Experimental Drone Variant 4J Loss of Navigational Control, Salisbury Plain, December 2025
Summary
The AAIB published a correspondence investigation bulletin detailing the loss of navigational control incident with an experimental drone Variant 4J at Salisbury Plain Training Area on December 11, 2025. The investigation found a fault in the navigation module caused the drone to breach its geofenced operating area, prompting emergency flight termination. The operator has implemented safety actions including fallback navigation logic and improved user interface alerts for positioning anomalies.
What changed
The AAIB published a correspondence investigation bulletin into a loss of navigational control with an experimental drone Variant 4J at Salisbury Plain Training Area on December 11, 2025. The drone lost command and control during a verification test flight due to a fault in its navigation module, which caused it to exit its geofenced area. Emergency flight termination was executed over safe ground and the wreckage was recovered.
Operators of experimental unmanned aircraft systems should note the root cause involved a single-point navigation module failure. The operator's subsequent safety actions—implementing fallback navigation logic and adding user interface alerts for positioning anomalies—may represent industry good practice for similar operations.
What to do next
- Monitor for AAIB safety recommendations
- Review navigation system redundancy
- Evaluate geofencing alert protocols
Archived snapshot
Apr 16, 2026GovPing captured this document from the original source. If the source has since changed or been removed, this is the text as it existed at that time.
AAIB investigation to Experimental Drone Variant 4J, (UAS registration n/a)
Loss of navigational control, emergency flight termination, Salisbury Plain Training Area, Wiltshire, 11 December 2025
From: Air Accidents Investigation Branch Published 9 April 2026 Category: Unmanned Aircraft Systems (UAS) Report type: Bulletin - Correspondence investigation Date of occurrence: 11 December 2025 Aircraft type: Experimental Drone Variant 4J Location: Salisbury Plain Training Area, Wiltshire Registration: n/a During a verification and validation test flight of a fixed wing UA command and control was lost. The flight was terminated when it was confirmed the UA was over a safe area. The UA descended to the ground and the wreckage recovered. A fault was found within its navigation module which caused it to breach the geofenced area in which it was flying. The operator has taken safety actions which introduce a fall-back logic within the system which can switch to other navigational sources and has modified the user interface to provide a clear alert to the remote pilot in the event of a positioning data anomaly.
Download the report:
Experimental Drone Variant 4J, UAS registration N-A 04-26
Download glossary of abbreviations:
Published 9 April 2026
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