What happened
On February 29, 2016, a UAV Navigation Atlantic drone, operated by the Vlaams Instituut voor Technologisch Onderzoek (VITO), was conducting a test flight near Weelde, Belgium. The mission involved flying a predetermined path within a Temporary Segregated Area to test waypoint navigation. Shortly after takeoff, the aircraft experienced communication disruptions between the ground control station and the drone. In response to these interruptions, the autopilot initiated an automatic landing sequence. However, this landing procedure failed. As the aircraft reached its pre-programmed endurance limit, it deviated from its intended path and flew south. The drone continued at 4,000 feet until the engine ceased operation, resulting in a crash in a field north of Dizy-le-Gros, France. There were no fatalities or injuries reported.
The investigation
The AAIU(Be) investigation focused on the technical and operational circumstances surrounding the loss of control. Investigators examined the aircraft's hardware, specifically the radio antenna connections, and reviewed the autopilot software logic. The investigation also scrutinized pre-flight procedures and the crew's response to the communication loss. Technical analysis revealed that a poorly crimped antenna connector had caused the radio cable to disconnect internally. Furthermore, the investigation looked into the software modifications made to the autopilot to accommodate a transponder, which had inadvertently introduced a logic error.
Findings
- The primary cause of the communication failure was a faulty antenna cable connection caused by inadequate crimping.
- During pre-flight checks, the crew observed several communication interruptions but dismissed them as self-induced by their physical position between antennas, failing to perform the required connection checks.
- A software logic flaw caused the autopilot to revert to 'SAFE' mode and abandon the landing sequence when communication was interrupted, preventing the aircraft from completing its emergency landing.
- The aircraft's 'BINGO' time (maximum endurance) was reached, and because the landing had been aborted, the autopilot would not allow a re-entry into landing mode.
- Essential safety features, including the automatic parachute deployment, had not been activated by the crew prior to flight, and manual deployment was not attempted.
Safety action
Following the investigation, the manufacturer, UAV Navigation, confirmed it has updated its software validation process to better detect logic failures during communication losses. Additionally, the AAIU(Be) issued recommendations to review the 'BINGO' time logic to prevent loss of control and suggested that regulatory authorities review requirements for in-flight demonstrations following software modifications to proven designs.