Heading discrepancy between PFD and map

[lalnaes]

On a recent flight, I noticed that the heading indicated on the Compass Rose / Directional Gyro on the PFD screen and the one on the Moving Map screen were quite different, in fact up to 17 degrees. At certain headings the PFD showed a lower heading figure than the map and at other headings the opposite was the case.

From which sources are the respective headings derived? Does the PFD use magnetic heading information from the ADAHRS and the map from the GPS-250? Can the discrepancy be caused by the ADAHRS not being in a magnetically benign location or poorly performed compass calibration?

Also, what is the source for altitude on the moving map. Is is the GPS-250 or barometric altimeter?

 

[dynonsupport]

Everything on the map page is GPS derived. The "heading" is ground track. The speed is ground speed, and the altitude is GPS altitude.

The PFD is all derived from the ADAHRS. It's standard indicated airspeed, pressure altitude, and magnetic heading.

So either wind or a poor compass location will cause a difference between the two heading readings.

 

[lalnaes]

Thanks for the clarification.