Hi Everyone: I'd like to describe the "Pain in the S" turn to start.
The ideal turn is to follow the shape of a GS turn down the slope while using only short radius turns continuously along its path.
That being said, its purpose for the skier is to develop the movement skills, which will allow the skier to make turns which are similar in shape, flow, and rhythm, on an uphill side turn and a downhill side turn, while continuing on a curvilinear path across the slope, but not in a traverse, which is angular in nature.
However, it's very tricky because the uphill side turn requires a commitment from the CM to move up and over the top of the turn, kind of like a turn in the board park pipe on the up side, but without the skid or in a skier's case, without any hop up the hill. (This is what the examiner will look for.)
Next, as the skier moves toward the uphill turn he/she needs to roll from the current edge engagement of both skis as you move uphill toward the highside turn and then roll the skis toward the outside edges (those previously not engaged), at the peak of the turn, which puts the skis flat on the snow during the transition and then continue the rolling effort to the old outside edges, which causes the turn to speed up as you descend.
When the skier is moving toward the downside turn or bottom of the turn while transitioning, speed increases so the CM must be moved back across the skis sooner, so that the edge engagement occurs faster, but not harshly applied, to continue the same turn shape as the uphill side turn or a "J" turn will occur because of the rapid pressure build up at the turn bottom unless the skis are steered quickly back across with blended skills.
This is one of the difficult parts of this exercise.
Now all the while you are making these short radius turns, the side of the trail may be approaching, (here in the East at least), so typically most skiers find themselves too close the the trail's side to continue following the GS path smoothly and without making a sharp angular turn to change directions and stay on the GS path. So the trick is to make a slight direction change by moving your CM every second turn to face further toward the continuing path of the GS turn. This will allow small incremental direction changes, which will allow you to continue along the GS path.
The final trick is to start this entire exercise on a slight diagonal to the slope's fall-line, which will make the first major direction change somewhat easier, since the speed caused by the angle to the fall-line will be much less then if you were to try this down the fall-line.
I appreciate your patience with this lengthy explanation, but there is no easy way to describe in detail the nuances of this exercise. Good luck and have fun with it.
whtmt & Mackenzie 911