What happened
On May 10, 2017, an Enstrom 480B helicopter, registration N-480W, was conducting a cross-country flight under Visual Flight Rules (VFR) from Bolzano Airport to Linz. While en route, the aircraft suffered a catastrophic in-flight breakup. The incident began with the separation of one main rotor blade, which subsequently triggered the separation of the main rotor hub and the remaining two blades. During the flight, the helicopter caught fire and exploded. The aircraft followed a near-vertical parabolic trajectory before impacting the ground near Fundres, Italy. The impact caused a second explosion and damaged nearby power lines. The single occupant of the aircraft, the pilot, sustained fatal injuries.
The investigation
ANSV investigators conducted a site survey the following day, which included interviewing eyewitnesses and analyzing the distribution of wreckage. The debris field spanned approximately 20 and 500 meters, with one rotor blade found significantly distant from the primary wreckage. Investigators noted that the main rotor hub and two blades were located roughly 200 meters from the main crash site.
Technical examinations of the wreckage revealed that the main rotor hub assembly showed failures in the tension/torsion (T/T) straps of the blades that had separated. Laboratory analysis of the T/T straps using optical microscopy revealed that the first strap failed primarily due to tension, characterized by 45° fracture planes, while the second strap failed due to a combination of tension and torsion. Additionally, investigators examined a fractured dumper bolt and lug, noting a hammered fracture surface and evidence of corrosion. The investigation also involved coordination with the NTSB and the aircraft manufacturer to examine the gearbox and mast components.