What happened
On June 18, 2023, a Robinson R44 helicopter, registration LV-KBH, was conducting a recreational local flight departing from the "Don Osvaldo" heliport in San Carlos de Bolívar, Argentina. Approximately 20 minutes into the flight, while cruising at 350 feet, the pilot experienced intense vibrations and an audible alarm. Interpreting the situation as a potential loss of engine power, the pilot initiated an emergency autorotation into an unprepared field.
During the landing maneuver, the pilot was unable to control the rate of descent, leading to a hard impact with the ground. The impact caused the main rotor blades to strike the tail boom, resulting in the aircraft overturning. There were no fatalities among the four occupants, though the aircraft sustained significant damage, including the destruction of the main and tail rotors.
The investigation
The Argentine Transportation Safety Board (JST) examined the flight data recorded by the Engine Monitoring Unit (EMU) and the pilot's medical certification status. While the pilot believed the alarm indicated low rotor RPM, the EMU data revealed the opposite: a significant excess of rotor RPM, reaching 120% of the limit. The investigation also looked into the pilot's medical fitness, noting that the pilot's Class II medical certificate had been invalidated following a "Not Fit" result during a Class I medical examination.
Findings
- The pilot misidentified the emergency, as the EMU recorded high rotor RPM and engine RPM rather than the perceived loss of power.
- The high rotor RPM likely reduced the aerodynamic efficiency of the blades, contributing to the uncontrolled descent rate during the flare.
- The pilot was flying with an invalid medical certification, as the recent "Not Fit" rating for a higher-class medical had effectively revoked their existing lower-class authorization.
- There was no evidence that previous instances of exceeding engine parameters had been investigated by qualified technicians, as required by manufacturer manuals.