Why did my Mavic Air decide to land on water?

fdewarren · Jan 5, 2019

Problem?

I cannot understand what went wrong. Pilot error, rookie mistake, interference ?

Was unit in a crash?
Yes, I think this qualifies as a "soft" crash since it landed on water and sank. After 10 hours, a diver was able to recover the unit but I don't think I will try to make it fly again.

What have you tried so far?
I have placed the Mavic Air in a rice box to get as much moisture away. It was in a river, so no salt water. Then I will probably send it to DJI with hope to find out what happened and maybe get a replacement unit. But first, I would like to understand what went wrong.
When the drone was recovered from the water, the battery was removed immediately, it still blinks but I do not dare try to charge it.

What device are you using ( iphone , ipad, Samsung , etc)?
Main controller is connected to an Iphone 8 using the side cable.

What firmware are you running (aircraft, remote controller)?
How can I find out since I did not record it and I do not dare to start the drone yet?.. Is it recorded in the flight log?

What Go app version are you using?
DJI GO 4 v4.3.9 (4269)

Any modification? (if so what)
no - Drone was purchased from an authorized DJI reseller on 23/11/2018

Did you change anything or install any apps? (if so what)
No changes whatsoever - I was still discovering the possibilities of the drone

Do you have a video or pictures of the problem? (if so post link)
I have the last flight log and the last video before I lost signal.
I was also able to recover all the photos & videos from the SD card but I did not record the screen since I was not going to do any special manoeuvers.
~~I do not have the video of the Mavic actually sinking in water otherwise it would be on YouTube already…~~

Link to the video: Link to the flight log video: Link to the last video of drowning (after repair):
And here is the narrative...

On January 4th I did 2 flights. The first one went well, no issue

For the second flight, I was at the top of a small waterfall. I used a fresh battery. I took off from a flat rock bed, used intelligent take off and the flight lasted 2 minutes 21 seconds. At that point, the drone was 10 meters away from home point and below at altitude -2.5m. It was in position to film my friends who were ready to jump into the water fall. So I decided to stop recording so I could start a new record file.

Just after I stopped the video recording, the screened showed a connection loss. I had visual line of sight with the drone which was still only 10 meters away. The antennas were perpendicular and as I tried to reconnect and could see the MA slowly descending toward the water about 3 meters below…

I was never able to regain connection, and it finally and slowly ‘landed’ on the water. Propellers stopped and it sank into the river. It was already 4pm so too late to dive (4 to 5 meter deep – no visibility). It was recovered only the next day at 7am.

Why did the remote loose connection just after I decided to stop recording? Is it an isolated event? I did a similar flight the day before at another location and it went very well. I did go below the home point in altitude and I did also stop and restart recording. I never lost connection.
It seems losing the connection triggered an auto landing where it was rather than a RTH. However, I thought such behavior was only if the drone is between 0-5m from home point. But It was 10 meters away, as recorded in the flight log.
Also, it was less than 20 meters from home point, so according to the manual, it should have returned to home at the same altitude. If so, because it was 2.5m below the waterfall, it would have hit the stones. But instead, it just entered into auto landing without moving, or retracing the route.
If you are wondering: I always use the mode RTH when connection lost (not hover or land).
Safe RTH altitude was set at 40 meters (confirmed in the log)
One more strange clue. On the recovered SD card, I have the last recorded video before the crash. Then there is one more file .mp4 that comes after (sequence number). I cannot read it. It is probably corrupted, but it is 253Mb and in the properties, it says it was created on 01/01/2000 at 00:00. Did the Mavic reset itself in mid-air??
I was able to repair the last video file from the SD, link above.

Meta4 · Jan 5, 2019

fdewarren said:
Just after I stopped the video recording, the screened showed a connection loss. I had visual line of sight with the drone which was still only 10 meters away. The antennas were perpendicular and as I tried to reconnect and could see the MA slowly descending toward the water about 3 meters below…

It seems losing the connection triggered an auto landing where it was rather than a RTH. However, I thought such behavior was only if the drone is between 0-5m from home point. But It was 10 meters away, as recorded in the flight log.

Also, it was less than 20 meters from home point, so according to the manual, it should have returned to home at the same altitude. If so, because it was 2.5m below the waterfall, it would have hit the stones. But instead, it just entered into auto landing without moving, or retracing the route.

I you are wondering: I always use the mode RTH when connection lost (not hover or land).

