Incident Details
On 15 January 2016, during planned hangar maintenance at SOT Szczecin, technicians examining an EC 135 P2+ helicopter discovered a loose fenestron control cable bracket and a damaged rivet connecting the bracket to the No. 4 bearing support of the tail rotor drive shaft. The maintenance tasks were carried out in accordance with work order WO/HXZ/052/2015 dated 29 December 2015, and included periodical inspection, 12 MO, Aerolite, Supplementary, Engines, and AD/SB inspections.
Findings
The damaged rivet head had likely failed due to improper riveting and/or an oversized hole for the rivet in the cable bracket. Subsequent structural vibrations caused the rivet to loosen, elongating the hole in the bracket and deforming the rivet, leading to partial shearing.
The maintenance engineer documented the finding and sent a report with photographs to the helicopter manufacturer, Airbus Helicopters Deutschland, for repair guidance.
Probable Cause
The loosening of the bracket was most likely caused by incorrect riveting and structural vibrations of the helicopter.
Actions Taken
On 18 January 2016, Airbus Helicopters Deutschland issued a Repair Design Approval Sheet (RDAS Nr AIRF 009/2016) specifying the repair procedure. On 8 February 2016, technical personnel replaced the damaged bracket (part number L535A1501216) with a new one. The maintenance tasks were recorded in task card No. 9/13 dated 8 February 2016. After completing the scheduled maintenance, the helicopter was cleared for return to service on 24 February 2016.
As a preventive action, the operator briefed technical and operational staff about the incident. No safety recommendations were issued by the Polish State Commission on Aircraft Accident Investigation (PKBWL).