What happened
On April 3, 2018, at 09:06, a crew on duty for the Lotnicze Pogotowie Ratunkowe (HEMS) service departed from the Sokołów Podlaski base to respond to a medical emergency in Łuków. During the acceleration phase of the takeoff, at an altitude of approximately 700 feet, a FADEC MINOR warning appeared on the cockpit's CAD monitor, specifically indicating an issue with engine number 1. Although engine parameters remained within normal operating limits, the pilot decided to abort the mission and return to the Sokołów Podlaski base. The Eurocopter EC 135 P2+, registration SP-HXZ, landed safely back at the base at 09:13.
The investigation
Following the incident, a maintenance technician inspected the aircraft to identify the source of the warning. The investigation included resistance measurements performed on the P1 connector (pins "V" and "C") of the Power Turbine Speed Sensor (NPT), conducted in accordance with the engine maintenance manual (EMM). The technician discovered that when the engine was warm, the resistance measurements exceeded the maximum allowable limits specified in the technical instructions.
Findings
- The direct cause of the FADEC MINOR 1 warning was a faulty power turbine speed sensor.
- The sensor provided resistance readings outside of the permissible range during warm engine operations.