What happened
On November 30, 2020, a Bell 206L-4 helicopter, registration PR-HEB, was conducting a firefighting mission in the Parque Nacional do Pantanal Mato-Grossense, Poconé, Brazil. The aircraft, operated by IBAMA, was engaged in aerial firefighting using a helibucket to transport water.
During the operation, the aircraft experienced a sudden structural failure. The main rotor mast suffered significant damage due to a phenomenon known as mast bumping. This event led to the separation of the cabin roof and the main transmission gearbox from the fuselage. Additionally, the main rotor blades struck the tail boom, severing it into three distinct sections. The aircraft subsequently impacted a swampy area, resulting in the total destruction of the aircraft and the fatal injuries of the pilot.
The investigation
CENIPA's investigation focused on the mechanical failure and the operational environment. Investigators examined the wreckage and found that the damage to the main rotor mast was consistent with mast bumping, a condition characteristic of semi-rigid rotor systems under low load-factor flight conditions. The investigation also reviewed the pilot's training records and the operator's management of flight qualifications.
While the pilot held a valid commercial license and a single-engine turbine rating, there was no official record of a specific endorsement for the Bell 206L-4 model in the ANAC database. Furthermore, the investigation found no evidence of specific training for the pilot regarding external load or firefighting operations, which are required under Brazilian regulations.
Findings
- Mast bumping occurred due to inappropriate control inputs or environmental factors, likely induced by turbulence, wind gusts, or the dynamic interactions of the helibucket.
- Adverse meteorological conditions, including smoke, high temperatures, and strong turbulence, contributed to an unstable flight environment.
- There were systemic deficiencies in managerial oversight, as the pilot was performing specialized firefighting operations without documented type-specific endorsements or verified external load training.
- The helibucket was found to be structurally intact, suggesting it was likely jettisoned during the flight, though it is unknown if this was intentional or inadvertent.