The easiest thing is probably to take them through a typical flight between airport A and airport B, encompassing a description of tower, approach and area and making the point that commercial a/c are generally under control the entire flight.
You could point out that according to V David Hopkin in Human Factors in Air Traffic Control, we have a lower critical error rate than any computer, but mention TCAS to make it plain that it's fairly difficult to ram a couple of aircraft together! You could also mention that scene in Die Hard 2 where the bad guys alter the glidepath and tell them it's impossible.