Commercial aviation encounters with severe low altitude turbulence
October 4, 2004
Turbulence encounters continue to be one of the largest sources of personal injury in both commercial and general aviation. A significant percentage of these encounters occur without warning, at low altitudes, and have been observed to occur outside of the strong reflectivity storm cores where pilots typically anticipate severe wind shear and/or turbulence. In this paper, statistics illustrating the altitude distributions of specific turbulence encounters are presented. These results suggest that a significant percentage of the moderate and greater turbulence encounters occur at low altitudes. One particularly dangerous form of low altitude turbulence, often associated with convective storms, is the buoyancy wave (BW). Observational evidence of commercial airline encounters with these phenomena indicates that they can cause an impairment of aircraft control that results in significant attitude and altitude fluctuations. Over the past two years several serious aircraft incidents involving low altitude turbulence have been reported. In our investigation of the meteorological conditions surrounding these incidents, there are strong indications that buoyancy waves played a major role in initiating the turbulence. While encounters with this type of buoyancy wave-induced turbulence can be as severe as microburst wind shear encounters, they are typically not detected by current wind shear detection systems. However, these phenomena do have detectable signatures. We suggest two modifications to existing wind shear detection systems that would make it possible to detect these potentially dangerous phenomena.