What happened
On February 10, 2020, a crew from the Wrocław branch of Lotnicze Pogotowie Ratunkowe was dispatched to attend to an accident on the A4 motorway near Nowa Wieś Wrocławska. The flight proceeded normally until the crew identified a landing site and prepared for a landing maneuver with a headwind component.
During the vertical descent, while maintaining a speed of approximately 20 knots at an altitude of roughly 30 feet, the EC 135-P2+ experienced a sudden loss of airspeed. The aircraft initially yawed to the right by approximately 45 degrees and drifted laterally. Although the pilot briefly stabilized the helicopter, the aircraft subsequently began rotating around its vertical axis to the right, completing approximately 1.5 turns while gaining altitude.
To prevent a collision with the ground or terrain obstacles, the pilot increased power by raising the main rotor collective to 70%. This action resulted in the torque limits for both engines being exceeded. Following the incident, the commander decided to abort the mission and return to the HEMS base at EPWR. The flight and subsequent landing were completed without further incident.
The investigation
The PKBWL examined the technical data following the exceedance of torque limits on both the left and right engine shafts (Category "F" exceedances). The investigation confirmed that the left shaft reached 96.5% for 2.875 seconds and the right shaft reached 95.8% for 2.750 seconds. Following the event, the aircraft was grounded for inspection. An aircraft mechanic performed a required inspection under the recommended maintenance category, and no irregularities were found, allowing the aircraft to return to service.
Findings
- The primary cause of the incident was the helicopter encountering a strong stream of turbulent air and its interaction with terrain obstacles, which led to Loss of Tail Rotor Effectiveness (LTE).
- The pilot's corrective action to avoid ground impact caused the engine torque limits to be exceeded.