Jim,Andrew,
Boeing made a very convincing argument for a rotor in the wake of United 585 but the NTSB was never fully convinced and said that while a rotor may have struck the aircraft, triggering the deployment of the rudder, the fact that the latter jammed was the cause the crash, not the rotor. I'm no expert but from what I've read the NTSB claimed that the intensity of rotor likely to have been around that day would have been insufficient to twist a large jet transport out of the sky (eyewitnesses are reported to have seen it twist on its back, then dive stright into the ground)especially as nothing appeared to have broken off the plane in the air.