This is a rather strange one IMO...

I never experienced reliability problems with the OTG cable connection over land, even flying well over 1km away.

However, recently I experienced a problem where the DJI Go App stops communicating with the RC via
the OTG cable when the Spark is flying over water (and well over 15m above the surface). The RC remains
connected to the Spark and I can controll it using the RC but the DJI Go App says it is disconnected and thus
I do not get video nor any telemitry, which obviously makes controling the Spark very difficult when 500m+ away.
In once case I had to press RTH on the remote just to get it back because I could not see it.

Simply unpluging the OTG cable and back in again did not resolve the problem. Nor did restarting the app or phone.
I had to power down the RC and power it back on again, which means this is not something that you want to do in flight.

This has happend to me several times over two different lakes and then I've flown many times since then over
land without any issues at all, as usual. I have also flown over another large body of water (but taking off from a hill above it)
without these problems.

So it is either an odd co incidence or is somehow related to the RC being very close to the body of water itself at ground level.

Anyone else experience similar problems?

I should also point out that in all cases I was way out in the wilderness with no known interference (I was too far away from civilization for that).

Here's a photo taken at one spot where it happened.

Whatever the reason might be, I find it hard to believe (not to say impossible) that it might be related to the OTG cable.

I have witnessed the Go App crash mid flight with an OTG cable.  This has only occured twice with me. Since having the experience I have evolved a way of connecting the OTG cable when changing batteries.  When I change a battery, I switch off the RC, close the Go App and then FORCE CLOSE it.  I use a Samsung Galaxy S7 edge and even though I close the APP it still remains in memory.  When I FORCE CLOSE the App and power everything down, I get a clean connection with the APP when I open it again.

Maybe worth a try

TranceMist Posted at 2017-10-12 12:01
I should also point out that in all cases I was way out in the wilderness with no known interference (I was too far away from civilization for that).

Here's a photo taken at one spot where it happened.

Your in a big valley maybe this has some effect on signal, can’t imagine it has anything to do with water.

The problem is between the phone and the RC, which are connected by cable. He says the RC still controls the AC. So it's not a signal problem.

Transmist:
To me that sometimes happens over land too. While I can't rule out my old phone as a contributing factor, your phone is newer and better than mine.
Let me ask you a few things:
1. How is your phone doing in terms of free memory (on the phone itself, not the SD card if you have one)?
2. Do you switch off bluetooth and WiFi when you fly with OTG?
3. Do you force close other apps before running Go4?

Not sure if that is a question for me to answer but if it is answers below.

Let me ask you a few things:
1. How is your phone doing in terms of free memory (on the phone itself, not the SD card if you have one)?
No issue, photos on SD card, phone has 64gb
2. Do you switch off bluetooth and WiFi when you fly with OTG?
Put phone in Flight mode
3. Do you force close other apps before running Go4?
Nope, just Go 4

djiuser_Kf4iPA3 Posted at 2017-10-12 14:03
The problem is between the phone and the RC, which are connected by cable. He says the RC still controls the AC. So it's not a signal problem.

Transmist:

I'm using an iPhone 7+ with 256 GB of storage, 47 GB of which is free. iOS 10.3.3.
I was in airplane mode (so Bluetooth and WiFi off).

I don't bother killing other apps as iOS manages this very well and the iPhone 7+ has 3 GB of RAM.
I've never had a problem with the DJI Go app crashing on me (I read a lot about this happening on Android), or any other performance problems with the app.

Really I think it's a case of the RC no longer wanting to communicate over the OTG cable (even though it is still controlling the Spark).
Note that I did mention that even rebooting the iPhone, or unplugging and plugging back in the cable
does not solve the problem. Only rebooting the RC solves the problem (but you must land first).

Anyway, I was just curious if others have experienced this particular issue and it does not seem so.
I will just have to see if it happens again and then gather more data.

Thanks.
I didn't see you mention it, maybe I missed something. But... have you tried different cables?

I know it probably isnt the problem but I would kill those other apps in the background.  IOS is great and all but I have seen plenty of problems with apps and settings, and they were solved by closing all my other apps or deleting a glitchy 3rd party app.

My experience is that an iphone works well on wifi connection with the current software.
So I have stopped using OTG. And  as a bonus, the function button assignments are remembered.
P.S. Nice picture!

I fly out over the water for just about every flight I have flown using an Android Samsung Tablet Ver 7 with OTG to the RC.  Been out well over a mile with no problems.  I even did a test over water at low altitude and was able to fly at .5 meters for long enough to see if Spark could see the water and hover in place and move around slowly without having altitude issues.   I've flown at 5 meters over water for extended periods to take some Circles and Spiral shots of my "pet" Blue Herons.  

Is it possible you have a faulty cable or a connection that wasn't solid?  When I fly without OTG the video feed is very poor with a lot of lag and break ups.  With OTG it is rock solid with an occasional blip in the video feed when I stop too or change directions too quick...but normally just a second.   I also have never turned off Cellular data, Wifi or GPS on my tablet while flying with OTG, don't know why it would make a difference if you were using the OTG.  I tried shutting off everything but wifi when using the table without OTG and it didn't make any difference at all.

Thanks for all of the responses. I've done many more flights over water now, with and without the OTG cable and have not had this problem again.

TranceMist Posted at 2017-10-12 12:01
I should also point out that in all cases I was way out in the wilderness with no known interference (I was too far away from civilization for that).

Here's a photo taken at one spot where it happened.

I want to go there!!!!


p.s. Sorry for the problems you experienced.  

TranceMist Posted at 2017-10-13 05:25
I'm using an iPhone 7+ with 256 GB of storage, 47 GB of which is free. iOS 10.3.3.
I was in airplane mode (so Bluetooth and WiFi off).

airplane mode can still have bluetooth active , i mention this as i had similar problem with dissconnectand my wifes phone was close by ,so when i checked mine the airplane mode was on but so was bluetoth, so switched that off too and it stopped disconnecting ..hope this helps

TranceMist Posted at 2017-10-12 12:01
I should also point out that in all cases I was way out in the wilderness with no known interference (I was too far away from civilization for that).

Here's a photo taken at one spot where it happened.

I have never had this kind of issue as I never fly with OTG eventho I bought one with my combo, but realized that DJI do not support the use of it anylonger...sooo...just waiting for DJI to support it back again.

And what I really wanted to say was, AWESOME picture...looks like a very beautyfull place...

Make sure that your phone isn't connected to your Spark Controller via Wifi while your OTG Cable is connected. If so, press the 'forget' wifi connection on your phone (in your actual phone Settings) to remove the wifi connection because it will conflict with your OTG connection even if your Wifi connection to your phone is already turned off. And be sure that your phone has the proper settings set for your spark and that your developer option in your phone is turned off. Hope this helps!

TranceMist Posted at 2017-10-12 12:01
I should also point out that in all cases I was way out in the wilderness with no known interference (I was too far away from civilization for that).

Here's a photo taken at one spot where it happened.

Stunning image.