I think that accidents being a part of real life should also be a part of AE
One way this could happen is that if you pay your employees badly then the quality of their work goes down which leads to a crash eventually
This would also discourage people from giving really bad salaries which right now just leads to a low employee morale rating.
And if a plane does crash not only will you lose the plane but reputation would go down and you would have to pay damages to victims.