Incident Description
On March 14, 2018, a HEMS crew at the Olsztyn base of the Polish Medical Air Rescue prepared an EC 135P2+ helicopter for removal from the hangar. After attaching a tug and a towing set consisting of a transport cart and wheels fixed to the helicopter skids, the towing began. While crossing the hangar door tracks, the left rear skid strut fractured. The helicopter leaned diagonally backward to the left, coming to rest on the tail boom. The crew notified the Technical Coordination Center duty officer. The helicopter was grounded from further flights.
Damage Assessment
Technical personnel from the Warsaw-Babice Maintenance Station inspected the helicopter and found:
- Fracture of the left rear skid strut through 3/4 of its diameter
- Damage to the left skid
- Damage to the left rear step
- Dent in the left rear skid attachment point
- Dent in the skin at the attachment point
- Damage to the tail boom skid
- Damage to frame No. 5
- Damage to the static discharge wick on the tail skid
Probable Cause
The manufacturer, Airbus Helicopters Deutschland (AHD), examined the fractured strut. Their specialist determined that the probable cause was inadequate anticorrosion protection of the strut interior; large areas were not covered with anticorrosion agents. Additionally, a previous repair of the paint coating had been performed contrary to procedures. The paint used did not meet technical requirements, which could have led to galvanic corrosion in the repaired areas.
Repairs and Inspections
After contacting AHD, the helicopter was transported by road to the Warsaw-Babice Maintenance Station. Inspections equivalent to those after a hard landing and after a landing with ground roll were performed. Necessary repairs were carried out per work order WO/HXK/015/2018 and RDAS-AIRF 103/2018. The entire landing gear was replaced, and damaged components were repaired. Subsequent inspections included:
- Visual inspection of the hydraulic system in the tail boom and fenestron area
- Inspection of the fenestron control system and tail rotor blade clearance
- Inspection of tail rotor drive components for cracks, deformation, damage, and corrosion
- Visual inspection of the tail rotor gearbox
- Visual inspection of the main rotor
- Inspection of the tail boom
- Inspection of the lower fuselage
After repairs and inspections, test flights were conducted with positive results. The helicopter was returned to service.
Corrective Actions
Following the incident, the operator ordered landing gear inspections on all EC135 helicopters in its fleet and briefed all operational and technical personnel on the event.