When there is a helicopter accident, the cause is most often linked to human error by the pilot, a mechanical problem, or an electrical malfunction. Although most aviation accidents are blamed on human error, in these cases, there are usually other factors in play. Human error could be decision-based, skill-based, or perceptual. In the case of a 2016 accident involving a helicopter air ambulance, which claimed the life of the four individuals on board, the pilot made an error when opting to carry out a mission despite weather condition ratings falling below minimum levels. Engine failure was to blame for a 2018 fatal helicopter crash in New York City, which resulted in five deaths. Two contractors were killed and a helicopter pilot was injured in Pennsylvania in 2018 after an accident involving workers stringing power lines.