What happened
On February 27, 2022, a Robinson R22 Beta helicopter, registration LV-KBQ, was performing a local pleasure flight near Canals, Córdoba. While the pilot was executing an approach for a practice landing in a field, the aircraft experienced a sudden increase in rotor speed. The pilot attempted to manage the situation by manually closing the throttle and initiating an autorotation after receiving clutch warnings. During the maneuver, low RPM alarms were also triggered. Upon contacting the ground, the aircraft rolled to the left, causing significant damage to the airframe, the main rotor, and the tail rotor.
The investigation
The investigation examined engine monitoring unit (EMU) data, aircraft wreckage, and manufacturer inspection reports. Analysis of the EMU data revealed that the rotor and engine speeds reached dangerous levels, specifically 132% and 133% RPM, respectively. The investigation also noted that the aircraft's tail boom sustained damage consistent with a strike from the main rotor blade, which caused the tail section to separate. Additionally, the investigation found that the transmission belts had shifted from their pulleys, though this was attributed to the impact with the ground rather than a pre-existing condition. The investigation was somewhat limited by the fact that the aircraft was moved from the site without authorization and the investigators were unable to access the private field where the accident occurred.
Findings
- The primary cause of the accident was a rotor overspeed reaching 132% RPM, likely triggered by a sudden reduction in collective pitch during the landing approach.
- This overspeed led to a loss of lift and an increased rate of descent, prompting a sharp maneuvering response from the pilot.
- The resulting flight dynamics caused the main rotor blade to strike the tail cone, severing the tail boom and damaging the vertical stabilizer and tail rotor.
- The pilot experienced a sequence of warnings, including high RPM indicators and clutch warnings, followed by low RPM audible and visual alarms during the descent.