RE: 40 MHz - Is it legal in the USA for RC?
Even if 40 MHz is a public frequency and it’s not “illegal” for R/C I certainly would not stray from a frequency designate as an R/C frequency. The FCC has designated that frequency for another use. So the chances of brining your planes home alive are very slim.
Try Googeling 40 MHz under the FCC and see who you would be interfering with your flying.