While I have said in the past that an AD was an ND, there are times that accidents happen and negligence was not in play.
We do accident investigation analysis at safety seminars for ballooning. There are some where negligence was a factor, and some where it was just an unexpected outcome of the event.
Examples are a pilot who lost his life a couple of years ago after he failed to look at the radar and launched in the face of a thunderstorm. The inflow sucked him into the storm, the balloon collapsed in the turbulence and he rode the basket and streamered balloon to the ground. He was negligent in not looking at weather conditions which had been in place all day.
Another is friend who had taken a couple of sponsors for a flight during a balloon festival. The wind was a little faster that day, but totally flyable. He went over the preflight with both people, had them review and sign the waiver. During the flight the winds picked up a little to around 10 kts. Still perfectly flyable, but on the edge of not. On landing the lady ended up with a broken ankle due to a little firmer landing. It was found out that she had a tendency to break bones, but that was not told to the pilot. The other passenger was fine. The pilot was not negligent in his planning, flying and landing, but unexpected circumstances lead to an accident between the slightly faster unforecasted winds and the lady's bone structure.