@ShyTorque
From the evidence already in the public domain, it appears that PB was flying a commonly used entry route to Battersea. He would have been directed to use that route because he would have been under radar control until he reported his position at, or in sight of, Vauxhall Bridge, a compulsory reporting point.
On reaching Vauxhall Bridge, he would have been required to turn almost 90 degrees right to fly westbound along the Thames, i.e. along helicopter route H4, to reach Battersea Heliport.
Thanks, quite possibly how the accident was instigated.