What happened
On March 4, 2000, an AS350BA helicopter, registration PT-YRI, operated by Riana Táxi Aéreo, was performing a flight from Santos Dumont Airport to Jacarepaguá Airport in Rio de Janeiro. While flying at approximately 400 feet near the Monumento dos Pracinhas, the pilot experienced a drop in rotor speed (NR) and a subsequent loss of engine power.
In response to the power loss, the pilot initiated an autorotation procedure, selecting an area used for model aircraft practice behind the Museum of Modern Art as an emergency landing site. During the final approach, the pilot encountered an unexpected utility pole in the flight path. In an attempt to maneuver around the obstacle, the pilot performed an abrupt and aggressive flare. This maneuver caused the tail boom to strike the ground and the main rotor blades to strike the tail boom, resulting in a heavy landing. The pilot emerged uninjured, but the aircraft sustained severe damage to the engine, main rotor, transmission, structure, and hydraulic systems.
The investigation
CENIPA investigators examined the engine and the fuel system following the discovery of a fuel leak near the engine's starter electrovalve. The engine was sent to Turbomeca representatives in Brazil and subsequently to the manufacturer in France for bench testing.
Testing revealed that the fuel leak at the electrovalve inlet was caused by significant deterioration of the threading on a T-junction. The investigation established that the threads of the union bolt had been stripped due to improper assembly. Specifically, insufficient engagement of the bolt during maintenance had created an overload on a limited number of threads, leading to plastic deformation and the eventual loss of the thread integrity.
Findings
- Inadequate maintenance: The primary cause of the engine failure was a faulty connection of a fuel hose at a T-junction within the starter electrovalve housing. The improper assembly led to thread deterioration and a subsequent fuel leak, which reduced fuel flow and caused the loss of power.
- Improper judgment: During the emergency landing, the pilot failed to adequately account for the presence of a utility pole in the chosen landing trajectory. The resulting evasive maneuver and aggressive flare significantly increased the rate of descent and led to the impact with the ground.