Unstable magnetic heading

[spayne]

I noticed that my magnetic heading was very unstable today, and I was curious as to what might be causing it.

I have a D10A with a remote compass. On the ground things seem stable. In the air when I do a turn of more than about 90 degrees I can see the heading rate of change accelerate after about 90 degrees. The heading does not stabilize until about 5 seconds after the turn is complete. Even after small turns, there was several seconds of lag recognizing that the turn had begun and then another lag in heading stabilization. Also If I make pitch changes, the heading bar swings about 15 degrees. All of this was making it very hard to roll out on and maintain headings from ATC.

All of these things I would expect from a magnetic compass, but I thought the "gyro stabilization" would damp this out. Is this behavior normal, or should I start checking connections? I have seen this behavior before, but it seemed worse today.

I installed the most recent firmware when I was sent a replacement EFIS a couple of months ago. I verified that the compass has the same firmware as the EFIS.

 

[dynonsupport]

Does the heading eventually end up near-correct? If so, the "gyro stabilization", or the inertial aiding, might be off, which is to say that the EFIS itself needs a calibration here.

One thing you might try to start is a full heading recalibration, starting by verifying both the inclination and intensity numbers for your geographic location. The former should be between 50-70 in North America, the latter in the tens of thousands. A calibration with bad magnetic field values will give you some odd heading behaviors.

 

[spayne]

It does stabilize. I flew it again yesterday. It usually stabilizes after a 2 to 3 second lag. It is usually about 20 to 30 degrees behind the actual turn. On the ground it doesn't seem to have the same lag issue, it only happens when the plane is in flight.

I just performed a complete calibration on the unit when it was installed about 8 weeks ago. I will check the numbers again. When the calibration was done, it checked statically to within 2 degrees on all headings, but I did not do any sort of dynamic check.

 

[spayne]

I had used the horizontal field intensity rather than the total field number for field intensity. When I doubled the intensity number to its proper value and recalibrated, the instability problem was resolved.

Thank you!