Incident Involving an EC 135 P2+ Helicopter at Warsaw-Babice (SP-HXB)

Incident Overview and Investigation Details On June 7, 2016, an incident was recorded involving an EC 135 P2+ helicopter with the registration SP-HXB at the Warsaw-Babice airfield (SOT Warszawa-Babice). The event was classified as an incident by the State Commission for Aviation Accident Investigation (PKBWL), with the investigation supervised by Dariusz Frątczak and conducted by the user's commission. The investigation was completed on October 10, 2016. ## Technical Findings and Maintenance Actions During a scheduled hangar maintenance check following twelve months of operation, technicians inspected the main rotor shaft spacer tube for wear. In accordance with service bulletin SB EC135-64-023, they discovered a material loss measuring 6.6 x 5.7 x 1.02 mm on the inner race of the main rotor shaft roller bearing (P/N 0750118442) and abnormal wear on one of the spacer tube's (P/N 4649205015) protrusions. The incident was reported to the manufacturer, Airbus Helicopters (AHD), which recommended replacing all worn components and conducting a main gearbox inspection. On June 17, 2016, the damaged parts were replaced. During the subsequent main gearbox inspection, the missing fragment of the bearing's inner race was not found, as it was likely flushed out during an earlier oil change. Oil samples from previous changes showed no anomalies. After two gearbox flushes and checks of the oil filter and metal detector, the helicopter was cleared for continued operation. ## Probable Cause and Operational History The user's commission, in consultation with the manufacturer, determined that the damage most likely occurred during the installation of the bearing when the spacer tube was replaced, at a main gearbox flight time of 1511:06 FH. The gearbox operated with the damaged bearing for an estimated 833:19 FH, during which the damaged bearing race and the spacer tube tooth gradually wore down until the damage was detected at a total time since new (TSN) of 2344:25 FH. Throughout this period, all required scheduled inspections, oil changes, and oil sample analyses were performed regularly, with no deviations from standards detected.