I think we have covered a lot of this already with the airplane question, but quite frankly, if fear comes up when you are dying in an accident you've got no hope. If we are thinking of a deadly accident, this is quick death, generally. You are not going to have any hope, the fear will overwhelm you, you will be caught up in fear and you may die screaming or whatever else. This is why you've got to practice now. You've got to practice with your fears, you've got to practice with your aversions, with everything else. And as I mentioned the Unpleasant Physical Sensations technique is a good one to work with in which you actually deal with some physical pain. The level of pain that can occur from an accident can get very intense, but you are not going to have time to think very much. You have to develop something that will come up spontaneously as I mentioned.
I was once in an accident driving a motorcycle on a dirt road. I was on my way home from work. It was late and just about dusk so it was starting to get dark. A cow jumped out of the long grass and the only thought that I can remember was the thought, "cow". That's it. I hit the cow, I went on the ground. If I did not have a full face helmet, one that covers your whole head, if I did not have that I would have lost my jaw because the guard was what slid along the gravel. It was that serious an accident that I could have easily died if I didn't have the helmet on.
The only thought that I had was one word - "cow". I didn't have any time to think or do anything else. Once I hit the ground my only concern was trying to protect myself. Fortunately, it was the coldest day of the year. and I had big, thick gloves on. If I hadn't had the gloves I would have lost all the skin on my hands, as well. I was fortunate.
In serious accidents the ticking of the clock is so swift, things happening so quickly, you'll need to have practiced before such an event and also made good Kamma in the past. If fear comes during an accident, you are probably going to die full of fear - if you haven't prepared yourself.