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Cause of ATTI mode?

Joined
Jan 5, 2019
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#1
Hello everyone!

I'm new to flying drones but have over 300 hours of actual flight time in an ultralight.

I was flying my Mavic Pro Platinum on an overcast day, about 30 degrees out and with some snow on the ground. Winds about 12 - 15 mph. I had 18 satellites at the time that I took off.

I took off on a field and flew over a frozen river. I was at about 165 feet AGL (which as it turned out was too high to see the Mavic because of the low ceiling that day) when I saw a message about a compass error and it went into ATTI mode.

I dropped altitude until I was able to see it so that I could fly VFR. I then noticed that it was drifting in the wind and not holding position. I concluded the drifting was due to the loss of GPS in ATTI mode?

Once I lost altitude it recovered GPS and was no longer in ATTI mode.

I'm curious what might have caused the problem that put it into ATTI mode? Would the overcast sky have interfered with the GPS satellite reception?

From what I've read here, it sounds like the logs would tell the story. I deleted the logs a few days ago, however. So mainly I'm curious to hear what types of conditions you've seen where it will go into ATTI mode?

Thank you!
 

macoman

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#2
The logs will tell you exactly what happened but speculating, you bird likely suffered a strong interference that affected the compass.
 
Joined
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#3
Do you think the interference was due to the take off location? I was in an open field but I know there tends to be a lot of metal junk in the ground around here.
 

sar104

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May 27, 2017
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#5
If you saw a compass error then the reason for the switch to ATTI mode was a disagreement on the heading between the magnetometers (compass) and the rate gyros. When that happens the flight controller cannot trust that it knows the direction that the aircraft is facing, and therefore cannot hold position or navigate. It switches to ATTI mode in which all it does is hold the aircraft level and maintain altitude.
 
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