I have a friend who has a recital that I won't be able to attend due to a plane flight. I was going to send a message which ended with "I'll be cheering you on from the plane," but I'm not sure if "cheering you on" is appropriate outside of a sporting or competition context. My goal is to convey my support despite the fact I won't be able to attend the recital.
I see no problem with it.
Obviously if you were physically at the recital, you wouldn't cheer during the performance. But the phrase can be used metaphorically to refer to your encouragement. At a sporting event you would actually cheer to express them, but during a recital they're still in your mind. And those same thoughts can be in your mind on the plane.