Ace Combat Fan just posed a video showing an unwinnable softlock for doing the mission 20 tunnel run too fast. Figured this should be posted here so people know there is a limit to going fast. That said, huge props to anyone who can actually pull this off, that takes some steady and precise flying.

Long and short of it, make sure Count gets hit while you're in the tunnel segment or the drone doesn't spawn and you can't climb high enough to escape.