"I should add that RS232 is bidirectional, so that the Failsafe can send commands to the Autopilot, if desired.  This is intended to provide a mechanism for sending the vehicle home should one of the triggers be programmed for such an action…"

"@Randy, Thank you, and it is always VERY useful to hear early feedback, especially from people such as yourself. There are a lot of possible "automatic" triggers for various different actions, apart from the possibility of a direct command…"

"Hi Randy, I'll chip in a little.  A difficult decision when making an external flight termination device is how much complexity to allow.  Additional features (such as an IMU) do enable features such as you propose, but at the…"

"Can I add my 2c, bearing in mind that I know less than nothing about any APM ever constructed. I suspect the warning to not connect to the +5V pins has nothing to do with the APM, but is simply that the 3 pin connector from the sensor has a…"

"Hi James, Absolutely no offence was taken, and no apology is necessary, but thank you.And thank you also for your good wishes, very gracious. Cheers,Andrew"

"@James Cotton, Firstly apologies for potentially derailing this thread.I realise that your words were probably posted in frustration or anger, and are probably already regretted, but I thought it worth responding in defence of Kevin.I also realise…"

"Great discussion Matt!  Thanks for posting.  Sorry I do not have anything intelligent to add other than to say how enjoyable and educational it is to read a technical discussion. Cheers,Andrew."

"Thank you.  The command that is sent to the air vehicle is entered in a user field in the configuration software and stored in the flight termination device, so all of these possibilities are, er, possible.  Just wanted to know whether I…"

"The command he should send is MAV SET_MODE."

"I believe you can send a MAVLink packet that is the equivalent of the "PWM or PPM entering the autopilot" this is how MAVProxy can control the mode switch during simulations or when flying via Joystick *I think*. In the python code you see…"

"Perfect, thanks Bill and Kevin. Regarding monitoring of the telemetry uplink, I think the MAVLink uplink heartbeat should work fine, as long as it is sent often enough. The hardware will not have authority over PWM or PPM entering the autopilot, so…"

"I've written a GCS, so I'll give this a shot: 1) Yes - the GCS sends mavlink heartbeats (with the vehicle type listed as GCS) 2) For APM (at least) the sequence # matters if you are setting a new current waypoint (go to home would be…"

"Thanks for the clarification. :-) I don't see anyway around monitoring MAVLink Heartbeat messages. To trigger failsafe you can either send a MAVLink message to RTL, or you could set the mode switch PWM to correspond to the failsafe option i.e.…"

"Hi Bill, Sorry I should have introduced myself - I run Millswood Engineering.  Kevin contacted me a while back regarding flight safety matters and has been instrumental in encouraging and shaping a redesign of the current Failsafe board to be…"

"Hi Andrew, you should talk more with DS, he's giving away Millswood Failsafe devices see here and has some plans for an improved model to suit the DIY community."

"Thanks Bill and Drone Savant for the added detail. In fact the device that will be listening to the uplink and potentially sending a RTL command will be an update of this device. I would prefer to make the device protocol agnostic, hence the…"