Hello fellow Pilots. I'm new to this forum (and drones) and would like to ask for your assistance with determining cause of my recent unfortunate accident. I fixed the drone already but I'd like to know what exactly happened so I can avoid this situation in the future.
  

  During our holidays in Croatia I let my wife to fly drone along the coastline. Unfortunately she flew little bit to far - about 1km and turned the drone behind a cliff so it went out of sight. At this point drone lost signal with controller. I wasn't watching the app at the time but I was sure that drone will RTH as it happened to me before. On weak signal I always had a message on the app asking me if I want to start RTH and drone was doing that without any issues. Unfortunately this time my wife didn't get this message (so she says anyway) and we got only "Landing" voice prompt and then RC was continuing searching for signal. Soon after I managed to recover drone from the sea. I also managed to recover videos from SD card.
  
  From what I've seen:
   
   1. Recorded flight time until signal dropped was 5m20s
   2. When signal was lost, drone stopped and started hovering for about 24 seconds
   3. Then it started descending for 50 sec and stopped about 2 m above sea level
   3. It kept hovering for about 8m 30s and then landed in the sea
   
   We took off with full battery in decent condition (around 20 cycles). Can you explain to me why drone didn't RTH after loosing signal, how it was doing before?
   
   I suspect that it could be just wrong setting on RC signal lost but unfortunately since I didn't have time to go through all the settings before going on holidays I'm not fully sure how it was set prior to water landing. I checked it only after the repair and it was set to "Landing" but if it was set the same before I'm not 100% sure also as I noticed that some other settings like for gimbal for example have been changed/reset after the repair. And even if it was set to "Landing" that still doesn't make much sense to me as from the recovered video I could see that drone after loosing the signal was first hovering for about 24 sec, then started descending (or maybe landing?) but it stopped about 2m above the water and was hovering for another 8m30s before finally landing in the water. I'm not sure how this procedure works with "Landing" setting on. Would it prepare to land first, descend and keep hovering just above ground (or water) until battery is critically low? Or it should land immediately without any hovering?
   
   I would appreciate also if you could explain me one more thing to me. Few days before this incident I also experienced low RC signal and then I got a message on DJI GO4 app asking me if I want to start RTH procedure which then I had to confirm by sliding button on the app. Is it separate option from "RC signal lost" setting or is it based on this setting? I assumed that it's based on RC signal lost setting set to RTH but maybe I was wrong? Wish I had checked this setting before but now it's too late. Is it possible to check how it was set in the logs?

First, let me admit that I am not familiar with the Mavic Pro. But it sounds like you had it set to land instead of RTH. There are a few good reasons to do that, but not in this case. Next, I suspect the the drone recognized that it was not safe to land there after descending to within 2 meters of the water and prompted you for input, but since it was out of range you did not see that message. It landed after the battery level became critically low. Again I am basing this on experience with other DJI drones, not with the Mavic Pro.
Other more experienced members here may be able to help with reading the log file data.

Try posting your log here - http://phantomhelp.com/logviewer/

Can you explain to me why drone didn't RTH after loosing signal, how it was doing before?
Sure ... if you post your flight data.

   I suspect that it could be just wrong setting on RC signal lost but unfortunately since I didn't have time to go through all the settings before going on holidays I'm not fully sure how it was set prior to water landing.
Unless someone has changed the loss of signal action (almost no-one ever does), it would still be set to the default value of RTH.

I assumed that it's based on RC signal lost setting set to RTH but maybe I was wrong? Wish I had checked this setting before but now it's too late. Is it possible to check how it was set in the logs?
If signal was lost, you couldn't communicate with the drone to tell it to RTH.
Obviously signal was not lost at that time.
Yes, it's possible to see what it was set to in the flight data.

I don't have the pro but am happy you we able to find and fix it! Bravo to you my fellow pilot.  

DAFlys Posted at 10-16 00:19
Try posting your log here - http://phantomhelp.com/logviewer/

Thanks for the link.

Flight log below:

https://www.phantomhelp.com/logviewer/ATNB7MVX54H15BGOR14F

Just looked at it and it shows all flight data but I coudn't see any info on applied drone settings. Unless these can be found in DAT or CSV files?

5 min. 9.4 seconds. Remote controller auto landing started.
Never cancelled. Appears to be a wrong button pushed, and never checked.

Woytashek Posted at 10-16 12:55
Thanks for the link.

Flight log below:

Your flight data shows that you had the Loss of Signal action set to Land.
That's almost always a mistake, particularly when flying over water.

But it made no difference, because your drone never lost signal.
The data shows full signal when the drone started autolanding (because you pushed the wrong button), and for 11 seconds after until it splashed down.

Labroides Posted at 10-16 14:13
Your flight data shows that you had the Loss of Signal action set to Land.
That's almost always a mistake, particularly when flying over water.

"The data shows full signal when the drone started autolanding "
We've lost video signal for sure. Don't know if it's equal to loosing controls as well

"(because you pushed the wrong button), and for 11 seconds after until it splashed down."

You mean this button?

Correct me if I'm wrong but I don't usually see this button unless drone is close to the ground but at the time drone was hovering at least 20m above sea level


"Your flight data shows that you had the Loss of Signal action set to Land"

Can you tell me where do you see that in LogViewer? I tried to find it but I see only "Autolanding" Flight Mode started at 5m 9.4s but as I understand it's not necessarily the setting?

