Jen. I think statistically, driving on the road is far more dangerous. Thinking about it, in 2007, the 1200 major airports processed 4.8 billion passengers and made about 32,400,000 flights. There are approximately 250 to 300 airplane crashes (aviation accidents) per year, but for ALL major airlines the average is about 100 to 120 deaths per year. (9/11 is very difficult to place in the assessment, making this number much higher.) You actually do have about 1 in 10 million chance of being killed in a plane crash and about 1 in 6,000 in a car accident.
You have more chances in dying by just driving to the airport!
(Some general statistics of interest here appear at ; http://www.planecrashinfo.com/cause.htm . This gives some detail on the chances by cause and during times of flight.)
** Errors for the results quoted above are fairly inaccurate due to the wild distribution of information. They are roughly in the ballpark though!