What damage can occur and what penalties will you face for flying a quad rotor into a restricted airspace?
The legal issues are covered in another question. The FAA doesn't currently regulate recreational model aircraft operations, which includes quadcopters.

Were you to actually fly it over the fence, you could be charged with trespassing. If you had any intent to cause harm, other charges might apply (up to attempted murder if you were trying to bring down an airliner).




  Can I crash a plane with it?


Not likely. If you flew the quadcopter into a jet engine intake, you might be able to shut down the engine (similar to ingestion of a bird). This would really annoy the flight crew but would normally not result in a crash. A strike in any other place is probably going to merely dent something on the plane, and utterly destroy your quadcopter. For a small plane, shattering the windshield is a possibility, and this would be a serious hazard that could cause a crash, but is quite unlikely. Without some kind of advanced guidance system, it's going to be very hard to hand-fly the copter into a plane at all, let alone precisely target a vulnerable point.

The bottom line, though, is don't do it.




  Is this a new terrorist attack vector?


Maybe! The use of unmanned aerial systems by terrorists is a subject of concern and research in the defense community. The RAND Institute has published a whole book about it.

Drones are already being used by drug cartels to smuggle drugs across borders. There have also been some high-profile incidents where terrorists were able to tamper with, and in at least one case eavesdrop on, a U.S. military drone by obtaining and decoding its live video feed. I don't know of any publicized instances of someone intentionally causing damage with a UAV or model airplane, but I'm sure the terrorists are thinking about it.