What happened
On March 14, 2018, a crew at the Olsztyn Air Ambulance (HEMS) base was preparing an EC 13lub5P2+ for hangar storage. The crew had attached a towing device, consisting of a transport trolley and landing gear wheels, to the aircraft's skids. While maneuvering the helicopter through the hangar door guides, the left rear landing gear strut fractured.
The structural failure caused the aircraft to tilt diagonally backward and to the left, resulting in the tail boom striking the ground. The crew immediately notified the Technical Coordination Center, and the aircraft was grounded.
The investigation
Technical personnel from the Maintenance Station (SOT) in Warsaw-Babice performed a detailed inspection of the aircraft. The examination revealed a fracture affecting three-quarters of the diameter of the left rear landing gear strut, along with damage to the left skid, the left rear boarding step, and the tail boom skid. Additionally, indentations were found on the left rear landing gear attachment and the fuselage skin at the attachment point. Damage was also noted on frame number 5 and the lightning arrester.
The manufacturer, Airbus Helicopters Germany (AHD), was notified and consulted. The damaged strut was sent to the AHD factory laboratory for forensic analysis. Following repairs, which included the installation of a complete new landing gear assembly and various structural repairs, the aircraft underwent extensive inspections of the hydraulic system, fenestron controls, and tail rotor drive components before being returned to service.
Findings
Investigation by AHD specialists identified that the improper anti-corrosion protection of the strut's internal cross-section was the probable cause of the fracture. Large surface areas were found to be lacking anti-corrosive coating. Furthermore, a previous repair to the paintwork had been performed incorrectly; the paint used did not meet technical specifications, which likely led to electrochemical corrosion in those areas.
Safety action
Immediately following the incident, the operator ordered a landing gear inspection for all EC 135 helicopters in the Air Ambulance (LPR) fleet. All operational and technical personnel within the organization were briefed on the event.