Clint just offers a quiet smile as Howard chats, not bothering to offer any words of confirmation on Banner's status. He does seem awfully casual about the whole 'let's put the Hulk in a jet' thing, though, so maybe he knows something Howard doesn't. That or he's just disturbingly okay with it.

"I'm sure that can be arranged. If you can convince the boss it's essential for your research, you can probably even fly one yourself."