Anyone looking for a challenge? I was thinking it might be possible to tap into the signals going to the LED and send back an audio tone via a spare tx channel. There should be a number of the old LED modules floating around now, so there'd be some to test with. The theory is you tap into the board itself where its sending the red and green signal to the LED (I'm assuming you can't use the wires themselves as it looks like a serial setup to handle both LED out and USB I/O). Feed that into an Arduino, and based on the R/G/RG signal generate a n audio tone that you send down a spare audio channel - I don't know if anyone actually listens to their camera audio. You'd have a constant beeping, but you'd get BVR feedback of GPS loss and confirmation of which mode you're in. If you wanted to be super-speccy, you could throw in a DTMF encoder / decoder pair and build a visual indicator that mirrors what's flashing on the Phantom.