Hey Spook,
don't know why FS20 is so picky, when it comes to entering values.
Anyway, savest way is to double-click the current value so that it's underlayed in blue, and "physically" enter the value "0" (or any other value smaller than 20) rather than hitting the delete key.
When done put the mouse cursor into either one of the other fields and the copilot should dissappear.