Different headings on different instruments

[Mileage]

The attached photo was taken in straight and level flight over Eastern Long Island. Going from left to right, the headings displayed by various instruments are:

279 on the G5
278 on the GTX

255-ish on the magnetic compass
260 on the GTN650
260 on the mounted ipad using Foreflight

What might account for the 20-ish degree difference between the two sets?

 

[TCABM]

TRK ≠ HDG

 

[flyingron]

The G5 and GTX should read the same (a degree is probably just precision issues).
The GPSes don't have a clue about heading, only track. As TCABM points out, these differ based on winds, etc...

The compass may be thrown off by having the ipad next to it? Did you take into account the correction card? Are you accellerating/decellerating?

 

[Mileage]

Thank you. I've tried moving the ipad but it has no effect on the magnetic compass. The 20 degree difference with the magnetic compass is persistent in all conditions

 

[dmspilot]

Well 260 as displayed by your GTN and iPad is your track, not heading.

Did you take the average compass heading to account for oscillation error?

If you want to check the accuracy, it would be better to check it on the ground. Taxi down a long runway or parallel taxiway and compare it with the FAA published heading for that runway (not the runway number obviously, since it's rounded).

 

[Hang 4]

You are flying in a cross wind. Heading is where the plane is pointing, track is its path over the ground. Labels on the two matter. Compass should equal heading. For the compass, put your iPad on the seat and see if the compass changes. There's some strong magnets in a lot of iPads to hold covers and pens. Its pretty near the compass.

 

[mark.staggs]

Not sure about Cessnas, but Mooneys can get seriously magnetized from the steel frame and cause the magnetic compass inside on the glare shield to be quite a bit off from the slaved compass on the HSI.

Ditto the advice to check on the ground to see what might be causing it and what's accurate.

 

[Lindberg]

Is the 255 on the compass taking into consideration the deviation noted on the compass card?

 

[Mileage]

Is the 255 on the compass taking into consideration the deviation noted on the compass card?

I'm estimating the magnetic compass and the maximum deviation from the card is just a degree or two so I assume it's approximately 155. My real question is why it matches the GPS but not the magnetometer instruments in the first case. I have tried to move the ipad to see if it interferes - it does not. The attached pic is on the ground pointing down a runway with a published direction of 255 (PVC runway 25). The GTN reads 254, the magnetic compass reads about 230, the G5 and GTX read 236, so here the magnetic compass is clearly "off" but it does come much closer to the magnetometer instruments

 

[Bell206]

What might account for the 20-ish degree difference between the two sets?

I'd keep the mag compass out of the mix for now and work on the difference with the other avionics. Find you a certified compass rose and a helper to line you up or get you a certified master compass and go through the avionics calibration check again.

Once you determine those issue(s) then address the mag compass.

 

[Pinecone]

When was the last time the compass was swung and the correction card updated????

 

[TCABM]

I'm estimating the magnetic compass and the maximum deviation from the card is just a degree or two so I assume it's approximately 155. My real question is why it matches the GPS but not the magnetometer instruments in the first case. I have tried to move the ipad to see if it interferes - it does not. The attached pic is on the ground pointing down a runway with a published direction of 255 (PVC runway 25). The GTN reads 254, the magnetic compass reads about 230, the G5 and GTX read 236, so here the magnetic compass is clearly "off" but it does come much closer to the magnetometer instruments

Let’s look at systems to find some answers. The magnetic heading in the PFD and G5 is provided by a self-calibrating magnetometer that’s independent of the compass. That magnetometer should have been verified it was correctly configured after install with an ops check as part of the STC. The compass should have also been swung and a new correction card provided as a matter of good practice.

Since the PFD and the G5 appear to be getting data (no red X), the PFD amd G5system is getting data from the magnetometer; the question to answer is whether it’s correct or not.

Normally, you’d verify against the compass, but if you can’t verify the compass was swung during the avionics upgrade, you have no idea if it’s providing accurate information.

The TRK is a red herring; go look in the GTN documentation what the definition is for that field. Finally, the iPad and any associated cabling may be inducing interference. Test your setup with and without the ipad even in the plane. At a calibrated compass rose. That should give you an idea which, if any, of the magnetic heading devices is accurate or not.

 

[gacoon]

check this on the ground using a runway or taxiway with a known magnetic direction. during taxi Hdg and Trk should be real close. This should give you a good starting point to debug the situation.