I was at the field 10/13/03 and one of the guys started getting hits and the plane was doing wild things and finally after a while it went in the ground. He said when he purchased the plane[RTf] it had a receiver for ch42 so he put 42 crystal in the radio, which was tuned for 38,how much problem would this cause. I know it is against FCC rules to do this. what does it do to the freq. when you change crystals in the transmitter.

With transmitters, they are tuned to their specific channel. If you change the channel, it's possible that the transmitter's output is off-channel slightly, or even "splattering" across several channels. The only way to check is to use a spectrum analyzer to see the actual output spread. The farther apart the two channels are, the greater the potential difficulty.

That's why the FCC has the prohibition.