What happened
On January 15, 2016, during a scheduled periodic maintenance inspection at SOT Szczecin, technicians identified structural issues on an EC 1s35 P2+ helicopter. The inspection, which included various periodic and supplementary tasks, focused on the rear section of the airframe. During the process, personnel discovered that a bracket for the fenestron control linkage had become loose. Additionally, a rivet connecting this bracket to the tail rotor drive shaft bearing support number 4 was found to be damaged.
The investigation
The investigation, conducted by the user's internal commission, established that the damage to the rivet head likely resulted from improper installation, specifically through incorrect riveting or the drilling of an oversized hole in the bracket. Due to ongoing structural vibrations, the rivet had loosened, leading to the enlargement of the hole in the bracket and causing the rivet to partially shear and deform.
Following the discovery, the engineering department documented the findings and contacted the manufacturer, Airbus Helicopters Deutschland, to determine the appropriate repair procedure. The manufacturer subsequently provided a Repair Design Approval Sheet (RDAS) on January 18, 2016. On February 8, 2016, technical personnel replaced the damaged bracket (P/N L535A1501216) with a new component. The helicopter was cleared for return to service on February 24, 2016.
Findings
- The primary cause of the incident was the loosening of the control bracket, which was most likely triggered by improper riveting techniques and exacerbated by aircraft vibrations.
- The damage was identified during a routine, planned maintenance program.