Good post.
Counterterrorism officials have been concerned that terrorists might seek to use a wide range of vehicles and other instruments for attacks, from crop-duster planes and hazardous material trucks to underwater bombs carried by scuba divers, because they are generally subjected to less rigorous security measures than other industries.
Heres the incident I referenced in the above post:
Freeper/Author makes apology on Hannity radio show:
http://www.freerepublic.com/focus/f-news/1188906/posts