Safe RTH altitude was set at 40 meters.

One more strange clue. On the recovered SD card, I have the last recorded video before the crash. Then there is one more file .mp4 that comes after (sequence number). I cannot read it. It is probably corrupted, but it is 253Mb and in the properties, it says it was created on 01/01/2000 at 00:00. Did the Mavic reset itself in mid-air?

According to the manual:
Smart RTH, Low Battery RTH, and Failsafe RTH follow this procedure:
1. The aircraft adjusts its orientation.
2. a. If the aircraft is further than 20 m from the Home Point it ascends to the pre-set RTH attitude and then flies to the Home Point.
b. If the aircraft is between 5 m and 20 m from the Home Point it flies to the Home Point at the current altitude, unless the current altitude is less than 2.5 m, in which case the aircraft ascends to 2.5 m and then flies to the Home Point.
c. If the aircraft is less than 5 m from the Home Point it lands immediately.
So if your drone was 10 metres out, you wouldn't expect it to be autolanding on RTH.

As usual, the solution is most likely hidden in the recorded flight data.
Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
Come back and post a link to the report it gives you.

The final video file will be messed up because the file wasn't closed properly.

fdewarren · Jan 5, 2019

DJI Flight Log Viewer - PhantomHelp.com

So the question is: How does a Mavic behaves if connection is lost and altitude is negative within 5-20m from home point? It should rise to 2.5m right?

RayOZ · Jan 5, 2019

Yeah. Put the flight logs.
The second video, I didn't see any notification that it was auto landing. Was the downward sensors disabled? Maybe the water reflection was messing with it. How high above the water was it hovering before it started to descend?
Do you have DJI Care Refresh? Maybe send it in to DJI, if it was a malfunction, they would replace it for free.

fdewarren · Jan 5, 2019

The flight log link is in the message above
I am trying to repair the last video file I found on the SD maybe it will give more clues.
The recording of flight log stops when the remote lost connection. So no data about autoland is recorded.

Astom22 · Jan 5, 2019

fdewarren said:
The flight log link is in the message above
I am trying to repair the last video file I found on the SD maybe it will give more clues.
The recording of flight log stops when the remote lost connection. So no data about autoland is recorded.

I would post it anyway, I have seen guys get great info out of the flight logs time and time again. I would guess the loss of connection occurred due to something in the flight log and everything after was a result.

Post it and let the experts do their magic with it. I doubt you would be disappointed.

Spawn840 · Jan 5, 2019

It happen to me luckly i was right there to crab it . It was 5 to 7 feet above the water it i qas going to do a back and up shot an as i started up an back it stared to land a wiuld not stop. In the water for maybe a .5 sec. That was about 3 months ago many many many flights ago with not a bad flight after but i will not fly close to water again.

Meta4 · Jan 5, 2019

fdewarren said:
The recording of flight log stops when the remote lost connection. So no data about autoland is recorded.

There is no data after the lost connection.
What happened after that is only going to be on the internal data recorder.
The flight data shows your Mavic hovering for 10 seconds 10.1 metres from home and 2.1 metres below the home point.
VPS indicates it was 5.3 metres above whatever was below the drone.

fdewarren · Jan 5, 2019

Meta4 said:
What happened after that is only going to be on the internal data recorder.

Is this internal data recorder stored on the SD card? Because I have been able to retrieve everything that was on it.
Attached is the original log files from my phone (/FlightRecords)

fdewarren · Jan 5, 2019

I have been able to repair the damaged video file that I had found on the SD card.
It seems the Mavic Air did receive the command to start filming again.
We can see the aircraft hovering but going up slightly, then it went into some kind of autolanding mode until the end.
It looks like it is an autoland and not a RTH at the location, becaue the drone does not change its heading. If it was a RTH on spot, the drone would realign itself to the same heading it took off right?

Anyway, I hope you guys cn figure out what happened so I cn have a claim with DJI. I really feel I lost control and there was nothing to do. So frustrating, the drone was just 10 meter away!...

Meta4 · Jan 5, 2019

fdewarren said:
Is this internal data recorder stored on the SD card? Because I have been able to retrieve everything that was on it.
Attached is the original log files from my phone (/FlightRecords)

It's inside the drone - that's how it can keep recording after contact is lost.

fdewarren · Jan 6, 2019

Meta4 said:
It's inside the drone - that's how it can keep recording after contact is lost.

