unless the accident is the result of violating the law. Even then, it has only happened once, to my knowledge.
I think there are some prosecution once in a while, a recent case was the 2005 crash of Challenger at Teterboro, the accident uncovered the whole slew of shenanigans the operators of this flying outfit were engaged in, the judge threw a book at them.
A classic case that I recall was the sentencing to 18 months prison time of both MD-11 JAL pilots (in Japan) for causing 14 deaths in an accident that took place in 1997.