Just back from a lovely week away in wales. Apart from a few hiccups with Mandy (Mavic Pro for those who are unaware).
First evening I took her out for a flight nothing unusual no wind very still. But coming back to me on rth and my app crashed, wouldn’t allow me any control on my joysticks or anything, shot off into the air and vanished way out of sight. After a few hours of tracking through fields streams bogs etc near where I was flying I couldn’t see her anyway used lost drone feature and got coords. After stumbling through brambles, nettles, more bog and to top it off cow poop I recovered her no damage whoop.
So day after took for a test flight everything working perfect no issues with app or controls phew
So went down to some waterfalls video them. Some great videos returned to home again fine.
Changed to a fresh battery walked to bottom of waterfalls sent Mandy out filming away. Finished and come to fly back manually, again app crashed (different device froze up) no control of drone on controller. Mandy shoots up and flys off right into trees, heart pounding thinking she would get stuck then falls out to my relief…well what I thought it was. I clamber over to find Mandy half in the water with it running all over half her body, her camera hanging off (ribbon snapped, and bracket that holds gimbal to shock absorber snapped, probable damage to video signal cable, missing prop, damaged landing gear at the bottom, and bottom plate few dints and bangs.)
I know how to repair the gimbal and shock absorber, got parts on order.
My only other thing is water damage what is the possibility of her surviving a swim? The battery was off when got to her, I unplugged straight away. Left to dry out for several days (no silica or rice as wasn’t at home) not tried battery or anything in her as gimbal still broke. Can anyone please give me some good news ?? Tell me she can survive this.
If I do manage to fix her I am going to fully wipe reinstall all firmware and reset all factory settings on app.
The app crashing won’t have prevented control … you can fly without a device attached at all.
Since it was in RTH mode, that would need cancelling first, before you would have stick control again.
Since it was in RTH mode, just letting it complete that would probably have been the best solution.
You can even turn off the RC and it will still complete the RTH … and, even better, if you’d managed to cancel RTH when trying to regain control, turning off the RC would initiate RTH again.
As to the wet and potential damage … that the battery was off is probably good.
You already know how to take the top shell off, so do that, and also take the base plate off … and then use a hair-dryer (just on warm, not too hot) to dry everything out from top and bottom.
Might be good to disconnect as many connectors as you can to prevent water lingering in the contacts, and liberal use of hair-dryer on all of them.
I have only experienced the app crashing on a few occasions over 4 years of flying and every single time it was the cable connecting the phone/tablet that was the culprit. I could still fly the drone using the controller to bring her back, I just didn’t have camera feed and maps etc. As for if she’ll work after her swimming lesson, it’s very much in the lap of the gods, it seems for every success story there’s a failure so until you dry her out and power up……fingers crossed.
I’ve looked into the ‘pack it in rice’ and it may work BUT you are far better putting it on a warm radiator and using a fan drive warm air through it.
Strip it as far as possible to make air flow as complete as possible.
Initial damage may have been caused by the battery still being connected but a bigger issue will be corrosion caused by slow drying and/or any contaminants in the water. Salt water being worse than freshwater.
Having been into the guts of an MP, I know just how many small multi-pin connectors there are, each of which has the potential to harbour water in the hundreds of pin-sockets for ages - and rice has absolutely way of drying out such locations.
As @FFf says, corrosion can continue in such places … corrosion that is exacerbated once in use again as a result of electric potential. Tracking as also a potential problem.
Before sending £1k’s worth of kit flying again, it only makes sense to do as thorough a job as possible, and since most of the MP will need opening up to replace the gimbal ribbon cable in any case, making a thorough job of it isn’t really that much of an additional problem.
All rice can do is (very) slightly reduce the humidity, it can’t “mop up” water from nooks and crannies.
Rice is better suited to things have few connectors and operate at lower voltages/currents, and that aren’t going to be flying.
Silica Gel would be a lot better than rice for many things - but even that wouldn’t really do what’s needed.
anyway used lost drone feature and got coords. After stumbling through brambles, nettles, more bog and to top it off cow poop 
I recovered her no damage whoop.