ThrOut 100% in Alt Hold issue

Hexa X F550, APM 2.5 w/ external GPS and compass, firmware 3.1.5.

After switching from Loiter to AltHold, after few seconds, copter began climbing at max throttle.
Then changed to Stabilize and hard-landed.

I’ve checks logs, baro and GPS is ok, ThrOut was 100% until Stabilize was turned on.

I can’t understand, what happened. Please, advise.

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Generally this is vibrations. Mounting your flight controller better should fix it.

No, this is not vibrations.

I was able to repeat this behavior, without props attached. After entering AltHold after few seconds ThrOut goes to 100% and stays there until flight mode changed, moving copter higher or lower do not changed anything.

I’ve reflashed APM and erased EEPROM, and problem is gone.

Will do additional tests to check if AltHold is working ok.

To be more clear, what I said was based on an analysis of your log. The baro alt runs away, and the inav alt doesn’t track it like it should.