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Dynon D3 glitch

I was flying with an IR student yesterday in his own aircraft in hard IMC.

Spot the problem!

Power recycled…

Power recycled a second time

I believe the number in the centre of the Dynon (213 in the first photo) should be the ground track and match that on the Garmin GNS430 (287 – bottom middle of the six numbers).
The Garmin was correct while the Dynon indicated 90 degrees different.

I’m not familiar with the Dynon and perhaps it’s possible this could be configured to show heading rather than ground track, but if not I find it quite surprising that GPS ground track could be incorrectly calculated. I can only think that the unit might have been powered up just as we moved off blocks on the ground and immediately made a turn on to the taxiway.

I’m perplexed and interested in comments. It highlights the need to check compass/DI alignment, even with self-aligning displays of all types, and I confess I didn’t consider to check that instrument during the ground taxi checks. It’s an uncertified backup device intended for use only when the vacuum pump fails.

EGBJ, United Kingdom

Vibrations ? There are gyros and accelerometers in there feeding finely tuned filters and calculations. If it’s mounted at one spot and touching something else, like the top of the panel, that’s not good. Does it have a GPS, and/or electronic compass? (I think I remember the D5 to have only electronic compass ? ) If that’s the case, then it is very sensitive to vibrations, since the compass relies on accelerometers to work at all.

But then again, Dynaon … I have seen them fail. It could simply be it is faulty.


I am not sure what is the fail/refresh sequence on Dynon but on Garmin displays if magnetic sensor input is crap or fails*, the digital heading displayed on PFD will reverts to current/previous GPS ground tracks and you will see “no HDG flag”

*in theory, heading changes can be cross-checked vs pitot/static, turn rate sensor and acceleormeter while values against gps/magnetometer

ESSEX, United Kingdom

A couple of interesting things. First, on the third D3 photo there is no ‘Ext’ on the top left which means the D3 was using its own GPS built in aerial at this time. A duff external aerial then.

Secondly, there is no green battery power indication for internal battery on the third D3 photo It was taking power from an external power source as in the other D3 photos. See indicator at left of battery icon. This is strange as one would think there would be no reason then to deplete the internal battery.

This device cannot show heading, only track.

EGKA, United Kingdom

This device cannot show heading, only track.

Indeed. I know nothing about the D3 but no “GPS” can show the heading. The GNS underneath it cannot either. You need airdata input; basically an external AHRS with a fluxgate magnetometer.

And if not moving (as in the photo, I would assume) it cannot show track either. No GPS will show a track unless it is moving.

Shoreham EGKA, United Kingdom

All three pairs of photos show a fair ground speed displayed where the D3 matches matches the GNS 430 so I would say this ship was flying.

EGKA, United Kingdom

Yes, all three photos were taken in the air at around 4,000 feet with a groundspeed of around 120 knots. Each of the three was on a different heading/groundtrack.

Good spot on the External Antenna indication not being shown on the third photo – perhaps this was what was causing the problem. The battery indicator being empty on the third photo is a surprise, since it was taken only a minute or so after the second photo.

I did think the Dynon should be displaying GPS ground track and am still a little baffled about why it would display a track that is 90 degrees out rather than showing a fault/error. I don’t believe it would need any input from the AHRS to compute that. If there is an error, then I’d expect it to show a blank or error instead.

EGBJ, United Kingdom

I think that having the D3 on top of the panel gives it very good exposure GPSwise so I think the external aerial should be dispensed with for a trial. Also I suggest charging the internal battery before flight ( from a USB power pack maybe) and then using the internal batt of the D3 as the power source for the trial.

EGKA, United Kingdom
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