That was an engineering test gone bad. The aircraft is run from a control blockhouse, without crew aboard. The Chinook was tied down too tightly, so the landing gear oleos were not able to absorb the ground resonance motions effectively. This meant that on shutdown the ground resonance became severe, and the aft transmission failed in its mounts. Part of the problem is that the US Army does not believe in rotor brakes, so when this Chinook started experiencing the GR, the crew shut it down, but there was no way to quickly stop the rotor, so the aircraft was lost during the shutdown sequence, anyway. If there had been a rotor brake, putting it on would have caused all blades to the forward damper stops, which would have stopped the GR instantly (as well as slowing the rotor very quickly to help stop the freak show.)