Safety Considerations for a Distributed Electric Propulsion Aircraft: Lessons Learnt from an Automated Flight-Test Accident Involving a Research Demonstrator
Characterizing the highly complex aero-propulsive interaction in distributed electric propulsion (DEP) aircraft may require automated flight-testing procedures with dedicated maneuvers, which introduce specific safety challenges. This paper investigates an accident involving a distributed electric propulsion research demonstrator, named SwitchMaster, during an automated flight-test mission for aerodynamic model identification. The event occurred during a scheduled pitch excitation maneuver and resulted in a loss of control followed by ground impact. The investigation is based on flight logs, telemetry analysis, and structured accident investigation methods, including the ICAO ADREP taxonomy and the Swiss Cheese Model. The results show that the accident resulted from a combination of open-loop control surface fixation, insufficient real-time safety barriers, ineffective maneuver interruption, and delayed recovery authority. Variable wind speeds and asymmetric trim acquisition are considered possible contributing factors to the aircraft drift from equilibrium conditions. This paper concludes with safety recommendations, software improvements and lessons learnt to enhance the reliability of automated flight testing for DEP aircraft.