I've read the "Saving a flight" part of the introduction manual and it doesn't contain any particularly useful information pertaining to my problem. It just says "Saving a flight is done via the P3D Flights/Save menu and will save the airplane position, status and configuration into a file that can be loaded at a later time via the P3D Flights/Load menu."
Yes I was using the plane before trying to load the save. Like I said in my post, I had just landed at Rotterdam. I also tried closing down the game and loading the save straight from the scenario editor and got the same thing.