Hi, I need some expert advice:

I had about 90 flights with my Mavic Air without any problem until last week.
I took off with all signals green and in GPS mode but instead of going up 1.2m and stabilising, the drone went immediately at an angle.
I never gained control. It went in different directions than my attempted commands and finally accelerated before crashing into a building.
Fortunately nothing was broken, nobody injured.
I recovered it with only one propeler and the two articulated feet broken.
When consulting the log, I noticed a few messages about altitude and IMU, and about interferences in the last seconds of the flight.
The drone seems to have reached 90km/h before crashing.
The log is here: https://www.phantomhelp.com/LogViewer/U823R1APPJVTQRUGBGJ7
I flew it again afterward, attached to a small wire, it seems to behave ok again.
What happened? How can I be sure it doesn't happen again?

interestingly, you had several IMU error messages and a few cell deviation prompts...your battery voltage appeared normal too.

possibly, your IMU was not calibrated and the interference caused by the reflection off the water waves - hmmm.

eug1388 Posted at 8-1 07:57
possibly, your IMU was not calibrated and the interference caused by the reflection off the water waves - hmmm.

Indeed, strange. No wind, no waves that day

eug1388 Posted at 8-1 07:55
interestingly, you had several IMU error messages and a few cell deviation prompts...your battery voltage appeared normal too.

What does “cell deviation” mean?

Thierry BKK Posted at 8-1 08:51
What does “cell deviation” mean?

I came across before the following (extracted from another thread).

Another way is upload your txt file in airdata website, which will offer you another flight log analysis, tks.

.....

Major deviation is when a cell differs more than 0.07v from the other cells, which normal batteries can have a few of these.

An abnormal battery will:
    A) Have most of the major deviations in one cell
    B) There will be multiple major deviations per minute, and more than 10 total
    C) The deviations continue longer than 1 minute

If your battery shows all symptoms (example, another) then this is considered a more severe case of an inefficient battery and may impact the battery life.
If your battery has only 1-4 instances on the same cell, don't worry too much about it. If it has 5-10 instances - then continue to track and make sure it does not degrade.

eug1388 Posted at 8-1 16:23
I came across before the following (extracted from another thread).

Another way is upload your txt file in airdata website, which will offer you another flight log analysis, tks.

Many thanks for your replies. I actually now uploaded more flight records on AirData and it's quite helpful to get more info out of these files. I now notice a lot of notifications such as "Not enough Force/ESC Error" or "Compass Error" including in the flights subsequent to the crash (the ones I had the drone on the leash to ensure it wouldn't fly away!). Although in these small flights the drone appeared to behave normally, it is still subject to many notifications. So I am going to seek further advice from DJI's after sales service but I suspect some repair / reinitialising will be required. Thanks again.

Thierry BKK Posted at 8-1 21:55
Many thanks for your replies. I actually now uploaded more flight records on AirData and it's quite helpful to get more info out of these files. I now notice a lot of notifications such as "Not enough Force/ESC Error" or "Compass Error" including in the flights subsequent to the crash (the ones I had the drone on the leash to ensure it wouldn't fly away!). Although in these small flights the drone appeared to behave normally, it is still subject to many notifications. So I am going to seek further advice from DJI's after sales service but I suspect some repair / reinitialising will be required. Thanks again.

First, Airdata shows less information that the Phantomhelp log viewer you already used.
2nd.  the minor battery cell deviations had nothing at all to do with the incident and are not significant.
They were probably more related to flying with a battery that wasn't fully charged than anything else.
A minor difference in cell voltages is common and doesn't cause a drone to take off and zip away at speed.

Your incident looks like it was due to a yaw error situation, probably caused by launching where you did.
Do you remember what direction the drone was pointing on the launch spot?
Was it west-northwest?   Or something else?

It acted normally on launching but picked up speed without corresponding joystick input at 0:08.4 when you turned the drone from the way it was facing for the launch.
What was the launch surface?
Was it reinforced concrete or was it close to some steel?

Labroides Posted at 8-1 23:20
First, Airdata shows less information that the Phantomhelp log viewer you already used.
2nd.  the minor battery cell deviations had nothing at all to do with the incident and are not significant.
They were probably more related to flying with a battery that wasn't fully charged than anything else.

Hi, thanks for your input. I launched the drone from a small wooden table placed on the beach and most likely I would have placed the camera facing the sea which was W-NW I think.

Thierry BKK Posted at 8-2 04:31
Hi, thanks for your input. I launched the drone from a small wooden table placed on the beach and most likely I would have placed the camera facing the sea which was W-NW I think.

I launched the drone from a small wooden table.
Steel bolts or screws in the table can cause the problem if they are close enough to the compass at power up time.

Hello there Thierry BKK. I am sorry for the trouble this has caused and thank you for reaching out. Kindly please try to calibrate the IMU of your DJI Mavic Air and can you please fly your DJI drone to a different location with less interference to see if the issue will still persist? The said DJI drone might have picked up magnetic interference on the ground, and you took off from close to a buildings with rebar concrete metal objects on it. Thank you.

DJI Stephen Posted at 8-2 21:23
Hello there Thierry BKK. I am sorry for the trouble this has caused and thank you for reaching out. Kindly please try to calibrate the IMU of your DJI Mavic Air and can you please fly your DJI drone to a different location with less interference to see if the issue will still persist? The said DJI drone might have picked up magnetic interference on the ground, and you took off from close to a buildings with rebar concrete metal objects on it. Thank you.

Thanks, I will do that re-calibration and follow it with some more "on the leash" flights to regain confidence before resuming normal operations!

Thierry BKK Posted at 8-2 22:33
Thanks, I will do that re-calibration and follow it with some more "on the leash" flights to regain confidence before resuming normal operations!

Hi there Thierry BKK. You are very much welcome and thank you for the reply. If you have any other concerns of inquiries with DJI. Please feel free to post it here at DJI Forum. Have a safe and a happy flying always.

Thierry BKK Posted at 8-2 04:31
Hi, thanks for your input. I launched the drone from a small wooden table placed on the beach and most likely I would have placed the camera facing the sea which was W-NW I think.

Possibly from one of wooden tables at Lollipop Cafe & Bar?
(If not, never mind.)


Appears to be two sizes.  Larger of two sizes appears to have two iron straps going across top.  Smaller tables don't appear to have metal straps.  But as Labroides points out, tables likely have ferrous metal bolts or screws, could even have iron corner brackets.

I had the same problem and all i did to fix it was to recalibrate the Controller

HedgeTrimmer Posted at 8-4 01:27
Possibly from one of wooden tables at Lollipop Cafe & Bar?
(If not, never mind.)

Indeed, small table

Rodney03 Posted at 8-5 01:06
I had the same problem and all i did to fix it was to recalibrate the Controller

Will do that then monitor the behaviour / flight records’ notifications and take it for repair if in doubt. Thanks