I was involved in the investigation of an R44 accident in a remote area. To cut a long story short, the pilot induced a loss of control and flew into terrain.
During the descent through trees, a substantial tree trunk caused the deformity of the pilot-side cabin and gave the pilot a good clout on the side of the head. Because he was wearing a helmet he was only stunned and not incapacitated.
It was thought that the same tree went on to pierce the pilot-side (auxiliary) fuel tank (not modified with the fuel bladder) which spilled contents on to the engine exhaust manifold.
When the pilot came round, he found himself unable to exit on the pilots side as the cabin had come to rest up against trees so he egressed out of the left side. He also found himself some way into the underseat baggage stowage as his seat had deformed into the crumple zone under the seat.
The aircraft was on fire so the pilot egressed with his survival go-pack which he had stowed on the back seat and although he made an attempt to douse the flames with the onboard fire extinguisher, the aircraft cabin burned to the ground.
What we learned
Wear a helmet - the pilot would not have survived if incapacitated
Fit bladder tanks
Dont fill up the underseat compartment as this is the crumple zone
Have your go-pack accessible
Know how to get out through alternative exits
The cause of the crash was not positively determined but low cloud and poor visibility were factors.