Epidemiology of Helicopter Accidents: Trends, Rates, and Covariates

Abstract

The objective of this work is to provide a better understanding of helicopter accidents (rates, trends, and covariates) and to identify areas that deserve careful attention for accident prevention. Several questions were here investigated, including: (1) whether there are differences in accident rates for helicopters with different number of main rotor blades? (2) whether different engine types are associated with different accident rates, controlling for number of blades? And (3) whether there are seasonality effects in helicopter accident rates? To this effect, Record Linkage of two Federal data sources, the FAA civil helicopter registration data and the NTSB accident data, enabled the investigation of these and other questions. First, the accident rates and trend analysis highlighted the safety challenges that continue to face helicopters (significantly worse track record than commercial airlines, passenger cars, and motorcycles). Second, it was found that helicopter accident rates vary by number of rotor blades. Third, one result upended traditional wisdom, which posited that reciprocating engines are associated with higher accident rates; in its stead, it was shown that helicopter accident rates vary with engine type and number of blades, and that turboshaft are associated with significantly higher accident rates than reciprocating engines for the 4-, 5-, and 6-bladed helicopters. Furthermore, it was shown that helicopter accident rates display seasonality effect. Statistical significance and possible confounders for these results were discussed. The issues here examined deserve careful attention from the helicopter community, and several topics were identified as important areas for future work. Any serious effort to improve helicopter safety will entail action on multiple safety levers, including design, operational, and policy/inspection-related ones. All of these actions should be evidence-based, and they will require better helicopter accident investigations and better flight data.