Oh you know, the commentary in Left4Dead talked about the helicopter pilot turning infected or something while flying the survivors out of the city and crash landed, but they didn't want to implement it because they felt it would hinder the player's feeling of success after fighting to get off the hospital. In fact, the pilot will sometimes mention that he had trouble when he made a stop on his way to pick you up.
Though since this is taking place between the two campaigns, it looks like they might be bringing it back?







