Filter-Based Detection of the Proximity to Loss of Tail Rotor Effectiveness within Helicopter Flight Data Monitoring

Loss of Tail rotor Effectiveness (LTE) is a critical low-speed aerodynamic flight characteristic that causes an unanticipated rapid yaw rate that will not subside on its own. Multiple factors influence this aerodynamic condition, like environmental conditions, helicopter model specifications and phases of flight. However, predictions of which of those elements cause a higher risk for LTE has not been determined as of yet. Because of this knowledge gap, pilots are often not trained well enough to proactively recognize the proximity to LTE, leading to several accidents in which the pilot fails to maintain directional control. This study begins to characterize the factors that contribute to LTE and the importance of this to helicopter safety. An LTE bowtie diagram is proposed to support hazard risk assessment and mitigation. The diagram is built through accident reviews and aims to give pilots a schematic summary of all the scenarios that may lead to LTE. Further, a new systematic filter-based framework able to detect proximity to LTE events within Helicopter Flight Data Monitoring (HFDM) is proposed. Safety-events detection is the main method of analysis used within HFDM. This method compares flight data to a large safety-event database, which includes predefined hazardous flight conditions and different levels of proximity to events. Through this framework, participating operators will be able to easily analyze data from multiple flights, visualize the results, and provide feedback to the pilots. This will promote pilots' awareness on the proximity to LTE during flight and educate them on conducting proactive LTE risk evaluations.