[TaMoDee]

I researched the weather data for the South Rim of the Canyon at the time of the incident.
Temp: 46F; Wind: West 9 mph Gusts 18 mph Sky: Clear

Normally not a problem for flying. BUT who knows what went on.

Helo’s have the glide path of a rock if the blades stop turning.

[JockoManning]

Small twisters can crop up suddenly, however. They are not that common in any one location but they do occur. I wonder if sudden isolated downdrafts can crop up similarly.

[steve86]

Helo’s have the glide path of a rock if the blades stop turning.

When has there been an instance of the blades stopping turning? If power was lost the blade pitch would be changed to autorotation configuration.

[Yosemitest]

Mechanical failure with gusting winds in a canyon is what I suspect.
Normally if the engine fails the blades will continue to rotate with the wind moving over them.
There's a procedure called "Auto-Rotation" that for emergency landings in such a situation with a pretty steep descent rate until enough speed for the rotors to slow the helicopter for landings obtained, but landing areas in the Grand Canyon are hard to come by, especially in the inner canyon.

Helicopters Won’t Just Drop Like A Rock If The Engine Dies ( 4:27 )


Autorotation - Landing a Helicopter without Engine Power ( 3:12 )