Easter egg: Region 2 - On the main menu, if you highlight the lower left screen, it displays one of those Satellite Navigation screens you can find in-flight. As with the 3D model this needs to be fast-forwarded.
Easter egg: Go in to the Bonus Features and then into "The In-Flight Movie: The making of Flightplan." Place the cursor on "D-Connectin Flights: Post Production" and press left twice and a little circle with a > symbol in it should appear. Click on it to hear the director talk about the post 9-11 movie problems.
Easter egg: I found this on the full screen DVD. When you're at the main menu, keep pressing your left arrow button until the leftmost screen (located on the back of the seats) lights up. I'm not quite sure exactly what it leads you to, but it appears to be a 3-D model of the plane. I had to press fastforward to get through it, because it does take a little while. It starts off in English, then cycles to what I believe is German.
Answer: The hatch they climb into is the hold of the plane, i.e., the section with the coffin, the car, and all the other luggage in. It only appears small because of the way it is filmed. As Kyle would have known, it would have been extra strong and reinforced, as it was a break in two sections of the plane.