NTSB Factual Report

On May 13, 2015 about 1845 central daylight time, a Robinson Helicopter R-44, N165RV, impacted terrain following a loss of engine power during an aerial application flight near Columbia, Illinois. The helicopter was substantially damaged, and the commercial pilot was uninjured. Visual meteorological conditions prevailed at the time of the accident and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 137 local flight.

The pilot reported he had made 2-4 passes over the field with spray when he heard the Low Rotor RPM horn and the engine "went silent." He estimated he was approximately 5-10 feet above ground level (agl) when the loss of engine power occurred. The pilot lowered the collective and increased throttle but there was no reaction from the engine. He then slowed the helicopter's ground speed as much as possible and performed a run-on-landing to the field. The pilot reported that as the helicopter touched down the right skid sunk into the mud/wheat, which caused a "slight hop" to the right and the main rotor impacted the tail boom.

On June 11, 2015, Federal Aviation Administration (FAA) inspectors provided oversight of an examination of the helicopter at a maintenance facility in Cahokia, Illinois. The throttle, mixture and fuel shutoff controls were checked for correct freedom-of-movement and condition with no anomalies noted. The oil filter was removed, cut open and revealed no contaminants. A sample of fuel from the fuel strainer assembly revealed a blue colored liquid that was consistent with uncontaminated 100 low-lead aviation fuel. The contents of the fuel strainer bowl was poured through a clean white paper towel and no debris was observed. The fuel filter showed no signs of particulate contamination. The engine inlet air filter element exhibited a sticky residue on the exterior side of filter; however, the filter element looked clean and free of debris. Upon removal of the air filter, it was discovered that an unknown sticky substance coated the lower half of throttle flap and the bottom half of the fuel injector body. The buildup of residue was less than 1/32 inch at the thickest point, located at the base of the inlet portal. Despite the presence of the unknown sticky substance, the throttle flap was able to rotate normally.

The refueling station used for the spraying operation consisted of a large storage tank attached to a trailer. The tank was equipped with a filtering unit and supply hose. The supply hose was purchased from a farm supply store and contained a stamp on the exterior of the hose indicating "farm fuel transfer hose w/static wire." The supply hose was subsequently identified as an non-aviation refueling hose that was intended to dispense gasoline, diesel, and oil, according to the manufacturers packaging label. According to FAA Advisory Circular 150/5230-4B, "Aircraft Fuel Storage, Handling, Training, and Dispensing on Airports," the FAA has adopted standards used in National Fire Prevention Agency (NFPA) 407, Standard for Aircraft Fuel Servicing. NFPA 407 provides a standard for the storage and delivery of aviation fuel; it specified a refueling hose shall conform to American Petroleum Institute (API) Standard (STD) 1529. It could not be determined whether the supply hose connected to the re-fueling tank met API STD 1529 because of the limited information able to be collected on the hose. The FAA stated the filter connecting the supply hose to the re-fueling tank was discolored; however, the aviation fuel in the tank appeared clear.

Two fuel samples from the re-fueling tank were collected by the FAA, one sample obtained from the supply hose and another from inside the tank. The sample from the hose was pale green in color, clear and bright with no water or particulate observed. The sample from the tank was light blue in color, clear and bright with no water or particulate observed. Typical 100 low-lead aviation fuel is light blue in color. These two samples were sent to an independent laboratory for testing to evaluate the abnormal color of the fuel sample collected from the hose. Both samples collected were submitted to the laboratory in the same type of glass container. The test results determined the samples were substantially identical, with both having a high "unwashed gum" content appearing to be from different sources. The unwashed gum content in the hose sample was almost double that found in the tank sample and appeared consistent with an additive that is used in plastics and rubber hoses. The unwashed gum content in the tank was consistent with a stabilizing additive common in fuels.

NTSB Probable Cause

A total loss of engine power while maneuvering at low altitude for reasons that could not be determined during postaccident examination.