Quantifying Loss of Control Envelopes via Robust Tracking Analysis

Loss of control (LOC) occurs when an aircraft motion departs from the typical flight envelope. Loss of control events have been a contributing factor in numerous commercial airline accidents. Hence there has been interest in rigorously defining and quantifying the characteristics of LOC. One major issue is that LOC is rare and hence there is limited flight data for these events. This limits the ability to determine the flight envelope regions that potentially contribute to LOC. The basic premise of this paper is that a robust tracking analysis can be used to determine the permissible flight envelope. The motivation for this premise is that LOC is qualitatively characterized by inability to properly track commands. The paper formulates a robust tracking problem that can account for model uncertainty, key system nonlinearities, and time-varying trajectories through the flight envelope. Precursors to LOC are indicated by a degradation in robust tracking performance. The proposed approach is demonstrated via an analysis of a small, conventional fixed wing aircraft.