What happened
On February 28, 2003, an SA 316B helicopter, registration I-BXWA, was performing a passenger transport flight from Stromboli to Lipari. The aircraft, operated by Air Walser on behalf of the Civil Protection, was carrying a pilot, a technician, and three passengers.
As the pilot approached a landing pad in the Acquacalda district of Lipari, he discovered that the tail rotor pedals were not responding correctly. Determining that the intended landing site was unsuitable for an emergency landing, the pilot diverted to a nearby beach. While the pilot could maintain directional control at higher forward speeds, the aircraft began to rotate around its vertical axis as the speed decreased for landing. The pilot successfully performed a water landing approximately one meter from the shoreline. All five occupants, who were wearing life jackets, evacuated the aircraft safely without injury.
The investigation
The ANSV examined the tail rotor drive shaft and transmission box. Technical inspections at a certified workshop revealed significant wear and deformation of the pitch control sprocket teeth on the tail rotor gearbox. Subsequent examination by the manufacturer revealed that the shaft had been incorrectly installed within the sprocket.
Investigators also found a mixture of oil and water inside the tail rotor gearbox; chemical analysis confirmed the water was seawater, introduced during the aircraft's immersion in the sea. Additionally, the investigation noted that the operator's technical logbook (QTB) was insufficient, as it only recorded basic flight data such as departure, destination, fuel, and weight, failing to provide necessary operational or maintenance details.
Findings
- Mechanical failure of the pitch control sprocket due to the deterioration of the engagement teeth and associated connecting components.
- Improper installation of the shaft within the sprocket during maintenance.
- Inadequate technical documentation provided by the operator's flight logbook model.
- The aircraft was operating in a capacity involving overflight of water without being equipped with emergency floats, contrary to applicable regulations.