Few days ago we were on a boat flying with our mavic air. Everything was perfect then I wanted to enter a more tight cave but it was still enough space to fly. Then it suddenly started to not following my commands of the remote. It was no longer under control, I let go of all the joysticks and it continued flying and crashed into a rock and fell into the sea. I didn‘t found it back.
So because I‘m making a film right now and need a drone, I ended up buying a new one. I bought a used drone from someone because he was only selling the drone without controller. So it was perfect because I only needed the drone.
Today I was flying with this new drone and it happened again. Everything was good and suddenly I coudn‘t control it anymore and it flew alone and crashed into the sand. It still works but I don‘t want to fly now anymore because I don‘t want to crash my drone again.
Anyone maybe knows what the problem could be?
Thanks

Upload your flightrecord (stored in a DJI subfolder on your mobile device) to this site and share the link with us: http://www.phantomhelp.com/LogViewer/Upload/
Then people can maybe say what went wrong.

Sorry to hear of your tumultuous flights.  I hope you are able to get back up and flying soon!  
In regards to your first flight and crash you mentioned in the cave..... Tight, dark spaces, with no view to the sky (especially with water beneath it) are a significant risk to drones.  DJI drones have 2 main methods for positioning themselves.  The first is GPS and the other is vision.  In a cave, there is no view to the sky so GPS signal won't work and it is dark, so the visual positioning systems won't be able to work either.  At that point, it won't be able to position itself and will likely drop into ATTI mode.  If you don't have any experience flying a quad-copter in ATTI mode, you will have a difficult time controlling it.  Especially in tight locations.
As was already mentioned, if you want further feedback (and not just guessing as I have done above), I'd recommend uploading your log file to the PhantomHelp site and pasting the URL here.  There are many experienced members that will have a look and provide feedback based on the evidence found in the logs.

Cheers!

Drone manual helps to prevent such situations ;)

Hi, sorry for the inconvenience. On your first drone. I would recommend syncing your flight records and contact our team for further help. I would recommend flying in an open area in which there are no interferences to avoid an incident. GPS signal might be interrupted as well if the aircraft is flying inside the cave and it will not recognize your command accurately or it may act differently. I would recommend using the drone in an advisable environment to avoid an incident. Please see the link for you to contact our support. Thank you.

www.dji.com/support

"Today I was flying with this new drone and it happened again."

Please tell me you didn't attempt the exact same flight and lost it in the same way.

DJKOR Posted at 2018-8-26 16:31
"Today I was flying with this new drone and it happened again."

Please tell me you didn't attempt the exact same flight and lost it in the same way.

Upload your flight logs so we can see what happened.
https://www.phantomhelp.com/logviewer/Upload/
Post a link to your log here

Fly inside to a cave. I think this is the reason why your drone lost control. No GPS in cave, over water and too dark for vision sensor. I am sure your drone switch to Atti mode and unable to keep on position. Once you release control it will drift until hit something. Please don’t try your second drone in there.

When you fly or when your drone goes into atti mode if you move your drone or its currently moving in a certain direction when atti mode is initialised the drone will continue to move in that direction under its own inertia.
I strongly recommend that you practice flying in atti mode and make sure you become very good at it before any attempts are made to fly inside a cave.As already mentioned by others you will not have gps and your vision system will not work therefore atti mode is your only option if you must fly inside a cave then you should be aware that this is going to be the case and you should be prepared for it prior to your flight.

Is it possible to practice with Mavic Air in Atti mode? How?

You better buy a cheap toy drone to practice Atti mode. Use a $1000 drone to practice something risky is not a good idea.

You must be kidding? Take up golf son, you're not fit to fly!... ever!!

The best drone to practice Atti mode is Inspire. If you not doing right it will cut your head off

Vendex Posted at 2018-8-26 14:11
Drone manual helps to prevent such situations ;)

Experience and common sense deals with the rest.....

GDL Posted at 2018-8-26 18:52
You better buy a cheap toy drone to practice Atti mode. Use a $1000 drone to practice something risky is not a good idea.

Stick to a Tiny Whoop maybe

The second time it happened I was in a wide open space on a beach no caves no obstacles that was what confused me
On my first crash I was pretty sure it was my own fault because of the tight space I was flying in but the second time I don‘t get what happened I will upload the flight record

Yesterday KP index is 7 and should not fly drone. The GPS signal is affected. My MA also has problem to position accurately in flight. You may try again in open and save place.

http://www.phantomhelp.com/LogViewer/DA4993CV8LYZ8SWLTILD/

This is from the cave crash

Pilot (and I use that term loosely) error! Move on! Nothing to see here!

http://www.phantomhelp.com/LogViewer/W4AOTXI9RF4DRN30DCRS/

This was from the second one
But I think I see the problem there is no GPS but I'm afraid the GPS of my new drone don't work because it can't find GPS nowhere

U were flying in ATTI mode!!!

Okay I see it was my own fault but can someone explain me how to avoid atti mode?

Dont fly into caves

Wait on open space until MA in GPS mode. Green flash light on back and GPS satellites over 10.

Higher Vana Posted at 2018-8-27 01:23
Okay I see it was my own fault but can someone explain me how to avoid atti mode?

Stay in clear LOS with the satellites ie DON’T FLY IN CAVES!

Is it normal that my drone finds like 11-13 satellite connections and then suddenly it has 0 satellites? Because when this happens when I´m flying it willl turn to atti mode if I understood that correctly

InvisibleName 7 Posted at 2018-8-27 01:35
Stay in clear LOS with the satellites ie DON’T FLY IN CAVES!

I get it okay but even in wide places my drone loose satellite connection?

That second log. I'm not sure what's going on there. The timer starts at 7 minutes and some things are messed up. Was this the drone that you said you bought second hand?

Edit: I do see the serial number of the drone in the second log is indeed different. Looks like you took off before obtaining any GPS lock and it never got it because the sky was not clear, you didn't let it sit in the same place for long enough to lock, or it was a faulty drone from the beginning. I'm leaning more towards the former however the discrepancy in the timestamp is a little strange to make the latter a possibility.

Sorry to read that mate

DJKOR Posted at 2018-8-27 03:18
That second log. I'm not sure what's going on there. The timer starts at 7 minutes and some things are messed up. Was this the drone that you said you bought second hand?

Edit: I do see the serial number of the drone in the second log is indeed different. Looks like you took off before obtaining any GPS lock and it never got it because the sky was not clear, you didn't let it sit in the same place for long enough to lock, or it was a faulty drone from the beginning. I'm leaning more towards the former however the discrepancy in the timestamp is a little strange to make the latter a possibility.

yes thats from the drone I bought second hand
I tried now some more times in the beginning there is no GPS and I have to wait like 5 min then it gets GPS is that normal?

Your stick shows full throttle in the first log.....29mph in a cave with NO sats in ATTI...  

Randy

Higher Vana Posted at 2018-8-27 01:16
http://www.phantomhelp.com/LogViewer/W4AOTXI9RF4DRN30DCRS/

This was from the second one

Never buy cheap, you will pay twice as much. Sorry for your unlucky purchase

CoreyB10 Posted at 2018-8-26 23:30
Experience and common sense deals with the rest.....

True, true ;)