Take a real case:
Pilot is taking a few people on a pleasure flight. All his local operators have cancelled as the forecast is for massive cb's later in his area. His Chief Pilot checks the web and sees nothing on the satellite image, rainfall radar. He phones friends around the radius of where the flight is going to be. Nothing of note.
Flight takes off - then the cb's form and form quickly and densely. Pilot ends up crashing into the ground due to severe windshear and downdrafts trying to return to the airfield and breaks pasengers legs and puts people in hospital as well as destroying aircraft. But no fatalities. Fortunately.
Criminal or "an accident"?