Hi all,

I'm attaching my log from our last flight as our little quad went completly bonkers before it crashed.

Short after takeoff it went completly out of control, no response at all from RC or Telemetry and then crashed near a pond (thank god).

But the mistery was about to begin when we started reviewing the log and found out that the trigger was the failsafe error  Err: EKF_CHECK-2 / Err: FAILSAFE_ EKF-1. 

In understand these two were recently added to APM, but this ain't the first time I see this sort of thing happening.

I'm attaching my log in hopes for some guidance.

Thank you all!

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I also had an "EKF_CHECK-2" error yesterday in my logs. After a few seconds the error had been cleared (error code 0). This happened two times during the flight. The flight itself was normal, no loss of control, no crash, no failsaife. 

I am wondering, what has triggered this error code. I am flying an APM 2.5 without GPS (Quadcopter, Firmware 3.2).

All the best, Markus

I just had a similar issue. I've been having problems since going to 3.2. I had a mission that was configured to end with an RTL. I had the last way point less than 30 feet from the launch position, and was standing near the point. When it got to where it should have been landing it went in a different direction.

Last week, when I was flying a mission that I realized I'd planned as being longer than I wanted to, I sent the RTL command using channel 7. It was moving slower than I'd like, so I put it back in stabilize mode and drove it manually for a while, then flipped it back to RTL to make sure I was driving in the right direction. Somehow it seemed to change the launch location, and it landed on the other side of the field I was flying it in. I'd flipped it in and out of RTL several times.


Hi guys,

I have the same error.

I look at my logs and found the error was subsys:16 & ECode 2 & 0

By this list: http://copter.ardupilot.com/wiki/common-diagnosing-problems-using-l..., it's cause by EKF/InertialNav Check, Bad Variance.

So visit to fix this: http://copter.ardupilot.com/wiki/configuration/ekf-inav-failsafe/

I had the same thing on friday.
Was very suprised that without any obvious problem suddenly my quad went down from loitering in 3 m hight into a muddy meadow. Nothing I could do against it in that short of a time.
The gimbal and camera was deep in a puddle of water. You can imagine the effect.
I am using an APM 2.6!!! And the wiki says this great feature only works on a Pixhawk.
Whoever invented this nifty feature: THANK YOU! IT REALLY WORKS GREAT!
I simply dont understand it. When I fly behind my house, the copter has no problems at all. When I fly at my favorite flying site, I get several incidents of EKF_CHECK-2 with the corresponding failsafe. Today I was suffering 5 or 6 of these till my copter finally crashed. The gimbal got dislocated and hit the left front prop. Again, I am using an APM, not a pixhawk. As I understand it the APM should not even support this damn feature.

Hi guys,

I've had a incidents with this EKF_CHECK-2 too, and i see no reply to you, I had a new FPV transmitter,must have caused bit of noise, nothing too much, it seemed at one point in the logs,w hile i was doing a few very slow 360 turn , I got the EKF_CHECK-2 it caused the land, but really slowly,from a height, essentially nearly a flyaway,too dangerous, this is a crazy feature in 3.2. I should have stayed with the older code, there is to many new features for me and like this one its not documented.
As anyone an idea, why this feature is good, i read the page wiki, but think i need to look at the arduino code, I don;t understand logic how APM2.6 with an one external Mag checks against the inversence DCM.

Michael maybe there is power lines near by, up to 50 meter, you can get interference from a transformer near by, if i remember rightly. maybe triggering land mode.

Hi Steve,
thanks for your reply.
At least I did not see any power lines or transformers nearby. I was sort of in the middle of nowhere. I also do not understand why I need these features, but since I turned them both off, I have no problems at all.

Did anyone get an explanation of this? I keep getting errors like these and others and have had a run away quad 4 times now.. I don't trust it anymore and I can't seem to find or fix anything..

I appear to be having the same problem - see also :


Just had same issue and it forced the quad into Land mode in a bad spot. I don't even have EKF enabled, why would the EKF failsafe kick in??

wow...this is disturbing to read....serious bug for APM users if its not even a feature it can support yet is triggering a failure

I apologize, I should have clarified. I am running arducopter 3.2.1 on a Pixhawk with a F450 frame. I have EKF turned off and yet seeing an EKF failsafe error.  

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