ANC08LA004
ANC08LA004

On October 20, 2007, about 1218 Alaska daylight time, a Bell 206B helicopter, N345TV, sustained substantial damage during an emergency descent/landing, following a complete loss of engine power while hovering out of ground effect at Prudhoe Bay, Alaska. The helicopter was being operated by USA Airmobile, Fort Lauderdale, Florida, as a visual flight rules (VFR) local flight under Title 14, CFR Part 91, when the accident occurred. The commercial certificated pilot received serious injuries, and the boom operator received minor injuries. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The helicopter departed the Prudhoe Bay Airport about 0900 for a series of local utility maintenance flights.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on October 24, the pilot said the helicopter was contracted by the local power company to clean electrical power line insulators. He said the operation required the mounting of a 30-foot articulated spray boom on the right side of the helicopter, a 50-gallon water tank inside the helicopter, and a pressure pump on the left side of the helicopter. He said the equipment was installed on the helicopter pursuant to a supplemental type certificate (STC), and the equipment was operated by an onboard boom operator. According to the pilot, the helicopter was followed by a service truck, and landed every 7-8 minutes to top the helicopter's fuel tank up to 20-gallons, and refill the hot water storage tank. The pilot said the helicopter was hovering about 60 feet above the ground cleaning insulators, when without warning, the engine quit. He said he turned the helicopter away from the power lines, but because he had been carrying a lot of power and main rotor blade pitch, the helicopter descended rapidly, impacting the ground. The pilot stated that there were no known preimpact mechanical anomalies, and that the helicopter sustained substantial damage to the fuselage and rotor system during the impact with terrain.

The helicopter wreckage was taken to a facility in Wasilla, Alaska. An examination of the helicopter by the IIC began on December 11. The IIC was accompanied by representatives of the engine and airframe manufacturers and the operator. During the examination, it was found that both electric fuel boost pumps were clogged with a fibrous material. When power was applied, the aft pump would not pump any fuel, and the forward pump pumped fuel at a reduced rate. The electric fuel boost pumps were not needed for operating at the altitude where the helicopter was working, but they serve as the fuel conduit for the engine-driven fuel pump. Similar material was found in the airframe fuel filter. The engine was removed and shipped to the manufacturer for testing.

On March 5, 2008, under the supervision of an FAA inspector, the engine was connected to appropriate test equipment and run. According to the FAA inspector, the engine was started and run through a series of test settings. He said the engine ran without any mechanical problems.

On January 22, 2008, the wreckage was re-examined by the IIC. The fuel tank was cut open to expose areas not visible through factory openings. Adjacent to the forward electric fuel boost pump opening, the IIC found a triangular shaped, 4" piece of fibrous material. The material resembled an absorbent pad used to stop fuel spills.

The investigation revealed that the contract fuel provider routinely shoved the fuel nozzle through a hole in the plastic packaging of a bundle of absorbent pads, and into the edges of the pads, to keep from dripping fuel on the tundra. The fueling process was repeated every 7-8 minutes throughout the day.

Samples of the material taken from the fuel pumps, the piece found in the fuel tank, and an exemplar pad provided by the fuel contractor, were sent to an independent laboratory for testing. The tests revealed that all the samples were essentially identical.



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