My flying buddy, while hovering his Trex 450SA yesterday about 2 feet off the ground, had the rotor head come apart like a deer getting hit by a semi. Both main blades separated at the grips; the grips actually fractured at the "ears", the ears and blade pivot bolt stayed attached to the blades as they flew over 40 feet from the main crash site. As the heli now has no means of lift or cyclic control, it smacked hard into the ground at full power and tipped over, thus destroying what was left of the head. This all happened in a matter of one to two seconds. All that remains useful are the mixing arms, linkages and the aluminum head block. Probable cause I found to be overtightening of the main blades causing an overstress on the main blade grips, then adding in a headspeed in the neighborhood of 2700 rpm gives an immense load on the main blade grips (I'm still trying to calculate that force, I'll post it later with pics).
The main point of this is to watch the tension on the main blade grips. But more importantly, has anyone ever heard of this happening before?