What happened
On February 13, 2017, a PRIMOCO UAV MODEL ONE-100 (registration OK-X013S) was performing an automated flight from Příbram Airport (LKPM) using an automated takeoff mode. Approximately 50 seconds after takeoff, the aircraft's central processing unit (CPU) underwent an unexpected reset. This reset triggered a system transition to 'SAFE' mode and caused the engine to shut down. Although the pilot successfully restarted the engine and attempted to restore the flight mode, a second CPU reset occurred 50 seconds later, again resulting in an engine shutdown.
Due to the significant loss of altitude during these two power interruptions, the pilot was unable to recover the flight profile. The unmanned aerial vehicle (UAV) struck a forest area approximately 2 km northeast of the Příbram aerodrome at an altitude of roughly 50 meters AGL. The impact with the treetops caused severe damage to the airframe, including the fuselage, wings, tail surfaces, and the engine.
The investigation
The ÚZPLN investigation examined flight data logs, the autopilot unit, and the software. The investigation included ground-based simulations of flight conditions and laboratory testing of the VECTOR autopilot, including vibration tests and a 12-hour functional test. While the investigators were able to confirm the sequence of the CPU resets and the subsequent engine shutdowns, they were unable to replicate the resets during testing or identify the specific trigger for the initial failure.
Findings
- The primary cause of the accident was the loss of automated flight control functionality resulting from the CPU resets, which led to the engine shutting down during the climb.
- The system software was configured to shut down the engine simultaneously with a CPU reset.
- The pilot was properly licensed and experienced with this specific UAV type.
- The flight path planned for this critical flight exceeded the distance limits permitted under the pilot's current 'pilot-student' authorization.
- At the time of the accident, the operator's Operations Manual was still undergoing the formal approval process.