Accident Overview
On May 13, 2015, at approximately 1845 central daylight time, a Robinson Helicopter R-44, registration N165RV, experienced a loss of engine power and struck terrain during an aerial application flight near Columbia, Illinois. The helicopter sustained substantial damage, while the commercial pilot was uninjured. Visual meteorological conditions prevailed, and no flight plan was filed for the Title 14 Code of Federal Regulations Part 137 local flight.
Pilot Report
The pilot reported that after making two to four passes over the field spraying, he heard the low rotor RPM horn and the engine "went silent." He estimated his altitude at 5 to 10 feet above ground level when the power loss occurred. The pilot lowered the collective and increased throttle, but the engine did not respond. He then reduced ground speed as much as possible and executed a run-on landing to the field. Upon touchdown, the right skid sank into the mud and wheat, causing a slight hop to the right, after which the main rotor struck the tail boom.
Examination Findings
On June 11, 2015, Federal Aviation Administration (FAA) inspectors supervised an examination of the helicopter at a maintenance facility in Cahokia, Illinois. The throttle, mixture, and fuel shutoff controls were checked and found to have normal freedom of movement with no anomalies. The oil filter was removed, cut open, and revealed no contaminants. A fuel sample from the fuel strainer assembly was blue and consistent with uncontaminated 100 low-lead aviation fuel. The fuel strainer bowl contents were filtered through a clean paper towel, showing no debris. The fuel filter showed no particulate contamination. The engine inlet air filter element had a sticky residue on its exterior side, but the element itself appeared clean and free of debris. Upon removal of the air filter, an unknown sticky substance was discovered coating the lower half of the throttle flap and the bottom half of the fuel injector body. The buildup was less than 1/32 inch at its thickest point, located at the base of the inlet portal. Despite the substance, the throttle flap rotated normally.
Fuel System Investigation
The refueling station used for the spray operation comprised a large storage tank on a trailer, equipped with a filtering unit and a supply hose. The hose, purchased from a farm supply store, bore a stamp indicating "farm fuel transfer hose w/static wire." The manufacturer's packaging identified it as a non-aviation refueling hose intended for gasoline, diesel, and oil. According to FAA Advisory Circular 150/5230-4B, the FAA has adopted standards from National Fire Protection Association (NFPA) 407, which specifies that refueling hoses conform to American Petroleum Institute (API) Standard 1529. It could not be determined whether the supply hose met API STD 1529 due to limited information. The FAA noted that the filter connecting the supply hose to the tank was discolored, though the aviation fuel in the tank appeared clear.
Two fuel samples were collected by the FAA: one from the supply hose and another from inside the tank. The hose sample was pale green, clear and bright with no water or particulate. The tank sample was light blue, clear and bright with no water or particulate. Typical 100 low-lead aviation fuel is light blue. Both samples were sent to an independent laboratory for testing. Results showed they were substantially identical, both having high unwashed gum content from different sources. The hose sample's unwashed gum content was nearly double that of the tank sample and appeared consistent with an additive used in plastics and rubber hoses. The tank sample's unwashed gum content was consistent with a stabilizing additive common in fuels.