I was able to re-connect to the drone via DJI Assistant 2. It is amazing that it turned on!
I retrieved the flight log (flight record & sensing) from that flight which should be complete all the way to the end, but it is a DAT file and it seems only DJI can read these files...

fdewarren · Jan 9, 2019

While I wait for DJI to make a decision on my case, here is the video of the Mavic Air starting up, after spending 17 hours under water and 24 hours inside a rice bag!...

Mavic Air startup after 17 hours under water

fdewarren · Jan 11, 2019

Thank you for your support guys, this just landed into my mailbox

Your request（#1645268）has been updated, please reply the email below:
We're happy to inform you that we will cover the warranty for repair at this time. Please follow the guidelines below and route the unit to our facility.

I hope that by "repair" they actually mean "replacement" because atter 17 hours in water, there is not much that can be salvaged in the long run. I hope they replace the battery as well because it is dead.
No further explanation on the reasons for the disconnect and the forced landing.
Also, they don't seem to implicate the RC for the loss of connection.
To be continued...

Astom22 · Jan 11, 2019

fdewarren said:
Thank you for your support guys, this just landed into my mailbox

Your request（#1645268）has been updated, please reply the email below:
We're happy to inform you that we will cover the warranty for repair at this time. Please follow the guidelines below and route the unit to our facility.

I hope that by "repair" they actually mean "replacement" because atter 17 hours in water, there is not much that can be salvaged in the long run. I hope they replace the battery as well because it is dead.
No further explanation on the reasons for the disconnect and the forced landing.
Also, they don't seem to implicate the RC for the loss of connection.
To be continued...

I would bet money you'll be getting a brand new drone or at the least a refurb.

Simmo · Jan 12, 2019

DJI will not repair a water damaged drone. You will get a replacement.

fdewarren · Jan 12, 2019

I don't believe in a repair. I was lucky to be able to restart it just enough to retrieve the flight logs.
But new drone or refurbished drone, I really want to know what went wrong. I will be particularly careful about this RTH procedures on lost connection.

Meta4 · Jan 12, 2019

fdewarren said:
I will be particularly careful about this RTH procedures on lost connection.

There's not much to be careful about.
The default setting for Loss of Signal is RTH and it only changes if you change it.
And almost no-one ever changes it.

fdewarren · Jan 12, 2019

Well, I thought I had it figured out. But check carefully because there are different behaviors depending on the distance from drone to Home Point at the time of the connection lost.
In my case I suspect the drone decided to land because it was less than 20m from HP. But in the manual, it was supposed to climb to 2,5m and return to home.

fdewarren · Feb 13, 2019

All right guys! So for you who have been following on my little misadventure, I want to bring this to a conclusion.
I have finally received a new unit almost 1 month after the crash. There was some delay with DJI finding the drone after they had signed for it, then there was Chinese New Year, and then some more delay with FedEx when it took them 1 week to travel from Hong Kong back to Cambodia (versus 2 days with DHL the other way)
Anyway, I'm back in the air and first thing I did was testing the configuration.

In the range 5-20m, if you want the drone to come back to the Home point safe at +2.5m (as described in the manual) you need to activate the option "RTH at current altitude"
This is not described anywhere in the manual, but if you don't do that (like me) then on connection loss, the drone will behave the same as for 0-5m and it will land straight.

In that case, you better make sure there is no water within 20m of the Home Point!
Now, to be complete, I also tested what happens if the drone is beyond the 20m cercle. Well, even if you activate "RTH at current altitude" the drone will still climb to it safe altitude and RTH when you call for it or lose connection.

Now what remains a mystery is the complete loss of connection between RC and drone for the whole time it took it to land in the water (30 seconds based on the salvaged video)

So now you know, and me too. Be aware of that option.

By the way, at the sme time I have tested the situation when you set the drone to "hover" if connection is lost. After I selected that option (rather than RTH or land) I sent the drone about 30 meters away at a 10m altitude and I turned off the RC to simulate connection lost. The battery was already low but still in the yellow before the point of no return.
Can you guess what happened when it hit the low battery mark?
.

.

.

.

.

RTH at the safe altitude.

Another thing I discovered is that even during connection lost, if the drone detects that the surface below is unsuitable for landing, it will hover. During one test, I had to switch the RC back on to reconnect and see the message asking me to confirm landing. There was some tall grass underneath.
This tells me that the water surface was not detected during my incident or it did not consider it unsuitable... Even if on the video the drone seems to hesitate.