I noticed that support for MAV_SYS_STATUS_PREARM_CHECK exists in the master branch on this commit. It appears that this commit has not made it into Copter 4.0.5. Is there a reason this has not been merged ? Is it possible to include this in the next release ? It would be really handy to be able to identify a prearm failure by looking at the MAVLink status packet.

That commit is part of and it should go in in 4.0.6 according to @rmackay9

That is wonderful news. It will be great to see your code make it into the Copter release. Thank you for your quick reply !