What happened
On January 27, 2021, a Bell Helicopter Textron 212 was conducting a ferry flight from Pelarco to the Eulogio Sánchez Aerodrome. Approximately 40 minutes into the flight, while cruising at 1,600 feet over the Olivar commune, the aircraft experienced a sudden and significant drop in main rotor RPM.
Upon detecting the failure, the pilot initiated an emergency autorotation procedure. To avoid a populated area, the pilot directed the descent toward a cleared field. During the final stages of the descent, the pilot attempted an aerodynamic braking maneuver, known as a flare, at an altitude of approximately 40 meters. Because this maneuver was performed significantly higher than the recommended altitude, the rotor's kinetic energy was depleted before touchdown. This resulted in a high-energy impact with the terrain, causing the aircraft to bounce and spin, ultimately leaving the airframe heavily damaged and the pilot with serious injuries.
The investigation
DGAC Chile investigators examined the wreckage and the maintenance history of the aircraft. The investigation focused on the mechanical state of the Main Drive Shaft (MDS) and the execution of the emergency landing.
Technical analysis of the MDS, supported by findings from the Bell engineering laboratory, revealed that the front coupling of the shaft suffered from inadequate lubrication. This lack of grease led to excessive heat generation, which compromised the hardness of the gear teeth. The resulting wear caused the internal gears to decouple, breaking the power connection between the engines and the main transmission.
Investigators also reviewed the pilot's actions during the emergency. While the pilot correctly identified the failure and initiated the appropriate checklist, the timing of the flare maneuver was identified as a critical factor in the severity of the impact.