What happened
On August 24, 2000, an AS 355 N helicopter, registration PP-EMV, operated by the Goiás Military Police, was conducting a flight from Goiânia to perform an aerial survey of a bridge over the Corumbá River. Approximately ten minutes into the flight, the pilot noticed a significant temperature imbalance between the two engines, with a 50°C discrepancy in the T4 indicators.
In an attempt to equalize the temperatures, the pilot used the trim control button, a procedure not recommended by the manufacturer. Shortly after, the left engine experienced a loss of torque and gas generator (NG) rotation, accompanied by the activation of the metal chip light. Despite a suggestion from a passenger to return to the airport, the pilot continued the flight, even attempting to tap the instrument panel to unstick the indicator needle.
As the pilot attempted a forced landing near Teresópolis de Goiás, the left engine failed completely. In an attempt to manage the power, the pilot activated the "MAX POWER" button, which inadvertently restricted the available power from the remaining engine. The aircraft struck an elevation during the landing attempt and rolled onto its side, resulting in 3 light injuries among the six occupants. The aircraft sustained severe damage to the engine, main rotor, transmission, and tail rotor.
The investigation
CENIPA investigators examined the wreckage and the engines at the manufacturer's facilities in France. Testing of the No. 1 engine revealed that the gas generator turbine blades were uniformly burned and that the No. 4 bearing had melted due to insufficient oil flow and increased temperature. The investigation found that the oil flow to this bearing was only 50.5 l/h, which was below the required 65–100 l/h range. Additionally, a mispositioned internal component hindered proper lubrication.
The investigation also scrutinized the organizational culture of the operator. It was found that the flight activity was conducted empirically, lacking a systematic training program, standardized manuals, or formal evaluation of crew performance. The organization's structure was noted for being vulnerable to the influence of private interests and characterized by a lack of flight safety culture.
Findings
- Engine failure caused by the melting of the No. 4 bearing due to insufficient lubrication and high temperatures.
- Improper use of emergency procedures, specifically the pilot's attempt to equalize temperatures using the trim button and the failure to shut down the engine after the chip light activated.
- Incorrect application of power controls, where the pilot activated the "MAX POWER" button, reducing the power available from the functional engine.
- Deficient judgment and planning, as the pilot minimized the significance of the engine discrepancies and failed to execute a proper engine shutdown.
- Organizational deficiencies, including a lack of flight safety oversight, absence of standardized training programs, and a lack of formal operational manuals within the military police unit.