What happened
On September 18, 2017, during a scheduled maintenance inspection at the Warsaw-Babice Technical Service Station (SOT), a structural irregularity was discovered on an EC135 P2+ helicopter. The aircraft was undergoing a routine hangar inspection following 500 flight hours and 12 months of operation.
During a visual inspection of the main rotor blades, which were color-coded red, technicians identified a structural breach in the composite material of the blade attachment hole. Specifically, an irregular scratch was found on the edge of the mounting hole where the blade attaches to the rotor hub. The damage measured approximately 4 mm horizontally and 5 mm vertically along the edge of the bolt hole.
The investigation
Following the discovery, the damage was evaluated against the Aircraft Maintenance Manual (AMM) 62-11-00, 6-1. Under the criteria specified in the manual, the defect was classified as unallowable. The investigation team consulted with the manufacturer regarding the appropriate course of action. As a result of these consultations, the affected main rotor blade was sent to the manufacturer for further technical verification.
Findings
- The primary cause of the incident was a structural defect in the composite material, which was detected after 2,492 total flight hours during a scheduled maintenance check.
- The damage was located at the edge of the bolt hole used to secure the blade to the rotor hub.