LAX06TA284
LAX06TA284

On September 4, 2006, at 1550 Pacific daylight time, a Bell 212 twin-engine helicopter, N873HL, made an emergency landing at the Happy Camp Airport after the pilot received an engine fire warning in flight near Happy Camp, California. The helicopter sustained substantial heat damage. The Department of Agriculture (USDA), U.S. Forest Service (USFS) was utilizing the helicopter under contract as a public-use firefighting tool under the provisions of 14 CFR Part 133, external load operations. The helicopter was registered to Rogers Helicopters, Inc., Fresno, California. The commercial pilot, sole occupant and employed by Rogers Helicopters, Inc., was uninjured. Visual meteorological conditions prevailed and a USFS flight plan had been filed. The local flight departed at 1549.

According to initial accounts provided by the USFS, the helicopter departed Happy Camp airport with an external cargo load on a long line. Shortly after takeoff (about 30 to 45 seconds), the pilot smelled something burning. As the smell worsened, the pilot elected to return to the airport. In the cockpit, an engine fire warning light illuminated and the pilot observed smoke coming from the helicopter. He pulled the fire extinguisher handle on the number 2 engine and made a rapid descent to the airport. The pilot dropped the long line and landed without further incident. He shut down the engines, shut off the fuel valves, and exited the aircraft.

A post-landing examination of the helicopter revealed that the external surfaces of the Number 2 engine were covered in soot. A hole was observed on the gas generator case at the 5 o'clock position (aft looking forward). The hole appeared to be originating from the inside of the case towards the outside. The engine compartment and other accessories on the right side of the helicopter sustained damage.

Post accident disassembly and inspection was performed on the number 2 engine. During the teardown, investigators found foreign debris, consistent in appearance to a stator vane, lodged in a diffuser pipe. The diffuser pipe, which directs compressor discharge air to the combustion area, was located at approximately the 5 o'clock position (aft looking forward). Further inspection revealed a fractured stator vane in the compressor second stage stator assembly. Due to impact and heat damage to the stator vane fracture surface, the cause of cracking could not be determined.

Pratt & Whitney Canada investigators, in the presence of Federal Aviation Administration inspectors, concluded the following. The perforation of the gas generator case was most likely caused by a disturbance of compressed air flow from the diffuser pipes. The restriction in airflow caused by the lodged stator vane limited the flow of combustion liner cooling air, resulting in a localized increase in temperature and subsequent burning through combustion liner and the gas generator case.

The engine inspection revealed no other significant anomalies.

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