What happened
On March 11, 2022, a Bell Helicopter Textron 412 was conducting aerial firefighting operations in a rural area of Coelemu, Ñuble Region. The aircraft, equipped with a Bambi Bucket, had completed approximately fifteen water drops over the preceding hour without incident. During a subsequent refueling stop at an artificial lagoon, the pilot reported experiencing progressive vertical vibrations during the initial phase of takeoff. In response to these anomalies, the pilot released the water load and initiated a precautionary autorotation maneuver. This procedure resulted in a hard landing on the terrain, causing significant damage to the aircraft while the pilot remained unharmed.
The investigation — what DGAC Chile examined and established
The Directorate General of Civil Aviation (DGAC) conducted a thorough examination of the accident site, the aircraft wreckage, and maintenance records. Investigators verified that the helicopter and its external equipment did not strike any obstacles during the water loading process. Technical inspections were performed on the main rotor system, tail rotor, and flight control systems. Additionally, Bell Helicopter Textron’s engineering laboratory conducted static and dynamic tests on the isolation pylon mounts and friction dampers to identify potential mechanical sources of the reported vibrations. The investigation also reviewed the pilot’s qualifications, the operator’s maintenance compliance, and meteorological conditions at the time of the event.
Findings
The investigation established that the direct cause of the accident was abnormal contact with the ground during an autorotation maneuver. A key contributing factor was the unexplained vertical vibrations reported by the pilot, which could not be definitively attributed to a specific mechanical failure or external factor despite extensive testing. All aircraft systems, including the main drive shaft and rotor blades, were found to be within manufacturer specifications prior to the event. Meteorological conditions were suitable for visual flight rules, and no adverse weather factors contributed to the incident. The pilot held valid licenses and type ratings, and the operator was in full compliance with approved maintenance programs.
Safety action
DGAC Chile recommended that the Accident Prevention Department disseminate the findings of this investigation to relevant stakeholders. Specifically, it advised organizing a safety seminar for helicopter operators engaged in firefighting duties. This training should focus on the execution of autorotation maneuvers as an emergency response, analyzing the considerations and preventive measures required when encountering unexpected aircraft behavior during critical phases of flight.