Accident Details
On July 9, 2023, at approximately 0947 central daylight time, a Robinson R-44 II helicopter, registration N163RK, was substantially damaged during an accident near Marble Falls, Texas. The pilot and two passengers were not injured. The helicopter was being operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight.
The pilot reported that he was conducting a power pole inspection flight with two non-pilot crewmembers. During the third day of the mission, while flying at about 250 feet above ground level (agl) and an indicated airspeed of about 50 knots, the engine experienced a total loss of power. The pilot entered an autorotation and turned right toward a suitable area for a forced landing. During the descent, he observed a set of power distribution lines crossing his path. He increased the collective control to clear the lines; after passing over them, he felt a slight shudder. The helicopter touched down on slightly sloped terrain, and during touchdown it rocked forward and aft. The lower vertical stabilizer contacted the ground, resulting in substantial damage. The pilot and crew exited the helicopter unassisted.
Investigation Findings
Examination of the helicopter revealed that both fuel tanks and the gascolator contained fuel along with a reddish-brown fluid that tested positive for water. A mechanic who performed postaccident maintenance reported that both fuel cells were coated on the inside with the red substance, and the electric fuel pump was clogged with it. The mechanic stated that the red substance could only be dissolved with a methyl ethyl ketone (MEK) equivalent cleaner. The fuel samples were sent to the NTSB Materials Laboratory for further examination.
Fuel Analysis
Further testing of the contaminated fuel samples indicated that the sample was consistent with a polyamide; however, a spectral library search did not find any strong matches to a single known substance. The pilot reported that he obtained fuel from several different airports as well as his own personal supply during the three-day mission. Postaccident testing revealed no contamination in any of the fuel delivery systems.