"Can you explain the difference between loading and activating an approach in a GPS? I know this is a common area of confusion." - Joe M.
"We need to understand the difference between loading the approach and activating the approach, and what the GPS does in those circumstances.
If we've got a flight plan in, we know where we're going. We know we're going to such and such an airport, the ABC Airport. And perhaps there is only one approach and we have loaded that approach. Not a problem.
We still have a route to fly, though. We've got to go to the XYZ VOR, the RTS VOR, and then the ABC Airport, where we'll fly the approach. If we load the approach, great. That approach will be loaded in now at the bottom of the flight plan; as an amendment (so to speak) to the flight plan.
As soon as we activate the approach, the GPS is now going to navigate us to that first fix in the approach, and if we've selected Vectors-To-Final of the approach, it's going to navigate us in a straight line directly into the final fix and from there to the runway threshold.
Where I see people getting caught sometimes is activating prematurely, and the GPS now is no longer navigating along the route sequentially to the XYZ VOR, etcetera, but directly to that final fix. Or, perhaps to nowhere, save for a magenta line that is coming straight out from that final fix. If we've done that inadvertently, we need to know how to get back into the flight plan.
The other gotcha is that sometimes a final fix is also part of the route. However, the way we turn at that fix is determined by whether it's part of the route or part of the approach.
These are the little gotchas that GPS has."