Have you ever noticed that if you fly VOR radials based on the headings listed in a FSX flightplan, it doesn't quite match up with the flight plan course line on the GPS? Or that if you fly the headings listed on the flight plan, even when you are navigating by GPS you will go off course?
Turns out that, at least for the areas I've been flying, the courses listed between waypoints (VORs or intersections) are usually 2-5 degrees off from what they should be. I figured maybe it was just that the datum they used for the FSX map was different or something, so I tried a little experiment. I loaded my flight plan from KIAD to KCAK, which goes from AML -> TRIXY -> GRV. In the map view I put the plane on the GPS flight plan course line right over the "TRIXY" intersection, which (per the appropriate IFR enroute chart on Skyvector) is on the 300 radial "FROM" AML VOR. I went into the cockpit, tuned in AML, twisted the OBS and sure enough the needle was centered on 300. The flight plan listed the course from AML to TRIXY as 303.
I tried it again with the course from TRIXY to the GRV VOR...Skyvector listed the radial ("TO" GRV) as 310, which agreed with the VOR needle in the cockpit. The FSX flight plan listed that course as 315.
So, there's obviously a difference there that will impact you whether you are flying VOR radials or choosing your own courses to fly on a GPS flight plan (autopilot following GPS would not be affected). Does anybody know what gives? Has anybody found themselves right on the radial indicated in the flight plan but way off the GPS trackline because of this? Fortunately, Skyvector provides the right airway radial info for the US but my concern is once I start flying internationally!
Thanks -
Matt Smith - WWA2218
Washington DC (KIAD) Hub