High risk occurrence chains in helicopter accidents

We develop an approach to identify high-risk sequences of events (or occurrence chains) in General Aviation (GA) accidents using historical accident data. We demonstrate our approach on the 6180 civil helicopter accidents that occurred in the United States between 1982 and 2015. We begin by providing a detailed guide to the NTSB accident database including of the pre- and post-2008 coding systems. We compare the most frequently occurring chains for different mission types and injury severity levels. The single node inflight loss of control (LOC) occurrence chain appeared in 12.5% of helicopter accidents between 1982 and 2015, appearing most frequently in both fatal and non-fatal accidents. Students' (and sometimes instructors') inability to perform safe autorotations or improper autorotation recoveries most often resulted in hard landings. As a first step to reducing these unfortunate training accidents, we recommend conducting an in-depth study to identify high-risk training maneuvers and hazardous situations faced by student pilots. We provide recommendations to improve the NTSB accident database and recording system that could potentially help mitigate the top causes for GA accidents.