I have a Trutrack Digiflight IIVS getting its GPS input from a Garmin GNS430w. Recently, I have noticed approximately a 20 degree variation between the selected track dialed into the autopilot and the actual track that the aircraft flies. For example, today, I was directed by the controller to fly a heading of 70 degrees. When I dialed 70 degrees into the autopilot, the track displayed on my GRT EFIS, on the GNS430w and the autopilot itself showed 90 degrees. I had to dial in 50 degrees on the autopilot to get the aircraft to fly the 70 degree heading.
The variance is always 20 degrees more than I've dialed in. In other words, if I dial in a track of 60 degrees in the autopilot, the plane flies a track of 80 degrees.
This is a rather recent but consistent event.
When the autopilot is in the GPSS mode, if flies the correct track. In other words, if the waypoint that I have dialed in requires a 40 degree track, that is what the autopilot flies and is also what is displayed in the EFIS, the Garmin GNS430W and also the autopilot.
So, the autopilot always displays an actual track that agrees with the Garmin GNS430W and the GRT EFIS (which has its own built-in GPS), but whenever I dial in a manual track for the autopilot to fly, the actual track flown is approximately 20 degrees more than what I have dialed in.
I am thinking of recalibrating the magnetometer per the manual's instructions, but, my understanding is that the magnetometer is only involved when the autopilot is not receiving a GPS signal. When I manually dial in the track to be flown, my understanding is that the unit will use the GPS signal from the GARMIN GNS430w as its reference. Is this correct?
Or when I dial in a track manually, is the autopilot using its internal magnetic data as the reference? If this is the case, I can understand why I could get such a large difference between track dialed in and track flown, that is, if the unit is using its magnetic data.
Again, all of this assumes no wind.
Thanks,
Curt
The variance is always 20 degrees more than I've dialed in. In other words, if I dial in a track of 60 degrees in the autopilot, the plane flies a track of 80 degrees.
This is a rather recent but consistent event.
When the autopilot is in the GPSS mode, if flies the correct track. In other words, if the waypoint that I have dialed in requires a 40 degree track, that is what the autopilot flies and is also what is displayed in the EFIS, the Garmin GNS430W and also the autopilot.
So, the autopilot always displays an actual track that agrees with the Garmin GNS430W and the GRT EFIS (which has its own built-in GPS), but whenever I dial in a manual track for the autopilot to fly, the actual track flown is approximately 20 degrees more than what I have dialed in.
I am thinking of recalibrating the magnetometer per the manual's instructions, but, my understanding is that the magnetometer is only involved when the autopilot is not receiving a GPS signal. When I manually dial in the track to be flown, my understanding is that the unit will use the GPS signal from the GARMIN GNS430w as its reference. Is this correct?
Or when I dial in a track manually, is the autopilot using its internal magnetic data as the reference? If this is the case, I can understand why I could get such a large difference between track dialed in and track flown, that is, if the unit is using its magnetic data.
Again, all of this assumes no wind.
Thanks,
Curt