Accident
A Hiller 1100 helicopter was destroyed by fire after executing a forced landing. The pilot reported that the exhaust gas temperature (EGT) had increased from approximately 700°C to 800°C, then rose further to 1100°C. Subsequently, the heat warning light illuminated. The pilot initiated a precautionary landing, during which the engine failed in the descent. The pilot then performed an autorotative landing without incident. After landing, a fire developed and could not be extinguished, resulting in the destruction of the aircraft.
Investigation
During the engine teardown, investigators observed that the first stage turbine wheel had extensive blade tip damage due to excessive temperature. The rotating wheels and stationary nozzles were badly damaged by either heat or foreign object damage (FOD), or a combination of both, except for the #1 nozzle, which remained in good condition. The various components appeared to have been assembled properly, with the exception of the #6 engine bearing seal, which was missing. It could not be determined whether the rope-type seal had been burnt away by the excessive temperature or if it had been omitted during assembly.