First off, to file a lawsuit, victim's families must give up their right to the government's settlement package. One or the other.
Secondly, (a little legal stuff here): To win a negligence cause the plaintif must prove that the defendant owed a duty to the victim/plaintif to conform to a specific standard of conduct for the protection of the plaintiff against an unreasonable risk of injury, that duty was breached, the breach was the actual and proximate cause of the injury and there were damages resulting from the injury.
To win a case against UA (mind you I do criminal law, so don't take this as gospel), a victim's family would have to prove that UA was somehow negligent. UA owes each one of its passengers a duty to operate with a reasonable standard of care. Did UA's actions fall below that standard which resulted in the deaths? UA will say that they operated to the industry and FAA standards, so the answer is no. This reasoning is extremely powerful, but not bullet-proof (just because "we and everyone else has always done it this way" doesn't always mean they should do it that way. whatever "it" is. think dumping waste into drinking water)
That's a real basic way to look at it. Of course there's lots of other factors, but that is the basic question of law in a wrongfull death action. Torts is a semester-long class and just begins to touch on all the issues a case like this would involve.
