Incident Overview
On 11 December 2025 at 1500 UTC, an Experimental Drone Variant 4J (serial PT-1046) was conducting a verification and validation test flight over the Salisbury Plain Training Area, Wiltshire. The aircraft was operated as a commercial UAS flight. No persons were on board, and no injuries were reported. The unmanned aircraft (UA) was destroyed beyond economic repair.
History of the Flight
Shortly after launch, the ground control station lost command and control of the UA. This loss led to the aircraft disregarding its preset geofence boundary. The remote pilot attempted to recover accurate navigational control but was unsuccessful. Once it was confirmed that the UA was over a safe area and not over a populated region, the operator initiated an immediate flight termination. The UA entered a vertical descent and struck the ground.
Technical Cause
An investigation by the operator recovered the wreckage and identified a fault in the 'in-house' navigation module that was undergoing testing. This module manages both visual navigation and fall-back logic to alternative systems such as GPS. The fault prevented the module from switching to alternative navigational sources, leaving the UA 'trapped' in a non-recoverable navigation state. It was not possible to determine whether the fault was hardware or software related.
Operator's Analysis and Safety Actions
The operator determined that the event highlighted a need for clearer pre-flight briefings on flight termination procedures and robust Emergency Response Plan training for remote pilots. A Safety Review Board mandated a staged return to flight to mitigate risks. Safety actions taken include integrating fall-back logic into the flight control system to allow switching to other navigational sources, and modifying the user interface to provide a clear alert to the remote pilot in the event of a positioning data anomaly.