Throttle Failsafe in MANUAL?

During testing over the past few days, my aircraft has unexpectedly reverted to FBWA during MANUAL flight several times. It appears that there are brief lapses in radio communication (voltage drops? I’m still troubleshooting), and the throttle failsafe is triggering.

My question: the parameter description for FS_SHORT_ACTN and FS_LONG_ACTN specifically says that the throttle failsafe applies only to AUTO, GUIDED, and LOITER. Is this a mistake? Should this include all flight modes? I just raise the question to flag a potential mistake in documentation. Or perhaps I’m misunderstanding something. Thank you!

That sounds odd. Do you have a log you could provide to demonstrate the issue?

Here is one log. There is an uncommanded change to FBWA at about 5:55:20. This has happened on numerous flights.

I should add that I use a 2-position switch on the transmitter to select flight modes. On most of these flights, the Flight Mode parameters have been set with the first three in MANUAL and the last three in either LOITER or AUTO. FBWA was not on the list. That is why I’ve been assuming a failsafe mode was responsible, but perhaps there is an alternative explanation I’m missing.


Unless you’ve changed the defaults, failsafe for a plane will engage “circle” mode for 20 seconds then switch to RTL. It won’t switch to FBWA. I think you have radio control issues.

For the benefit of others who might encounter this thread in the future… I have spent a great deal of time bench testing failsafe modes and reading the source code, and now have an answer to my original question.

The ArduPilot documentation is incorrect. The failsafe modes do indeed trigger in ALL flight modes. In my case, FS_SHORT_ACTN was set to 2 (Glide), which puts the plane into FBWA with zero throttle. The only difference between AUTO/GUIDED/LOITER and other flight modes is how a FS_SHORT_ACTN of 0 is handled.

In AUTO/GUIDED/LOITER with an FS_SHORT_ACTN of 0, the plane continues in its present mode. In other flight modes, 0 is treated like 1 and the plane circles.