According to CNN, there was a plot, which was foiled, to blow up the fuel lines to JFK airport in New York. Story: http://www.cnn.com/2007/US/06/02/jfk.terror.plot/index.html
Can you imagine what that would've involved, had this actually been carried out? Just goes to show you, that even though we go about our daily lives, there's people out there working hard to kill us. Frightening indeed!