What happened
On 11 December 2025, an Experimental Drone Variant 4J was conducting a verification and validation test flight within the Salisbury Plain Training Area in Wiltshire. The aircraft was being operated as part of a commercial UAS operation. Shortly after takeoff, the ground control station lost command and control of the aircraft. This loss of link resulted in the drone disregarding its established geofence.
After confirming the aircraft was positioned over a safe area and not over any populated regions, the remote pilot initiated an immediate flight termination. Following this command, the drone entered a vertical descent and struck the ground, resulting in the UA destroyed beyond economic repair.
The investigation
Following the incident, the operator recovered the wreckage to perform a technical analysis. The investigation focused on why the aircraft failed to maintain its flight path and why the geofence was breached. The examination of the aircraft's systems revealed a malfunction within the proprietary navigation module being tested. This specific module is responsible for managing both visual navigation and the transition to secondary systems, such as GPS, during signal loss. The investigation could not definitively conclude if the failure originated from a hardware or software defect.
Findings
- The primary cause of the incident was a fault within the navigation module.
- This fault prevented the system from switching to alternative navigational sources.
- The failure left the aircraft in a non-recoverable navigation state, which directly led to the breach of the geofence.
Safety action
To prevent a recurrence, the operator has implemented several technical and procedural changes:
- Integration of a new fall-back logic into the flight control system that allows for switching to alternative navigational data sources.
- Updates to the user interface to ensure the remote pilot receives a clear alert if a positioning data anomaly is detected.
- Implementation of a staged return to flight protocol.