Lost my drone, would appreciate any help figuring out what went wrong. Link to flight log below.



TLDR: Mavic Mini 2 Low Battery RTH (return to home) auto-triggered, but too late; it hit critically low battery on the way back; drone force landed in middle of the city and lost.

Questions:

• Why did RTH trigger so late? It has always triggered with sufficient battery and time to get back home safely. Why the failure this time?
• Did I do anything wrong? Should I do anything different in the future? I feel like I can no longer trust the auto RTH feature to work properly.
• Is this failure covered under warranty? I depended on the feature to work as expected, it didn’t, and the drone was lost as a result.
  

Story:

I was flying my Mavic Mini 2 around Mexico City from my rooftop. Had done a couple flights that day, and as always the Mini would auto trigger low battery RTH feature automatically, when it was time to return home, with plenty of time/battery to get home safely.

On my 3rd flight of the day, I was flying around the city, RTH auto-triggered when there was about 17% battery left. About half way back, it hit critically low battery and auto landed. I tried picking a big rooftop to land on so I can go retrieve it later. Signal and video feed was lost a few seconds before landing, so not 100% sure if it landed on that roof based on the video feed. Find my Drone shows it was on the corner of that rooftop. However, when I went to look and got access to the rooftop the drone was not there. I’m guessing either a) someone found it on the roof and took it b) it didn’t actually land on the roof, but on the street below, and someone found and took it c) it’s on a different roof/patio/tree in a dense city. I spent hours looking for it on the various roofs in the area, and have given up on ever retrieving it.



What happened? Did I do anything wrong? The “Intelligent Flight Battery” was not so intelligent this time. I don’t know how I can ever trust the low battery RTH feature again, lest I end up with another lost drone.



Here’s a link to the flight log https://drive.google.com/file/d/1AnzOJkx8QusfIYnU-7f0iysnVVZCVk4F/view

And a link to a logviewer on phantomhelp
https://www.phantomhelp.com/logviewer/VKV6RD3RQVPWQ3OIBSCA/


Edit: after taking a closer look at logs on phantomhelp, some timestamps of note:

• 16m 43.4s, 21% battery - Download link lost
• 17m 4.6s, 21% battery - Download link restored, A BUNCH of messages here including the first low battery message and enters Go Home mode
• 17m 21.1s, 18% battery - Drone enters sports mode after already being in Go Home mode due to low battery for several seconds. Drone not moving, just standing there, 0mph speed.
• 17m 31.3s, 17% battery - After 10s low battery warning and re-enters RTH mode.
• 19m 12.4s, 9% batter - Enters Auto-landing due to critically low batter.
  

A few things to note here

• I never received a Low battery warning on the controller at 17m 4.6s, when battery was at 21% (possibly due to connectivity issues?). I never received nor did I ever cancel RTH mode.
• The first low battery warning I received on the controller was when battery was at 17%, which corresponds to the 17m 31.3s message.
• Regardless, looks like it started to RTH at 17m 4.6s, battery quickly drains to 18%, enters sports mode but doesn’t move for 10s, then at 17m 31.3s is when I receive the first low battery warning on the controller and I accept RTH. From there on it’s in RTH until it forced auto-lands.
  

Appreciate any help. Thanks.

The link to your flight data is missing.
The data is essential for anyone to be able to look into your incident.

Find my Drone shows it was on the corner of that rooftop.

FMD can only show you the location information from when your app last had contact with the drone.
It can't show you where the drone might have ended up later.

What happened? Did I do anything wrong?
I can think of a couple of possibilities but need to see the data to confirm which or if it was something else.

Hello there francomini. I am sorry to read and to know what happened to your DJI Mini 2 and thank you for reaching out. Since this unfortunate incident happened and you have lost the said DJI drone. I would recommend for you to contact our DJI Support Team at https://www.dji.com/support?site=brandsite&from=nav for further assistance. We have a team that will do there best to help you and give out the best resolution for the said issue. Again, I am sorry and thank you.

Labroides Posted at 8-2 15:44
The link to your flight data is missing.
The data is essential for anyone to be able to look into your incident.

