What happened
On July 13, 2018, a Yo-Yo series III helicopter, registration I-C881, was involved in a fatal accident near San Donà di Piave, Italy. The pilot was performing a repositioning flight at the Caposile airfield, moving the aircraft from a parking spot near the clubhouse to a hangar area.
Shortly after takeoff, the pilot lost control of the aircraft, which crashed into an agricultural field approximately 600 meters from the departure point. The impact was severe, resulting in the death of the pilot and the total destruction of the helicopter. Witnesses on the ground reported hearing unusually high engine noise and observing the aircraft's speed and altitude increase rapidly, accompanied by intense vibrations and the separation of components in flight.
The investigation
The ANSV investigation focused on the mechanical integrity of the aircraft and the operational procedures followed. Laboratory analysis of the wreckage revealed that the tail rotor drive shaft had failed due to excessive torsional load. Furthermore, the main rotor pitch control links showed evidence of failure due to the extreme forces experienced during the ground impact.
Investigators examined the aircraft's RPM governor system, which is designed to maintain constant engine RPM. Functional tests on the governor components—including the controller, motor assembly, and Hall effect sensors—confirmed that the system was working correctly. Data recovered from the aircraft's electronic flight instrument system (iEFIS) showed that the engine and rotor RPM had reached extreme levels, specifically 145% engine RPM and 148% rotor RPM, far exceeding the maximum allowable limits of 110%.
Findings
- The primary cause of the accident was the in-flight failure of the tail rotor drive shaft, triggered by an extreme engine overspeed.
- The pilot failed to engage the RPM governor prior to takeoff, leaving the engine unmanaged during a period of high power demand.
- The engine RPM levels were so high that the governor's operational range (80% to 115%) was insufficient to intervene and stabilize the engine.
- The Yo-Yo series III flight manual lacked critical safety information, specifically omitting the prohibition of takeoff with the governor in the OFF position and failing to mention the catastrophic structural risks associated with engine overspeed, which were documented in similar aircraft like the Robinson R22.
- The pilot's prior training history indicated a tendency to occasionally bypass pre-takeoff and post-landing checklists.