Divergence Between Flight Crew Mental Model and Aircraft System State in Auto-Throttle Mode Confusion Accident and Incident Cases

In many aircraft accidents relating to pilot error, flight crews held an inconsistent assumption of the actual state of the system when reacting to a failure or abnormal situation. This paper formally defines divergence between flight crew mental model and actual system state, describes a developed framework to understand the mechanisms behind divergence, and discusses results of analysis of divergence in eight auto-throttle mode confusion accidents and incidents. The framework revealed that divergence occurred in all auto-throttle cases. As divergence was analyzed, it became apparent that reconvergence was also prominent in the accidents and incidents, where seven of eight cases indicated that the crew’s mental model and actual system state regained consistency at some point during the accident timeline. Success of recovery actions was dependent on the timing of reconvergence in relation to the criticality of the situation. Consistent with existing literature, the framework also revealed that breakdowns in situation awareness were apparent during the onset of divergence and as an inhibition of reconvergence. The analysis using the framework of divergence showed that for auto-throttle mode confusion accidents, mitigation efforts would be most effective if targeted toward promoting situation awareness of system state prior to the situation degrading beyond recoverability.