Three different aircraft..three different transmitter's? All PCM? Fail-safes set for low throttle & slight up elev? Or just the factory default HOLD on everything? Or PPM...How did each aircraft act, i.e. exactly like type radio and setup should act if R/F interference?

If you were using the same transmitter for all three aircraft I would naturally take a close look at it.

Great example for the application of synthesized channel select trans & receiver's... also having a portable frequency scanner handy to help confirm interference any sort of Outside interference.

Of course there is almost nothing you can do about shooters, I say almost nothing because a few actually have been caught in the act. True outside interference is very rare.. usually the problem will come from another modeler intentional or not. Shoot, I heard about one fellow on one particular day actually shot himself down!! Yep, two transmitter's same frequency... and yep he forgot to turn the other one off[&o]
Lee