Heat stress and helicopter pilot errors

Helicopter pilots are subjected to degrees of heat stress that under laboratory conditions result in decreased performance. However, the effect of heat stress on the frequency of helicopter pilot errors is uncertain. The purpose of this study is to determine whether there is an association between ambient heat stress and pilot error. The records of 500 helicopter accidents and incidents due to pilot error during the months May through October were selected at random. On the day of the event, ambient dry bulb and wet bulb temperatures were recorded and compared to temperature and humidity readings on 1000 days chosen at random over the same time period, after eliminating days where events occurred. There was a significant difference between the dry temperature distributions of the days with pilot error compared with the control group (χ² = 47.54, P <.0001). A dose-response relationship was found with a significantly lower risk when ambient dry bulb temperatures were 25 to 29°C (odds ratio, 0.6; 95% confidence interval, 0.5 to 0.8, P <.0001), an increased risk of 1.6 (1.3 to 2.0, P <.0001) at 30 to 34°C, and the highest risk at 35°C or more (6.2, 95% confidence interval, 2.1 to 21.8, P <.0002). There is a dose-response relationship between ambient heat stress and pilot error in Israel military helicopter pilots. This is the first study outside the laboratory showing a connection between heat stress and accidents due to human error. Further studies are required to substantiate our findings and to determine whether extrapolation to other settings is warranted.