Mavic Air - Fell out of the sky - Weird error logged- Prop Failure???

Firejay27 · Apr 18, 2021

Well had my first crash with my Mavic Air (1st gen) and it totaled it. I had been moving around a building under construction from a very safe distance taking photos from various angles. This was my second time around. I had just hovered into position and let my fingers off the joysticks. Suddenly my live view goes crazy and within seconds I get a disconnected error.

Here's my flight log. From the log the aircraft appears to try and recover as it spiraled out of control. I looked up the error in the log and it seems commonly related to crashes immediately after receiving the error. No clue what caused it but the error in the log appears to come after the failure.

Took me a while to find it but because it maintained connection all the way to the ground the GPS pinpointed it exactly. When I did find it, I noted that 3 of the 4 props were broken however I couldn't find any pieces anywhere. Not sure where they went as this was all open ground dirt with no grass. From the ends though it appears that one or more of them failed with perfect straight snaps. All could have been broken on impact but something caused the failure.

I haven't had a single issue with my Air since I got it a few years ago and now I'm extremely disappointed as I was in the middle of a year long personal project. Anyone know a reliable source for a replacement Air? I would love to upgrade but I have 6 batteries, a DroneMax charger and all the Fly More combo accessories. Seems a waste to have to buy it all again and toss what I've got.

sar104 · Apr 18, 2021

That's a very unusual set of data. Looking at the vertical motion of the aircraft at the end of the flight shows an extremely high descent rate, peaking at 36.5 m/s (81 mph). That's well in excess of the terminal velocity of a falling Mavic, which is around half that value:

Even more strange are the attitude data, which indicate, as you alluded to, that after an initial unstable excursion, the pitch, roll and yaw were relatively constant and the aircraft was fairly stable:

None of that makes any sense to me. Can you try to recover the mobile device DAT file ending FLY041.DAT? That will contain a lot more relevant data.

Other than that - are those non-DJI props?

Firejay27 · Apr 19, 2021

The file is on my Android tablet thats charging. I'll pull the file tomorrow after work. Appreciate the feedback. From your initial analysis it sounds like the Air rolled over on its back and flew itself into the ground full speed.

And yes.. those are Mavic Air Screw props. I've been running them for a long time now. Never hit anything so there was no damage on them preflight.

sar104 · Apr 19, 2021

Firejay27 said:
The file is on my Android tablet thats charging. I'll pull the file tomorrow after work. Appreciate the feedback. From your initial analysis it sounds like the Air rolled over on its back and flew itself into the ground full speed.

And yes.. those are Mavic Air Screw props. I've been running them for a long time now. Never hit anything so there was no damage on them preflight.

Powered inverted flight would account for the descent rate, but the attitude data indicate that it was not inverted.

Firejay27 · Apr 19, 2021

Here's the .DAT file and the .TXT from my tablet. I noticed there were two .DAT files with FLY041 on them so I provided both.

Thanks for your assistance in figuring this one out!!

Firejay27 · Apr 19, 2021

Thought I would throw this in there for anyone following as well. Last moments from the .KML file and Google Earth. The weird ground is because I was flying over a construction site for which I had imported the blueprints for from the construction manager. Didn't get the angle of the screen snap very well but its a downward fall with the end of the line being where it hit on the ground. Looks like a bee going crazily round and round.

sar104 · Apr 19, 2021

Firejay27 said:
Here's the .DAT file and the .TXT from my tablet. I noticed there were two .DAT files with FLY041 on them so I provided both.

Thanks for your assistance in figuring this one out!!

I haven't seen that before. Firstly, the motor response, which is very strange in itself - at 486.8 seconds, all four motors spool up from around 10 krpm to over 14 krpm:

The two IMUs are in pretty good agreement on what happened; looking at accelerations, velocities and rate gyros:

If we believe those data, then the aircraft was facing 13° west of south and moving west at around 4 m/s when it appears to have been struck by something significant moving almost due north and downwards, knocking it backwards and pitching it forewards. Both IMUs recorded a rearward acceleration of around 7 g, and a rearward velocity excursion peaking at over 25 m/s. That would presumably have led to the broken props.

The event log indicates that the FC also detected an impact:

486.780 : 36400 [L-FDI][CTRL]: fault on , impact_in_air

486.800 : 36401 [L-RC]craft ctrl failed!!!

After that the aircraft seems to have flipped and then stabilized, but entered the rapid descent. I still can't account for the recorded descent speed, which seems to be confirmed by the IMUs VIO system and GPS data. However, the IMUs both report subsequent faults and so I would not rule out that the aircraft did, in fact, go inverted, and accelerate downwards:

486.846 : 36403 [L-FDI]NS(0) ACC(0): fault on , stuck

486.846 : 36403 [L-FDI]NS(0) ACC(1): fault on , stuck

486.848 : 36403 [L-FDI][IMU] gyro acc 0 err status 40c0

486.848 : 36403 [L-FDI][IMU] gyro acc 1 err status c0

Alternatively the IMUs and FC completely lost the plot, and the recorded telemetry is garbage, but the data are consistent enough that it seems unlikely. It does look like an impact in the air.

Firejay27 · Apr 19, 2021

Very very strange indeed. Appreciate your assistance greatly. While I didn't see any birds out it very well could have been a bird hitting it from behind. I have VLOS however and was using a daytime visible strobe as well which usually scares birds off. There was also a paragliding that was flying very low as well and I had to wait for him to clear the airspace and no birds were around then either. I didn't hear any gun shots so that eliminates being shot down. Grr... well its on its way to DJI so we shall see how much they want to charge me for non warranty repairs.

I'm super curious though why with no control input it went up first then down? Maybe a bird on the ground went up and knocked it from the bottom?

Who knows. Thanks again.

sar104 · Apr 19, 2021

Firejay27 said:
Very very strange indeed. Appreciate your assistance greatly. While I didn't see any birds out it very well could have been a bird hitting it from behind. I have VLOS however and was using a daytime visible strobe as well which usually scares birds off. There was also a paragliding that was flying very low as well and I had to wait for him to clear the airspace and no birds were around then either. I didn't hear any gun shots so that eliminates being shot down. Grr... well its on its way to DJI so we shall see how much they want to charge me for non warranty repairs.

I'm super curious though why with no control input it went up first then down? Maybe a bird on the ground went up and knocked it from the bottom?

Who knows. Thanks again.

You may have misread the graphs. Velocity is positive downwards, so it did not get hit from below - the impact was from above. And it was hit from the front and knocked backwards, not hit from the rear.