Although I wouldn't be surprised if it was set to that at the time as I mentioned before. That's why I'm trying to confirm it 100%. Are there any logs stored locally in the drone apart from logs stored in the app?

Woytashek Posted at 10-16 16:19
"The data shows full signal when the drone started autolanding "
We've lost video signal for sure. Don't know if it's equal to loosing controls as well

We've lost video signal for sure. Don't know if it's equal to loosing controls as well
The app was continuing to record flight data for 11 seconds after the autolanding started.
That can't happen if signal is lost.

Correct me if I'm wrong but I don't usually see this button unless drone is close to the ground but at the time drone was hovering at least 20m above sea level
The data confirms that you initiated Autolanding in Column Y (Line 2936) of the CSV file.

Can you tell me where do you see that in LogViewer? I tried to find it but I see only "Autolanding" Flight Mode started at 5m 9.4s but as I understand it's not necessarily the setting?
Column DL shows your Failsafe Setting

But there's one other factor that helped sink your drone.
You had a big lump of land between you and your drone.
That would have blocked signal when the drone descended lower than 3 metres below your launch point.
And on losing signal, that would have caused the set failsafe action to come into effect.
And that propelled the drone into the deep.

Woytashek Posted at 10-16 16:19
"The data shows full signal when the drone started autolanding "
We've lost video signal for sure. Don't know if it's equal to loosing controls as well

Hi Woytashek,

Had a look at your flight too, sorry for yor loss.

At the end flying at 10.1 meter baro height down link loss for 8.6 seconds.
But only the down link so commands to the drone still possible.
As your did....when fully connected again after the 8.6 seconds the height now 8.2 meter, so it was already descending due to the AutoLanding in progress.In those 8.6 seconds you must have selected land on the screen.....
In the log no value for pressing on the RTH button, so the message "Remote Controller Auto Landing Started" is confusing.

Or is the soft button on the screen only a LAND button if the FailsSafe action is set to LAND?, this i do not know....(not a Go4 user anymore)

During the autolanding again a down link loss for 2.3 seconds.
See your data in my chart.

If only you had pressed the cancel button during the last 11 seconds, to stop/cancel the autolanding....

Fail safe action was set to LAND, so if you had a full connection loss (flying out of the (radio) visual LOS) ; than your drone would land and not fly back home....

cheers
JJB

Thanks very much for your review and input guys - that makes it much clearer to see now what exactly happened and what caused this splash. Appreciate it!

To summarise - from your info and my video here's what I think happened:

1. My wife flew the drone into the bay - behind the cliff. At this point she completely lost video feed but not control (now I know that loosing just video feed is not equal to loosing control signal - lesson learned)

2. Auto-landing button was then pressed unintentionally.  She doesn't recall it - I don't neither but who knows. Maybe she did it unintentionally or in panic and dosn't remember? When I took over controller I was trying a lot of things to regain control. Maybe in rush I've mistaken Auto-land and RTH softkey - can't really tell now but TBH I didn't see Auto-land button that often when I was flying - unless I was close to the ground. Maybe it appeared on the screen at this point when it was hovering still very high. Still this wouldn't matter if not point 3!
3. RC signal lost setting was set to Land instead of RTH as you guys confirmed. Don't know why previous owner used it but nevermind - it was his choice. I should check it before flying but I simply assumed that it's set to RTH because few times before I've seen a prompt message "Low Signal - Do you want to RTH" (or something similar) and after confirming that, drone would return to home point. Now I know that it's completely separate option from RC signal lost setting. 2nd lesson learned.

Please feel free to comment if this scenario makes sense to you as well. I just uploaded Youtube video from this flight (and dive... ) so you can have a look also. Sorry in advance for the quality - I have very limited internet connection at the moment so couldn't upload original but you'll see easily what was happening with the drone.

https://www.youtube.com/watch?v=DqOpnlPu-2U

And just as a matter of curiosity - can you see in CSV file at which point we lost video feed? And at which point we had a voice prompt - "Landing"?

Woytashek Posted at 10-17 16:50
Thanks very much for your review and input guys - that makes it much clearer to see now what exactly happened and what caused this splash. Appreciate it!

To summarise - from your info and my video here's what I think happened:

Hi,

Had a better look in the log  after watching the video. so you did recover the drone and got the video off the sd card....
The moment speed decreases = the moment that a drone lost its connection to the RC. (as without conection drone stops flying and goes into hover)
In the log full forward stick is applied but speed start to decrease. from speed 9 m/s to 5.6 m/s with 100% forward stick in 1 second.So there must have been more than just a video down link loss! for a very short moment....no messages about disconnect or so, just not every 1/10 of a seconds records in the log.Another reason for slow down to a stop in braking for obstacle...but no messages about braking in the log.


That moment is:
4m38secs ; drone reduces speed. (still with full fwd stick wich is released after loosing video feed i guess) [ in the video at 2.21s ]
4m43secs ; drone in hover.

Autolanding started approx at 5m7 secs, Landing message on the screen or just few secs later. [ in the video at 2.51 ]

5m7s minus 4.38s equals 2.51 minus 2.21 (about 30 secs)

Visual in 3ChartInChart : top #1 red line = speed, #2 red line = drone pitch, #3 red line - RC forward stick.

cheers
JJB