Difficult to make much out from the photo but I'd suggest that the problem might lie with a fractured prop attach flange on the crankshaft rather than the propeller itself. As a matter of general interest, there are six attachment studs holding the prop hub onto the flange (either secured with 3/4" AF self-locking or wirelocked nuts, I forget which). There's no way they would come undone.
A close-up photo would give more clues.
Last edited by stevef; 8th July 2009 at 11:30.