DB - a double angle approach is also known as a steep approach i.e twice the angle as the normal site picture approach technique (taught to all pilots). To stay out of Vortex Ring territory you generally fly the approach a lot slower in the later stages to reduce the rate of decent.
Mister Bonkers, that's not the normal UK military's meaning of a "double angle approach". It actually means there are two angles of approach used, as outlined in Hughes 500's post. Although in my time as a QHI we taught pilots to set up a normal constant angle approach to the far side of the clearing, which amounts to the same thing as missing the near edge by 20 feet, I suppose. The second part of the "double angle" comes when there is tail clearance over the near edge and the aircraft can either go "forward and down" into the clearing, or completely vertical if necessary.
