What happened
On August 2, 2011, a Bell 206B helicopter, registration PT-HCZ, departed from Heliponto Viganó I in Belo Horizonte, MG, bound for Aeródromo de Passa Tempo. The aircraft was carrying a pilot and three passengers. Approximately two minutes after takeoff, at an altitude of 500 feet, the engine failed. The pilot initiated an autorotation maneuver, but the aircraft performed a hard landing on a cleared lot being prepared for building construction. While the aircraft sustained substantial damage—including a punctured fuel tank, broken skids, and ventral damage—all four occupants escaped without injury.
The investigation
CENIPA investigators examined the engine, a Rolls-Royce Allison 2/C20J, and conducted laboratory testing on fuel samples. The engine was sent to Rolls-Royce in São Paulo, where a test bench evaluation revealed no mechanical anomalies or internal failures that could have caused the shutdown. However, spectrometric and FT-IR analysis of the fuel samples confirmed the presence of water in the fuel.
The investigation also looked into the maintenance and cleaning procedures at the helipad. It was discovered that prior to the flight, the aircraft had been washed using high-pressure machines, a practice specifically prohibited by the manufacturer's manual. Furthermore, the investigation found that the fuel filler cap's sealing O-ring was significantly degraded, and the cleaning staff lacked the technical qualification to perform such tasks safely.
Findings
- Fuel Contamination: The primary cause of the engine failure was the presence of water in the fuel lines, which prevented the engine from being restarted.
- Improper Maintenance Practices: The use of high-pressure washers for cleaning the aircraft, contrary to manufacturer recommendations, contributed to the incident.
- Inadequate Ground Support: The cleaning personnel were unqualified and performed tasks without following technical manuals or supervision.
- Maintenance Oversight: The degradation of the fuel cap's sealing O-ring was not addressed, partly because the maintenance manual at the time did not specifically require inspection of that component.
- Pilot Execution: The investigation noted that the pilot's control inputs during the autorotation may not have been sufficiently effective, potentially leading to the rotor RPM dropping below the 70% threshold recommended in the Rotorcraft Flight Manual.