What happened
On September 25, 2017, at 13:23 local time, a crew consisting of a professional helicopter pilot was conducting an Operational Proficiency Check (OPC) near Andrzejówka. The flight was being performed in accordance with the established Operating Instructions. During the flight, the crew initiated a simulation of an engine failure during takeoff, specifically prior to reaching the Takeoff Decision Point (TDP).
During this simulated emergency procedure, the main rotor RPM dropped below 95%. This drop in rotor speed triggered the automatic disengagement of the training mode. Consequently, the torque (TRQ) on both engines exceeded permissible limits, with the left engine reaching 87% and the right engine reaching 86% within 01.125 seconds. Following the landing, the Technical Coordination Center (CKT) was notified, and the EC 135 P2+ was temporarily withdrawn from service.
The investigation
The investigation focused on the mechanical state of the aircraft and the environmental conditions at the time of the incident. Following the event, the Technical Service Station (SOT) in Szczecin conducted a thorough inspection of the helicopter in accordance with the relevant maintenance manual (MSM 05-51-00, 6-8) across categories A through D. The inspection revealed no mechanical irregularities or defects.
Findings
- The primary cause of the incident was a reduction in the vertical rate of descent speed.
- An unexpected change in meteorological conditions, specifically involving shifts in wind direction and wind strength, contributed to the event.