The British have an association like our IMAA, but for extra big models called the Large Model Association. Their website is http://members.lycos.co.uk/LMASiteUK/ Very intersting stuff. One of their rules, which is tested at every event, is that turning off power to the transmitter should result in the engine shutting down completely. Starting from there, the cut-off for an engine becomes more than the mechanical problem of getting the thumbs on the switch on the model: which may in fact be at 500 feet over the crowd. Not strictly what this thread is about, but I can describe my solution to this with off-the-shelf stuff. I use a HiTec Eclipse 7-channel transmitter. Computer radios aren't for everyone, but this one work well for me in that the throttle movement is set with end points, and an even lower completely closed setting is associated with the throttle "cut" button on the transmitter. Hitting that button, instead of futzing with trim, closes down the butterfly and the engine stops dead, though there is still spark. Same thing can be done of course with throttle trim, but on my Eclipse I do not use throttle trim at all. Where the system becomes "failsafe", is my use of Multiplex receivers. I use the IPS-Mini 9-channel ($90 US from Hobby Horse) Instead of the PCM strategy, which requires a transmitter signal to do anything, you can set the exact servo positions on the Multiplex receiver, that should be actuated when transmitter signal is lost or corrupted. Set this - on the receiver! - for the "cut" position and the engine goes off when the transmitter goes off, and the Large Model Association rules are met. Another option, easily built, would be for the throttle pushrod to also disconnect the circuit to the ignition when travel goes that far (just a couple of strips of brass sheet that push apart would do fine). Anyway, I think the Multiplex receivers have been missed by people in all the hubub about PCM. It's ironic that HiTec has PCM now on the Eclipse, but also owns Multiplex. On these Multiplex receivers, a simple jumper-looking gadget is provided. You get any servo to the point you want it, pull the servo cable out of that channel, and put this jumper in then out, and the receiver is set on that channel. No fancy transmitters required, and really no fancy receiver, and you have a failsafe condition for when the signal is lost or some moron turns onto your frequency. It may be that the default you want in this condition is engine idle I just use this scenario to show how to get to the Large Model Association's rules with no special hardware or additional switches. In fact, the method people use of shutting down with trim on a non-computer transmitter can be emulated with the Multiplex receiver: just trim down before using the jumper. Then just switch off the transmitter and the engine quits. Long-winded. Sorry....I do that.