Defining Commercial Transport Loss-of-Control: A Quantitative Approach

Abstract

Loss-of-control (LOC) has contributed to more fatal commercial airliner accidents and related loss of life than any other factor during the last ten years of worldwide operations. In 1997, the Commercial Aviation Safety Team (CAST) designated LOC as one of three major areas of concern in commercial aviation safety, and launched an industry-wide effort to define its causes and develop interventions to reduce its occurrence. But what constitutes “loss-of-control”? The question is not merely academic – the statistical nature of accident analysis requires that investigators group accidents by category. In some cases, the distinction between LOC and other categories, such as Controlled Flight into Terrain or Approach and Landing Operations, is unclear. In others, LOC is undoubtedly a factor, but its specific characteristics are so complex that they make analysis difficult. Consequently, investigators have called for the development of quantitative LOC measurements and criteria. In 2000, the Boeing Company and the NASA Langley Research Center jointly developed a quantitative set of metrics for defining LOC through a NASA-funded partnership under the Aviation Safety and Security Program. These metrics take the form of five envelopes relating to airplane flight dynamics, aerodynamics, structural integrity, and flight control use. These envelopes have been employed successfully in ongoing NASABoeing LOC research to indicate in a measurable sense whether LOC was a factor in an event, and to determine its onset and severity. When these criteria are used in conjunction with data from LOC events and aggressive flight test maneuvers, it becomes evident that the excursion of three or more envelopes is a reliable, quantitative indication of LOC. Furthermore, this numerical methodology can reveal new insight into the circumstances involved in LOC events, providing a valuable tool for investigators seeking viable safety interventions to reduce their occurrence.