Lost mavic air

Geokok · Aug 12, 2019

Last week I was flying my mavic air and while I was flying it back I lost connection and the drone. I tried to look for it, the area is difficult to access and to walk on it, so I had no results until now.

I based my search on the scenario of a sudden shut down, and we searched around the last reported point.

Could you please have a look on the flight log and suggest the behaviour of the drone after the loss of connection? The battery was at 17%, was at a RTH process?

Also could you suggest a search area?

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I appreciate your support on this!!!

Regards,
George

Skywalker · Aug 12, 2019

I thought there was a safety in that if you lost connection and didn’t recover within parameters a MA would RTH on its own? I’ve had a couple panic moments where I lost transmission and hit RTH, wondering if I since lost transmission how would it receive to command. But it always comes home...so far. I suppose issues here could be fighting wind on a 17% battery causing a forced landing, or not being high enough and catching some foliage?

Deleted member 94047 · Aug 12, 2019

Geokok said:
Last week I was flying my mavic air and while I was flying it back I lost connection and the drone. I tried to look for it, the area is difficult to access and to walk on it, so I had no results until now.

I based my search on the scenario of a sudden shut down, and we searched around the last reported point.

Could you please have a look on the flight log and suggest the behaviour of the drone after the loss of connection? The battery was at 17%, was at a RTH process?

Also could you suggest a search area?

DJI Flight Log Viewer | Phantom Help

Upload and view DJI Phantom, Mavic, and Spark flight logs online

www.phantomhelp.com

I appreciate your support on this!!!

Regards,
George

Sorry to hear about your misfortune. That doesn't look too good. Your best bet is to upload the .DAT file associated with that particular flight and have some one like @sar104 have a look. You will find the DAT file in the DJI>dji.go.v4>FlightRecord>MCDatFlightRecords folder of your phone/tablet if you are using android.

Meta4 · Aug 12, 2019

Geokok said:
I based my search on the scenario of a sudden shut down, and we searched around the last reported point.
Could you please have a look on the flight log and suggest the behaviour of the drone after the loss of connection? The battery was at 17%, was at a RTH process?

Unless you changed the Loss of Signal action in the app (you didn't) the drone will attempt to RTH on loss of signal.
The programmed behaviour on loss of signal is described on page 14 of the manual:
When Failsafe RTH is activated the aircraft starts to retrace its original flight route home. If the wireless control signal is re-established within 60 seconds of Failsafe RTH being activated, the aircraft hovers at its present location for 10 seconds and waits for pilot commands.

On loss of signal the drone would have retraced its track until reconnecting.
If reconnection did not happen, the drone would have flown straight toward the home point.
There were no obstacles on the RTH path to block the return and the altitude was well clear of the ground.
But .... the drone was already down to 17% battery.
From 30% until the end of data, the drone was flying approximately toward the home point in sport mode.
The right joystick was pushed full forward but speed was only 4.8 metres/second, indicating a stiff headwind to fight against going home.

The drone is unlikely to have made it all the way home at the slower speed that RTH uses and probably burnt battery trying, eventually reaching critical low battery level and autolanding .... maybe in the water or perhaps somewhere on the part of the RTH path over land.
@sar104 is the guy to calculate/estimate when the battery might have run down to autolanding level.

There's approximately 400 metres of the approx return path over land and 260 metres over water.

Geokok · Aug 12, 2019

Doppler said:
Sorry to hear about your misfortune. That doesn't look too good. Your best bet is to upload the .DAT file associated with that particular flight and have some one like @sar104 have a look. You will find the DAT file in the DJI>dji.go.v4>FlightRecord>MCDatFlightRecords folder of your phone/tablet if you are using android.

Thank you all for your concern!

I attach the .dat file.

Geokok · Aug 12, 2019

the dat file

Geokok · Aug 12, 2019

Geokok said:
the dat file

@sar104 will you be able to have a look at this log? Thank you!

George

Meta4 · Aug 12, 2019

Geokok said:
@sar104 will you be able to have a look at this log? Thank you!

There's probably not much additional information in the .dat file that would be of much use in this instance.

sar104 · Aug 12, 2019

This is a little complicated. Firstly, due to the high wind speed out of the north (~ 12.5 m/s @ 348°), the aircraft would not have made it back to the home point:

The flight log ends at 616 seconds, but the battery level would have fallen to the autoland level 20 seconds after that, at 636 seconds.

The question, of course, is what happened. There are no precursor indications of signal loss, and the aircraft had line of sight to the home point when the log stopped. The obvious causes are sudden power loss on the aircraft or the app crashed. The less likely cause, since the connection had been fine, is actual loss of downlink to the RC.

If it were sudden power loss then the result is obvious - the aircraft falls out of the sky. With the high wind speed and light mass of the MA it will actually have been blown some distance from the last recorded point:

That looks like this on Google Earth:

That puts impact 35 meters SE of the last recorded point.

If the app crashed then the ensuing flight depends on the following stick inputs, which are not recorded, of course. But it will have entered autolanding 20 seconds later, irrespective. It was flying under full forward elevator at around 4 m/s, and so could have travelled another 80 meters and then some more during descent if that stick input were maintained.

If the connection to the RC was lost then the aircraft will have entered the standard RTH protocol. But since the battery was already below the smart RTH level, I'm not sure whether it would attempt the 60 seconds retrace or simply go straight to RTH. Either way it would have switched to autoland after around 20 seconds. So it might have gone backwards at around 9 m/s (retrace), which would be 180 meters in 20 seconds ( the red pin) or backwards at a few m/s, since the wind speed exceeded the maximum positional holding speed and RTH speed. Those scenarios indicate looking back along the flight track around 200 meters or so, which would take it back to where it crossed the beach to the south, or in the direction of the wind field for around 100 meters (the blue line below).

That's a lot of places to look, unfortunately.