He wasn't intending to land. Sling cable would not release. Here is another view...
Telecom Tree Helicopter Crash - YouTube
Wrooster
So, he was lowering the cable down so someone could unhook it from the bottom of the chopper, and he clipped it?
I guess that makes sense. But, the tower is about as high as the cable is long; not a good plan.
This reminds me of the tow a boat with a helicopter video, same outcome. http://youtu.be/C4_13xYlgfY