World Magnetic Model introduction
You’ve set yourself up for a challenge and plan for a VOR approach. At the final approach fix, you turn inbound and perfectly center the CDI on the final approach course of 85 degrees. As you get closer to the runway you notice the CDI drifting. As you are trying to get back on course you notice that you need to fly 87 degrees magnetic to keep the CDI centered. An already challenging approach is getting more complicated.
This scenario is all too common in most simulators. The problems are caused by outdated magnetic variation data. In short, magnetic variation is the difference between where the true north pole is and where your magnetic compass says it is. Traditionally, simulators like Prepar3d contain maps that provide this information. However, magnetic variation changes each year and the maps are often old. While you fly your updated charts during the approach, the simulator is applying old outdated information and leading you off course. Solutions are to regularly update the magnetic variation data, but the updated packages are still static low precision snapshots that become outdated.
The solution is the World Magnetic Model. Instead of looking up data, modern Flight Management Systems calculate the currently active variation based on a database of variation and drift rates. This leads to highly accurate data that does not get stale. Starting this year, ProSim based simulators will use this model instead of relying on the underlying simulation platform to provide magnetic variation. This will ensure that your up to date charts can be flown exactly like in real aircraft.