Factors associated with the safety of EMS helicopters.

The accident rate for emergency medical service (EMS) helicopters is thought to be approximately twice the rate for other commercial (Part 135) helicopters. This observation has led to numerous news reports and to the publication of conclusions of a National Transportation Safety Board investigation. The data for these reports come from investigations of EMS helicopter accidents and incidents. The authors surveyed all listed civilian EMS helicopter programs to examine both helicopter ambulance mishaps and the number of safely completed missions. Epidemiological methods were then used to compare the safety records of different groups of EMS helicopters. The single most important factor identified was the number of flights made by the program during the study period: busy programs had an eightfold lower accident rate (P less than .0005) and a three-fold lower total mishap (accidents + incidents) rate (P less than .0005) than less active programs. Programs with the ability to fly under instrument flight rules (IFR) at the pilots discretion had no mishaps (P = .044) during the study period. Multivariate analysis shows this IFR capability to be marginally significant as an independent factor (P = .099).