What happened
On August 10, 2006, a night flight was being conducted between the UNIBAN helipad and Congonhas Airport in São Paulo, Brazil. The pilot, operating an AS 350B2 with registration PT-YFB, noticed a momentary metal chip warning light shortly after takeoff. Approximately two minutes into the flight, the warning light became persistent.
In response to the engine warning, the pilot diverted the flight toward Campo de Marte Airport. During communications with the control tower, a low rotor RPM alarm sounded. Realizing that the aircraft could not reach the intended airport, the pilot initiated an emergency autorotation procedure, attempting to land in an area between two avenues. During the final flare, the pilot successfully avoided power lines but the main rotor struck tree branches. This impact caused a loss of control, resulting in the helicopter striking the ground with significant force. The impact caused a small fire, which was extinguished by bystanders using automotive fire extinguishers.
The investigation
CENIPA investigators examined the Arriel 1D1 engine to determine the cause of the power loss. The investigation involved the disassembly and analysis of various engine modules. While testing showed that the fuel control unit and lubrication systems met technical specifications, the oil filter contained a significant amount of metal particles.
Analysis of the engine modules revealed carbon deposits between internal couplers, suggesting improper assembly. Investigators also noted that the G3 bearing had deteriorated, leading to the engine failure. The investigation looked into the maintenance history, noting that the aircraft had undergone an annual inspection just two days prior to the accident. Evidence was also reviewed from maintenance facilities in Brazil to determine if maintenance errors or design flaws were responsible.
Findings
- The engine failure was caused by the deterioration of the G3 bearing.
- There were indications that the bearing failure may have resulted from improper assembly or maintenance procedures.
- Inadequate maintenance supervision at the maintenance facilities was identified as a contributing factor.
- The pilot was fully qualified and experienced for the flight conditions.
- The aircraft sustained severe damage, including destruction of the tail cone, rotor head, and blades, as well as structural deformation.