GRT Horizon EFIS HDG or TRK?

On a long flight today, I first noticed that the wind vectors (crosswind and headwind) were not adding up to the total wind velocity. This did not make sense to me but I did not notice anything else amiss. Then, I noticed that TRK was showing next to the compass/track heading box at the top just under the heading tape when HDG is usually displayed. This started me thinking that the reason the crosswind and headwind components were not adding up to the total wind velocity is because magnetic heading was missing from the calculation. I then pulled up the status setting of the EFIS and read the following error message: AHRS 1, Invalid Fine Magnetometer Calibration Data.

After a fuel stop, after the EFIS powered up, HDG was again displayed but as soon as I started taxiing, HDG changed to TRK.

Question 1. Does anyone think that the magnetometer needs re-calibrating per the manual? If so, why would it be needing this after operating correctly for over 200 hours?

Question 2. Does the HDG indication on the EFIS automatically default to TRK if the magnetometer is faulty and/or out of calibration?

Question 3. What determines weather HDG or TRK is displayed on the EFIS? If it is a user setting, why is mine switching between HDG (when I'm not moving or taxiing slowly) and TRK in the air?

As always, any thoughts would be appreciated.

Thanks,

Curt

First of all, wind components need to be added like vectors, e.g., a 10 knot headwind component and a 10 knot crosswind component means the total wind is 14.1 knots, not 20.
The GRT has an option in the setup, to show track or heading. If you select track, it probably defaults to heading when you are stationary (or moving very slowly) as it can't determine track if you aren't moving.
I do not know the answer to #2 but that is the way it's behaving.

It is too bad the pilot has to do all that debugging when the software should just say, dude, "I've got an issue". Been there, done that, published the youtube (slightly different issue).

Wow, really, the efis is showing a real 250kt cross wind? Trust, but verify.

Where is your magnetometer? If it's near the baggage area, did you put something back there that might be throwing it off? It's been known to happen.

How old is your AHRS? The newer ones (since just after the Mini came out in 2014) use GPS in addition to magnetometer data, so maybe if the magnetometer is being wonky, it's reverting to the GPS when you're moving because it's the more reliable data. This is all a guess- best call Mark at GRT to find out for sure.

The fact that the crosswind and headwind components don't add up to the total wind velocity is due to the trigonometry. It's not possible for them to do this unless one of them is zero and the other is 100% of the total wind (ie, angle of zero or 90 degrees).

So a 20 knot wind 60 degrees off the nose will produce a crosswind component of 17 knots and a headwind component of 10 knots (doesn't add up to 20).

A rule of thumb is:

Wind 30 degrees off the nose, crosswind = half the total wind strength exactly.

Wind 45 degrees off the nose, crosswind = 2/3 total wind strength (x0.7 if you want to be exact). Also if the wind is 45 degrees off, the crosswind and headwind components will be the same (as sin45 = cos45) but they still won't add up to the total wind strength.

Wind 60 degrees off the nose, crosswind = "almost all of it" (x0.86 to be exact).

Call GRT

There could be several possibilities with you track vs heading change. Every time I've had a question or problem GRT has ALWAYS been helpful in helping me discover what the problem was. One thing you probably want to do is do a flight data download and send it to GRT support with your questions. Good luck identifying the real causes of your problem.

PS. The builder of my RV did install the magnetometer for my airplane just below the rudder area net to my radio antenna. This did cause lots of heading issues and I eventually had to move it to the wing tip area as recommended by GRT. I mentioned this because a poorly placed magnetometer will cause significant heading deviation and it can be somewhat cumulative.

You can check the magnetometer calibration and accuracy in the setup page. If you do have an invalid calibration in one of your AHAR, it would be wise (and relatively easy) to recalibrate them. Like others said, there might be some interference that has cause the error but I doubt the interference will cause an invalid calibration instead of an error in the heading and then if that error is big enough will cause your AHAR to split (don't agree with one another)
As for HDG vs TRK, that is an option that is chosen in the setup page. The value in the box Initially it comes as a HDG and as soon as you establish a track (move to establish a track) it will show the TRK if that has been selected to show. I have two screens and I have setup my PFD to show TRK since that is a great help on ILS approaches and I do not need to account for wind correction as well as other situation and on my second screen which I typically show the map page, I have set it up to show the HDG in the box which typically air traffic controller's instructions are given to follow a HDG instead of Track. Both screens have option in the setup page to select how you like it displayed in the box. Please note that even if you select it to show as TRK, you still see the heading on the tape with the white color triangle.

I hope this has answered your questions.

KatieB said:

Where is your magnetometer? If it's near the baggage area, did you put something back there that might be throwing it off? It's been known to happen.

How old is your AHRS? The newer ones (since just after the Mini came out in 2014) use GPS in addition to magnetometer data, so maybe if the magnetometer is being wonky, it's reverting to the GPS when you're moving because it's the more reliable data. This is all a guess- best call Mark at GRT to find out for sure.

Click to expand...

Thanks Katie...I got the Same error message, but for both AHRS

"AHRS 1, Invalid Fine Magnetometer Calibration Data"