Hello all!
I’ve got a Pixhawk still running ArduPlane V2.78b in my Skywalker 1900.
I land my plane in a grassy field in FBWA pretty much every time. Every so often, I have a hard landing (in that the plane drops vertically from roughly 1-2 feet off the ground, usually because of a stall) resulting in the pixhawk beeping a sequence of three beeps: LOW, HIGH, HIGH, with a ~10 second pause between sequences. A video of this is available here. I did not find this sequence documented in the manual or forums (or maybe I completely missed it 
.)
Along with this beeping, the Pixhawk becomes unresponsive to anything but manual control, and the Mavlink connection is lost. Flipping the mode switch around will not return me to FBWA and Mission Planner starts speaking “warning: no data for # seconds.” I still have full manual control of throttle and all control surfaces.
Unplugging and re-plugging the battery yields a normal boot up and restores functionality.
Some things I wish I had done are check the status LEDs on the Pixhawk and safety switch, as well as attempt to cycle the safety switch.
I do not have access to the .log at the moment, but I do have the .tlog, which I have attached. Right around 99.64, I plop down and everything stops updating. My guess is that the .tolg won’t be very useful in this case. I’ll upload the .log from the plane as soon as I can get my hands on it.
Thanks,
Muhammad Al-Rawi