What happened
On September 13, 2017, a W3WA Sokół helicopter was performing factory flight tests of newly installed NAV/COMM equipment. The flight crew, consisting of two experienced test pilots and a flight test engineer, was operating the aircraft on its final leg toward EPSW Świdnik. At 18:12 LMT, the aircraft experienced an excessive desynchronization of engine torques while operating in PRIMARY mode. The issue persisted even after the system transitioned to BACK-UP mode, forcing the crew to perform non-standard procedures to manually control the NR2 engine. Due to the unusual behavior of the FADEC system and the aircraft's proximity to EPLR Radawiec, the pilot in command decided to perform a precautionary landing at the Radawiec airfield.
The investigation
The investigation, conducted by the operator's commission, focused on the malfunction of the FADEC system and the engine torque instability. Following the incident, the aircraft was prepared for flight by PZL service personnel. After verifying that the PRIMARY mode was functioning correctly, the helicopter was ferried on a technical flight to PZL Świdnik. The investigation involved consultations between the maintenance organization and the engine manufacturer. The investigation established that the failure originated within the engine's Electronic Engine Control Unit (EECU).
Findings
- The primary cause of the engine torque desynchronization was a malfunction of the engine EECU.
- The root cause was traced to the improper seating of mounting pins within the connectors by the operator, a result of discrepancies in assembly technology.
- The aircraft was temporarily removed from service until the faulty component was replaced and successful testing was completed.