Interesting flight path simulation to check out here. From an actual pilot.
https://youtu.be/XSHpbGhy3Ko
Still seems bizarre to me that the pilot would lose so much alt like this so quickly givin that he knew he was in mountainous area.. wouldn't he have remained high until he got some kind of visual of the terrain?
Do these helicopters not have auto pilot preplanned routes like airplanes? Seems like he should have had a path to travel on a map.
Going to agree with Oldman on this - he likely didn't realize that he was descending rapidly. People (even pilots) are used to using subconscious cues that tell them what is going on (leaning left, etc). These cues don't work when you are in an object moving in 3 dimensions, which is why accidentally flying into IMC (Instrument Meteorological Conditions, meaning you can't see the ground or horizon) kills people with alarming frequency. It takes some time to switch from looking outside to looking at your instruments and having your brain be able to process what you are looking at, and if you aren't trained in doing it, you are likely to crash anyways - there is a pilot training on this, titled "178 seconds to live," because pilots who are not instrument trained lose control and crash within 3 minutes on average in a simulator when losing outside visibility.
As for the route - while he may well have had a planned route, at the time he was operating under VFR and navigating by ground reference. He had been directed to follow the interstate, so he was flying a route that was not planned (vectors for traffic flow or weather avoidance are common in high traffic areas). Earlier in the flight he indicated that he was climbing to avoid a cloud layer. Again it is likely that he inadvertently lost sight of the horizon and became disoriented, likely without being aware of that fact. Unrecognized Spatial Disorientation is the most dangerous type of disorientation, since if you don't realize that you are disoriented, you aren't going to do anything to "re-orient" yourself, and are quite likely to slam your aircraft into the ground or otherwise put it into a dangerous state without realizing it. The sharp turn and descent are, as Oldman stated, a common result of such disorientation.
Mike
Edited to fix: The announcement that he was climbing to avoid clouds was several minutes before the crash, not immediately prior, as I originally posted. Still, inadvertent flight into IMC and resultant spacial disorientation is my candidate for most likely cause.