What happened
On November 18, 2011, an ATR 72-212A, registration F-OIQO, operated by Air Tahiti, was undergoing engine startup at Moorea Aerodrome. During the startup sequence of the left engine, the flight crew observed that the inter-turbine temperature (ITT) failed to increase normally, stabilizing between 3/00 and 400 °C, while the engine rotation speed remained between 30% and 40%.
As the commander prepared to abort the startup, an engine fire alarm activated. The crew immediately implemented ground fire procedures. The first fire extinguisher discharge failed to suppress the flames, but the activation of the second extinguisher successfully extinguished the fire. There were no injuries or fatalities, and passengers were evacuated from the aircraft without incident. The left engine sustained minor damage.
The investigation
Investigators examined the engine and found traces of soot and burns, primarily on the ITT probe sheaths. The lower engine cowling also showed two areas of delamination with black marks. The investigation identified the origin of the fire as a fuel leak at the primary fitting of injector number 14.
Upon removal of the fitting, a cut O-ring was discovered. The investigation focused on the fuel injection system of the Pratt & Whitney PW120 series engine, which utilizes an annular combustion chamber with 14 injectors. While the system relies on metal-to-metal contact tightened to a specific torque, O-rings are used as a secondary seal. The investigation also reviewed maintenance practices, noting that the presence of these O-rings can sometimes mask improper torque during leak checks.
Findings
- The fire was caused by a fuel leak at the primary fitting of injector number 14.
- The leak resulted from inadequate maintenance, specifically an incorrect tightening of the injector fitting.
- The failure to achieve proper metal-to-metal sealing led to the leak once the O-ring deteriorated.
- The presence of the O-ring contributed to the incident by masking the improper torque during previous leak inspections.