@MBJ
it's not difficult to overload a Mi-8. Most of the russian ships carry at least one onboard (inside the cabin) additionally fuel tank (900 liters, also possible to carry 2 of these barrels). 20 passengers and their baggage, necessary survival equipment, urgent spare parts, tools, helicopter covers, grease, hydraulic fluid, short: all what you could find inside a russian helicopter... in 6600 ft is definitively on the upper point. In case of an engine failure and such an a/c weight it seems impossible to me to stay in the air and fly back home.
But ist seems also to me impossible that the crash is an overload problem. As every helicopter pilots knows you need the most power during take off and landing. And with a wheel gear it's easy to lift off and land with forward speed. That's also the recommended procedure in case of an engine failure or other emergencies. 70 miles flight distance means about 600 lbs of consumed fuel (depends from engine types). And it could be a modern type because of the voice recorder.
Could be a Controlled-Into-Terrain crash.