Low level operations come with elevated risk. An expert, well trained crew can do the same thing day in, day out, and yet have a bad day with very little change from what they were doing 10 minutes, 1 day, 1 year before. Within normal operations, functional resonance of factors associated with the process may just get to a condition where a number are near the edge, and enough together cause an undesired outcome. The operating environment is stochastic, around desired normal conditions, each of which has levels of variation that occur naturally, and are controlled in the course of the operation. Without going too far down the rabbit hole with that, note that the Reason model of causation, the "Swiss Cheese" model is simplistic, and assumes a linear process, and life is just not so. The final point is that the guys and girls that are out there doing this job are professionals, and face the risks that arise from their operation day after day.
R.I.P.
An accident in the real sense of the word. It is a job that is inherently risky and there is always the chance that there is going to be a small miscalculation that is fatal. No one would normally fly in those conditions if they could possibly avoid them.