WPR16LA020

The commercial pilot of the helicopter reported that, after he released the external load of trees in the loading zone and about 50 ft above ground level, it seemed like the engine experienced a partial loss of power. The pilot stated that he heard an abnormal noise as the helicopter began to spin to the right, and the low rotor rpm warning light illuminated. The pilot jettisoned the external load line and rolled the throttle toward a closed position in order to counteract the yawing motion, with no response noted. The pilot then initiated an autorotation; during the landing sequence, the helicopter impacted a tree and came to rest upright in a nose-high position. The pilot further stated that, after the helicopter came to rest, he noted that the engine was at a "very slow idle" and he had to shut down the engine. Postaccident examination of the helicopter revealed no evidence of any preexisting mechanical anomalies that would have precluded normal operation. The engine was removed and installed in an engine test cell and ran throughout various power settings. The airframe fuel filter was removed. The filter element was almost black. The fuel removed was dark, and debris was observed within the fuel filter bowl. The fuel sample from the filter housing was tested and found to be within Jet A specifications. The debris noted within the sample contained various metals, the source of which could not be determined. Given that fuel was found throughout the fuel system, it is unlikely that the debris in the filter resulted in a blockage and restriction of fuel flow; however, the reason for the partial loss of engine power could not be determined.

On November 2, 2015, about 1424 Pacific standard time, a Bell 206B, N22743, was substantially damaged during an autorotation landing following a partial loss of engine power near Dallas, Oregon. The helicopter was registered to and operated by Applebee Aviation under the provisions of 14 Code of Federal Regulations Part 133. The commercial pilot, sole occupant of the helicopter, sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the external load flight. The local flight originated from a staging area about 15 minutes prior to the accident. The pilot reported that prior to the accident flight; the helicopter was refueled with 30 gallons of Jet-A fuel. The pilot departed from a staging area and began lifting Christmas trees from a field to a nearby loading zone. The pilot stated that after about 5 or 10 loads, he released a load of trees in the loading zone and shortly after, it seemed like the engine went to a reduced power setting at an altitude of about 50 feet above ground level. He further stated that he heard an abnormal noise originate from the helicopter as the helicopter began to spin to the right along with an illumination of a low rotor RPM light. The pilot jettisoned the external load line and rolled the throttle towards a closed position in order to counteract the yawing motion, with no response noted. The pilot initiated an autorotation and during the landing sequence, the helicopter impacted a tree. Subsequently, the helicopter came to rest upright in a nose high position. The pilot further stated that after the helicopter came to rest, he noted that the engine was at a "very slow idle" and he had to shut off the engine. Postaccident examination of the helicopter by a Federal Aviation Administration inspector revealed that the tailboom forward of the tailrotor gearbox was twisted about 90o. The helicopter was recovered to a secure location for further examination. On December 2, 2015, the recovered helicopter was examined at the facilities of AvTech Inc., Auburn, Washington, by the National Transportation Safety Board (NTSB) investigator-in-charge and representatives from Rolls Royce and Bell Helicopters. The examination revealed that the skids were removed to facilitate wreckage transport. Flight control continuity was established throughout the airframe to the main rotor head and aft to the tailrotor. An area of impact damage was observed just forward of the tailrotor gearbox. Continuity of the engine controls was established from the cockpit controls to the engine. The airframe fuel filter was removed. The filter element was dark, almost black in color. The fuel removed was dark in color (charcoal looking). Debris was observed within the fuel filter bowl. Samples of the debris and fuel were retained. Power was applied to the helicopter, and the fuel boost pumps were turned on. Fuel expelled out of the engine supply fuel lines. A sample was taken, and the fuel appeared to befairly clear in color with no debris noted. Visual inspection of the fuel tanks revealed that about 10 to 20 gallons of fuel was present. The engine was visually intact and all fuel and air lines appeared to be secure. N1 and N2 rotated freely and continuity was established throughout the engine to the gearbox. The engine fuel filter was removed from its housing, and a fuel sample was collected. The fuel was dark in color and contained an unknown sediment inside. The filter was dark in color. The fuel from the fuel nozzle supply line was captured and was found clear in color. The engine was removed and subsequently shipped to Rolls Royce for further inspection. Fuel samples were retained and sent for subsequent testing. On April 6, 2016, the engine was further examined at the facilities of Rolls Royce, Indianapolis, Indiana. The engine was placed on an engine stand, and visually examined. Compressed air was applied to the port where the PC Line connects to the compressor scroll. Air was found leaking from the PC line that connects to the fuel control unit. The engine was subsequently installed in an engine test cell and run for about 90 minutes throughout various power settings. During a governor droop test, when the load was removed from the engine to test the governor's ability to maintain RPM, N2 RPM increased to the limit for the test cell. Throughout the engine run, the engine produced rated power at cruise flight and takeoff power settings. The power turbine governor and fuel control unit were removed and subsequently examined at the facilities of Honeywell, Inc., South Bend, Indiana, under the supervision of an NTSB investigator. The investigator reported that the bench tests of the power turbine governor revealed the unit was "sluggish" however, would not result in a loss of engine power. The fuel control unit was placed on a test bench and functioned normally. The fuel sample from the fuel filter housing from the accident helicopter was submitted to a third-party laboratory for analysis. There was a small amount of unknown debris visible in the sample. Three tests, including Freezing Point; Flashpoint and Distillation were performed on the fuel sample. All tests were found to be within specification for Jet A fuel. The debris was retained and sent to the NTSB Materials Laboratory for further examination. The testing results for the debris found higher elemental levels of calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), nickel (Ni), potassium (K), silver (Ag) and zinc (Zn). The source of the debris could not be determined.