What happened
On October 3, 2016, a crew from the Torun Medical Air Rescue (LPR) was conducting training flights near Jeżów Sudecki. The mission involved practicing winch techniques with mountain rescue personnel (GOPR) and performing an Operational Proficiency Check (OPC). The flight included a simulated single-engine failure procedure, as permitted by the operator's instructions.
After completing winch training, the crew prepared the Eurocopter EC 135 P2+ for the engine failure simulation. The aircraft was positioned at a landing site east of Strużnica within the Jelenia Góra (EPJG) aerodrome control zone. During the simulation, the controlling pilot moved the right engine switch from the FLIGHT position to IDLE to mimic an engine failure.
As the simulation began, the helicopter entered a vertical descent, and the rotor RPM decreased. To arrest the increasing rate of descent, the trainee pilot increased the collective pitch and power to the maximum. This maneuver caused the torque (TRQ) to exceed limits on both engines, reaching 95.79% on the left engine and 96.334% on the right engine within 0.1 seconds. Once the rotor RPM dropped below 92%, the training mode deactivated, and the aircraft returned to twin-engine operation. The flight concluded without further incident.
The investigation
The investigation examined the flight parameters, the aircraft's weight and balance, and the environmental conditions. The aircraft's takeoff weight for the simulation phase was approximately 2700 kg, well within the maximum allowable limit of 2858 kg for those conditions. Following the event, the crew reported the torque exceedance to the LPR Safety Management Department and the manufacturer, Airbus Helicopters Deutschland. The aircraft was temporarily removed from service for a technical inspection, which was completed by maintenance personnel in Szczecine according to manufacturer guidelines. Following the inspection, the aircraft was returned to service.
Findings
- The torque limit exceedance was caused by the pilot's attempt to arrest a high vertical rate of descent by applying maximum power.
- An unfavorable wind direction (wind from the rear-left/left relative to the aircraft's longitudinal axis) contributed to the event.
- The high rate of vertical descent during the engine failure simulation acted as a contributing factor.