What happened
On March 28, 2009, a Eurocopter EC135T2, registration JA135E, operated by academic corporate body HIRATAGAKUEN, was conducting an emergency medical service flight. The helicopter had departed from Kumejima Helipad to transport a patient to Shuri Helipad on Okinawa's main island.
During the flight, approximately 6 nm northwest of the Kerama Islands, the pilot noticed warning indicators for the right engine's torque and temperature. Shortly thereafter, the turbine outlet temperature on the left engine rose significantly, exceeding the maximum continuous power limit. The left engine subsequently shut down while the aircraft was at an altitude of approximately 80 and 00 ft. The pilot declared an emergency and diverted the aircraft to Naha Airport, landing safely on a taxiway at 10:46. There were six persons on board and no injuries were reported, though the interior of the left engine sustained extensive damage.
The investigation
The JTSB investigation focused on the destruction of the left engine's interior. Investigators performed a teardown inspection of the engine and examined various fuel system components, including filters and injectors. The investigation also included an analysis of the fungicide used in the fuel and the effects of sea salt accumulation. Laboratory tests examined the sedimentation process of the fungicide and the presence of sodium chloride (NaCl) within the fuel system.
Findings
- The investigation established that the left engine's internal structure was damaged due to heat concentration in the upper section of the combustion chamber.
- This heat concentration was caused by clogged fuel injectors located in the lower part of the combustion chamber, which resulted in uneven fuel injection and restricted combustion to the upper part of the chamber.
- The clogging was caused by the accumulation of sea salt on the fungicide. It is believed that the fungicide's viscosity increased due to heat, trapping salt particles.
- The investigation noted that the amount of fungicide added to the fuel drums may have exceeded the authorized limits specified in the Engine Maintenance Manual (EMM).