Either 1. you have watched some disaster move or 2. you have watched news or remembered 9/11 or.
you may have insecurity in your life. Airplane symbolizes difficulties, problem you have in life. Crashing could mean criticism you are taking in reality. In this case, you probably lose control. This dream reflects your helpless conscience.
I've had a few dreams like that also. It could mean you just don't want anything to happen to the people in the plane, or on the ground. It may also mean that you had a premonition of what may happen in the near future. I hope not. Just go to bed with good thoughts, and I'm sure you won't have any more bad dreams like that.
watching Donnie Darko again?