Translation:These airplanes are flying above the sea.
So... there wasn't a tips and notes section, so nothing was explained to me. hungarianreference.com says that fölé basically means "to above", but I still don't understand; when and/or why would you use fölé instead of fölött/felett? Does fölé basically imply that the subject wasn't above the other thing, but now it is?
I tried "These airplanes fly up above the sea," and it was rejected, in favor of "...fly above the sea." But the second one is ambiguous, it could mean flying toward a location above the sea, or it could just mean flying above the sea, that's just where the plane is, without any reference to getting there.
It's a correct sentence. Fölött and the other "static" suffixes and postposition doesn't exclude moving, but rather they say that the moving happens in one place.
"A repülőgép a folyó fölött repül" means that the airplane is currently flying above the river. With fölé it indicates that he plane was not above the river in the past, but is going to be above the river in the future. It's curently crossing the "not river"-"river" border.
Similarly "a szobában megyek" means "I walk inside the room" (i.e. I'm in the room and walk there) and "a szobába megy" means "I go into the room".