Agreed there is no reason an EFIS can't pass heading information to an AP. But my TruTrak is not set up that way, and I'm not really sure if it can be; TT support told me the DigiFlight series cannot integrate in that way with the Dynon D-100 I have. Not sure if that is a design decision of TT for all EFIS, or just the D-100.drseti wrote:FWIW, both the Dynon D100 EFIS I have in my plane and the Dynon Skyviews I've flown in other people's planes have a magnetic heading indication available as a tape across the top of the screen. And, in both cases, the magnetic heading information comes from a flux gate magnetometer installed in the aircraft. The Dynon EFIS units work just fine with all GPS units turned off, and display magnetic heading, not ground track. So, if an autopilot is being driven by an EFIS, it should certainly be possible to select heading mode, to follow a magnetic pointing direction (properly known as a HEADING).
I can, however, understand why an AP manufacturer would want to rely on an internal magnetic heading source they have engineering control over, rather than a source from an external device where they have no control over the quality of the magnetic data. This both from a technical and a liability perspective; I would not want some other guy's device using my company's autopilot to steer a plane into a mountain because of a crappy compass.