Labroides, Looks like i didn't Hyper link correctly.

Added the full links above and here:

Here’s a link to the flight log: https://drive.google.com/file/d/1AnzOJkx8QusfIYnU-7f0iysnVVZCVk4F/view

And a link to a logviewer on phantomhelp.com: https://www.phantomhelp.com/logviewer/VKV6RD3RQVPWQ3OIBSCA/

francomini Posted at 8-2 18:16
Labroides, Looks like i didn't Hyper link correctly.

Added the full links above and here:

At 1032.9 seconds the Mini 2 started Low Battery RTH/
Battery was at 21% and distance was 1710 metres.
In still air the Mini 2 would return at 10 m/sec and take about 3 minutes.
Nine seconds later, RTH was cancelled and the drone left hovering in Sport Mode for 10 seconds.
Battery down to 17%
Low battery RTH started again at 1051.4 sec and started returning at 10.4 m/s, which confirms that there was no headwind issue for the return flight.

At 1152.4 sec Critical low battery autodescent starts with the drone still 687 metres from home.
This was 120 seconds after the initial low voltage RTH warning
RTH should have taken 170 seconds (in still air).
The time between Low battery RTH warning and Critical low battery autodescent was insufficient for RTH.
There were numerous warnings during the flight that said:   High altitude. Aircraft braking distance increased and flight time decreased. Fly with caution

Perhaps that has something to do with the incident?
It would be interesting to hear DJI's explanation (if they give one).

When data stopped at 1202.8 seconds the Mini 2 was 4 metres above whatever was below it.
It should have landed safely, unless it was on the edge of the building or the roof was too steep.

Labroides Posted at 8-2 21:31
At 1032.9 seconds the Mini 2 started Low Battery RTH/
Battery was at 21% and distance was 1710 metres.
In still air the Mini 2 would return at 10 m/sec and take about 3 minutes.

Thanks Labroides.

I'm pretty positive I didn't manually cancel RTH once it started. Is there any other reason RTH would be cancelled and hover in sports mode for 10 seconds?

"confirms there was no headwind issue for the return flight".  
When there is headwind does the drone just keep using fixed power and therefore slow down OR does the drone use more power to try to maintain 10m/s speed (in which case it wouldn't be possible to tell if drone if moving 10m/s in still air or with some wind, but just using more power)? Do we know which behavior is programmed by DJI?

francomini Posted at 8-3 11:33
Thanks Labroides.

I'm pretty positive I didn't manually cancel RTH once it started. Is there any other reason RTH would be cancelled and hover in sports mode for 10 seconds?

I'm pretty positive I didn't manually cancel RTH once it started. Is there any other reason RTH would be cancelled and hover in sports mode for 10 seconds?
I can't think of any other reason RTH would stop or that the drone would go to Sport Mode.
That just doesn't happen by itself.

"confirms there was no headwind issue for the return flight".  
When there is headwind does the drone just keep using fixed power and therefore slow down OR does the drone use more power to try to maintain 10m/s speed (in which case it wouldn't be possible to tell if drone if moving 10m/s in still air or with some wind, but just using more power)? Do we know which behavior is programmed by DJI?
The more recent models will use additional tilt to go faster when that's needed to make headway against a strong wind.
But if the wind is strong enough to prevent the drone getting home before the battery runs out that's not enough.
But in your case there was no strong wind and wind was not a factor in the incident.

two things happened:

1. something, looks like user interrupt, caused rth to be switched to sport mode. which canceled the rth.

2. auto landing is actually flyable. you should have been able to fly it back  its just about half a mile left, sadly you lose it... the 5% power is more than enough to get it back if you know you can still use the sticks to raise the drone and fly fowards.

Labroides Posted at 8-3 15:04
I'm pretty positive I didn't manually cancel RTH once it started. Is there any other reason RTH would be cancelled and hover in sports mode for 10 seconds?
I can't think of any other reason RTH would stop or that the drone would go to Sport Mode.
That just doesn't happen by itself.

