Why did Ben not know about the plane?

Did anyone else catch in the last episode that when Locke mentioned that they were going to the plane that Ben asked him "What Plane?" and he replied "the beachcraft" and that they were going to meet himself. What I don't get is why Ben doesn't know about the plane but he has been in that station before that is under the plane. In the episode where the guys is hiding in the bathroom and Juliet and Ben come in and leave the walkie talkie they are in station that is directly underneath the plane. How could he have not known about the plane? What am I missing?

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