What happened
On May 10, 2017, an Enstrom 480B helicopter, registration N480W, crashed in a rural area near Fundres, Italy, during a VFR transfer flight. The aircraft had departed from Bolzano airport for Linz, Austria, following a technical stop.
While navigating the valley, the aircraft began an irregular flight path. Eyewitnesses reported seeing parts detach from the helicopter followed by an explosion. The aircraft entered a ballistic descent, striking a medium-voltage power line before impacting the ground. The pilot, a 75-year-old experienced aviator, was killed in the crash. The impact and subsequent fire caused the total destruction of the airframe.
The investigation
The ANSV investigation focused on the structural integrity of the main rotor system. Investigators recovered the pilot's tablet, which revealed the flight path deviated from the original plan as the pilot attempted to gain altitude to clear mountain ranges.
Technical analysis of the wreckage revealed that the main rotor head and blades were found at a considerable distance from the primary impact site. Specifically, the investigators found that the hydraulic damper for blade number 1 had detached. This detachment triggered a chain reaction: the resulting vibrations caused the failure of the T-T straps, leading to the separation of blade number 2. The rotor head subsequently detached, and the third blade separated upon ground impact.
Findings
- The primary cause of the accident was the detachment of the hydraulic damper on the first main rotor blade.
- This failure was driven by the breakage of the bolt and lug connection due to corrosion on the lug.
- Chemical analysis showed a lack of cadmium plating within the threads of the lug, which allowed corrosive processes to develop.
- The maintenance personnel may have failed to recognize early signs of deterioration during the last inspection, potentially because the corrosion was hidden within the thread grooves.
- Storing the aircraft outdoors in a coastal environment likely accelerated the corrosion of the fastening hardware.