What happened
On January 26, 2013, a Eurocopter AS355N, registration PR-HBE, was performing a passenger transport flight between a jungle clearing and the Ipixuna aerodrome in the state of Amazonas, Brazil. The flight, operated by Helibarra TáxiAéreo, was conducted under Visual Flight Rules (VFR) and lasted approximately 2 hours and 10 minutes.
During the final approach for landing, the pilot observed the illumination of the Master Caution light and a simultaneous drop in oil pressure in the number 2 engine. Upon touching down on the runway, the pilot detected the smell of smoke and immediately shut down both engines. The pilot and the passenger evacuated the aircraft without injury. However, a fire had broken out in the engine number 2 compartment, resulting in substantial damage to the engine.
The investigation
CENIPA, with the participation of the French investigation authority (BEA), conducted a technical analysis of the engine. The investigation team noted that the N2 turbine of the number 2 engine was locked, likely due to the fire. The engine was sent to the manufacturer's workshop in France for a detailed teardown.
Laboratory analysis of carbonized residues found in the combustion chamber revealed the presence of phosphorus, which indicated that lubricating oil had entered the air-fuel mixture. Further inspection of the engine's lubrication system identified a discrepancy in the double labyrinth seal. Investigators determined that impurities—specifically small dust particles—had accumulated in the front area of the labyrinth seal no. 7, obstructing calibrated air passages and allowing oil to leak into the combustion chamber.
Findings
- The primary cause of the fire was the presence of oil in the combustion chamber caused by a contaminated double labyrinth seal.
- The contamination was traced to dust particles entering through the air intake casing.
- Failure to follow manufacturer recommendations for frequent compressor washing in high-dust environments was a significant contributing factor.
- While the operator performed compressor washes every 30 hours as prescribed by the standard maintenance schedule, the manufacturer's manual recommended daily washes when operating in dusty or high-humidity environments, such as the jungle clearings used by the operator.
- Inadequate managerial supervision was identified as a contributing factor, as the company lacked sufficient oversight of maintenance services when operating away from its main headquarters.