22 yrs Army helicopters, OH-58, TH-67 and later TH-57 experience. Taught the Maintenance Test Pilot course for Bell AH-1F Cobra. Mast bumping usually causes separation of the Main Rotor (M/R) hub from the mast. I does not usually pull the entire transmission out. The only thing that does that is excessive mast movement knocking the "candlestick" against it's stops under the XMSN. Watching the initial portion of the video, the aircraft appears to be flying level and cruising. I see no immediate maneuvers or disturbances until the severe yaw event that initiates the tail boom separation. My experiences point to 2 possible causes. The Tail Rotor (T/R) drive shaft hangar bearings on the 206 models (civilian versions of the 56, 57, and 58) are notoriously picky about accepting lubrication. They have been known to discolor and seize with little to no warning. Locking up the T/R drive shaft at the tail boom attach point bearing can cause separation, and the immediate torque due to loss of yaw control/tailboom could cause the whole upper pylon to become dislodged. The other option that comes to mind is pitch control link failure. I had a Cobra do that. When a P/C link fails, the M/R blades, or at least one, are no longer controlled and can easily flail themselves into the tailboom. That applies torque to the XMSN, potentially ripping it out. The fact the blades were still attached to the XMSN is what kept them rotating, like a toy set of blades on a stick. So, while I don't disagree that mast bumping could be a cause, the evidence I see doesn't lend itself to that.
Show less