The Bell 206 has a type of rotor system referred to as "non-rigid" -- the rotor hub is not fixed at 90° perpendicular to the shaft but rather can tip and swivel. Extreme pitch maneuvers, especially ones that induce negative G, can induce a phenomena known as mast bumping, where the hub assembly tips so extreme that it hits one side of the shaft.
The pilot had radioed just previously that he was immediately returning to base because of a fuel emergency. My guess is that he did an extreme push forward of the cyclic to pick up forward airspeed. This can induce a mast bump. A bad one can separate the hub from the shaft and we have a video still showing just that -- blades still attached to the hub but the whole assembly separated from the aircraft. I think the pilot triggered this.
Great insights, thank you.
Notice anything about the pilot?
I stand corrected and now put more credence on the original premise of a maintenance issue. Better pictures have emerged that show blades, rotor hub, shaft, and transmission gyrating through the air as an intact and separate unit. The blades look good, not mangled like they would be if they hit hit the tail empanage. There is some video showing of violent twisting action that probably broke it off.
This suggests that something seized violently in the transmission or engine -- transmission more likely because the sprag clutch would have let it free wheel if it had been the engine. That suggests a catastrophic mechanical failure. Could just happen, or could be the eventual outcome of poor maintenance. This will be interesting to follow.
I immediately wondered about pilot qualifications. Whether reacting with a bad choice to a fuel emergency or dodging a potential bird strike. But the emerging video shows this to have been sudden and violent. I retract my mast bump theory. Photo you provide also shows cyclic to be removed from left seat position (common in a tourist configuration) so it's not like the kid kicked the controls.
Once again, great insights. As somebody who spent a lot of time working in the aviation industry, i appreciate the more technical rationale.
