BACK functions as an edit exit when the white box is highlighting the airport identifier. I do see where it get stuck after entry of the digits so I'll have that fixed.
ENT is greyed out until the frequency is valid or three digits are entered.
I see how the 5400 doesn't allow the airport selecting doesn't work so I'll add that to the bug report.
Additionally, the ACTV button shouldn't be on the COM page so I'll have that removed.
Thanks Shawn, I am glad I was able to clarify the issues with the COM page.