I got a response from DJI. Their conclusion: "incident was caused by not paying attention to the battery level". They're offering 15% off a new aircraft.

I do not agree with their analysis. I was paying attention to the battery level, but I was relying on the aircraft to auto RTH when it decided the time is right. From my point of view it triggered to late and caused the incident. That's on DJI. I understand to log shows RTH was cancelled and entered sports mode at some point, but I know I never physically cancelled low batter RTH. The only explanation I can think of is either I unintentionally cancelled it which seems highly unlikely as at that point I was flying via the screen and nothing popped up, or some bug in the software.

What do you guys think? I know I never cancelled RTH, but I understand the log looks like I did. Do I keep fighting? Is DJI usually understanding/lenient or strict with such cases? What else is there to say to them?


DJI Thread below:
----

1. The aircraft worked under GPS mode after it took off;
2. Flight Time T=12:04, Relative Height H=102.4 m, Distance to Home Point D=2094.2 m, Battery=45 %, Failsafe RTH was triggered due to the loss of the remote signal, which was canceled by the pilot; Failsafe RTH was triggered several times  and all canceled by the pilot;
3. T=17:39, H=113.4 m, D=1659.5 m, Battery=11%, RTH was triggered by the pilot via the remote controller and the aircraft started to Return-to-Home;
4. T=19:13, H=114.5 m, D=687.2 m, Battery=9%, Landing was triggered due to critically low battery level;
5. T=20:02, H=9.5 m, D=656.9 m, Battery=5%, the flight record ended due to the loss of remote signal. The aircraft was descending at 0.9 m/s and it would land at an improper place in the end;
6. The last recorded point: 19.4064851, -99.1809292.

According to the analysis, the incident was caused by not paying attention to the battery level. Please fly with caution.

**I challenged the analysis. Their follow up response:**

We checked the flight record for you again, the RTH was triggered several times, all canceled by the pilot, but the pilot did not control the aircraft flying back as soon as possible. T=17:11, the low battery RTH was triggered. The aircraft RTH normally. If the pilot cancel the RT, please make sure to control the aircraft flying back first.

francomini Posted at 8-25 08:54
I got a response from DJI. Their conclusion: "incident was caused by not paying attention to the battery level". They're offering 15% off a new aircraft.

I do not agree with their analysis. I was paying attention to the battery level, but I was relying on the aircraft to auto RTH when it decided the time is right. From my point of view it triggered to late and caused the incident. That's on DJI. I understand to log shows RTH was cancelled and entered sports mode at some point, but I know I never physically cancelled low batter RTH. The only explanation I can think of is either I unintentionally cancelled it which seems highly unlikely as at that point I was flying via the screen and nothing popped up, or some bug in the software.

I understand to log shows RTH was cancelled and entered sports mode at some point, but I know I never physically cancelled low batter RTH

As stated above, switching to sports mode will cancel! RTH no matter what, i only tried this 2 days ago, therefore you inadvertently cancelled RTH.

Not knowing the aircraft is the main cause here, you should read the manual a few times especially the RTH feature

Aircraft should be here

'...as always the Mini would auto trigger low battery RTH feature automatically, when it was time to return home, with plenty of time/battery to get home safely.'


Forgive me, but isn't this risky? I mean, flying until a low battery warning at that distance (1.7km)?

Stu.Baby Posted at 8-26 13:45
'...as always the Mini would auto trigger low battery RTH feature automatically, when it was time to return home, with plenty of time/battery to get home safely.'

With a decent battery, no wind, 20% battery should get you home in normal mode, maybe about 4 to 5% spare. So yes, risky...

As a new pilot myself these kinds of things still worry me. I've only ever used RTH once just to test it but am skittish about flying out so far that I get the RTH warning. My flights so far have been 10 to 15 minutes tops which includes manually flying back home so I usually have plenty of reserve battery to spare. After reading through manual, guides and watching videos I'm of the mindset that RTH is more of a last resort feature if you lose signal or can't get it back on your own for whatever reason. But that really sucks. Hope you get a better resolution to the incident.