What happened
On May 17, 2017, a crew operating from the Zielona Góra (EPZP) base initiated a Helicopter Emergency Medical Services (HEMS) flight to Trzebiatów. During the takeoff roll, the pilot observed a 20% difference in engine torque readings on the Full Authority Digital Engine Control (FADEC) Flight Limiter Indicator (FLI). Due to this discrepancy, the crew decided to abort the mission and perform a landing back at the departure airfield. The landing was completed without further incident.
The investigation
The investigation focused on the cause of the torque imbalance. Following the event, the aircraft was removed from service in accordance with instructions from the Technical Coordination Center. The pilot, accompanied by a mechanic, performed an adjustment of the engine turbocharger torques using the ENG TRIM switch. Following this adjustment, a ground run was conducted, which confirmed that the engine torque (TRQ) values were within the correct parameters according to the manufacturer's maintenance manual (MSM 05-62-00, 6-4). The EC 135 P2+ was subsequently returned to service.
Findings
- The probable cause of the incident was the unintentional movement of the ENG TRIM switch, located on the collective lever, which is responsible for maintaining engine turbocharger speeds.