. I do not tighten the propellers. (I have the spin down type.) Am I making a mistake? The phantom started up with all four motors running. Amazing.