WPR20LA098

During the preflight inspection, the pilot conducted a visual fuel level check through the sight gauges in each wing. He determined that right wing had 7 gallons of fuel and the left wing had 6 gallons of fuel which he deemed was enough for a one-hour local flight. About 35 minutes after take-off, the engine started to "surge". The pilot manipulated the throttle lever several times, but there were no corresponding responses from the engine. The pilot elected to land on a nearby road; however, as he turned from base to final for the road, the engine "surged to life." The landing gear contacted the grass, and the airplane subsequently came to rest inverted. A postaccident examination of the airplane revealed an unmeasured amount of fuel in the right wing, and the left wing appeared to be empty. The gascolator drain valve was opened and no liquid was drained. Because the gascolator was located at the lowest point in the fuel system and contained no fluid, it is likely the engine was starved of fuel. An accumulation of dirt was noted on the fuselage lower belly skin (in the vicinity where a fuel drain tube exits the engine compartment), which was consistent with evidence of a previous fuel leak. Additionally, the area around the engine-driven fuel pump also exhibited evidence of a previous leak. The location of the potential leak could not be determined based on available information.

On March 4, 2020, at 1240 mountain standard time, a Flight Design CTLS airplane, N505MA, was substantially damaged when it was involved in an accident near Encino, New Mexico. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. During a preflight inspection, the pilot conducted a visual fuel level check through the sight gauges in each wing. He determined that right wing had 7 gallons of fuel and the left wing had 6 gallons of fuel which he deemed was enough for a one-hour local flight. About 35 minutes after take-off, the engine started to "surge." The pilot manipulated the throttle lever several times, but there were no corresponding responses from the engine. The pilot elected to land on a nearby road; however, as he turned from base to final for the road, the engine "surged to life." The landing gear contacted the grass, and the airplane subsequently came to rest inverted, substantially damaging the wings and the fuselage. A postaccident examination was conducted after the airplane was removed from the accident site. The engine remained attached to the airframe and all engine accessories remained attached to the engine via their respective mounts. The top spark plugs were removed and exhibited normal wear signatures. The engine crankshaft was rotated by hand using the propeller; rotational continuity was confirmed throughout the engine and valve train. Thumb compression and suction was also confirmed on all four cylinders. The engine-driven fuel pump was disassembled and the diaphragm appeared normal. However, the fuel pump vent/overflow hose nipple was missing the drain hose which is designed to be routed to a safe neutral air pressure area. Additionally, the area around the fuel pump had evidence of a previous leak. The gascolator drain valve was opened and no liquid was drained. Additionally, the gascolator housing was removed and the filter was missing. Both wings were removed during the recovery operation. The right wing contained an unmeasured amount of fuel and the left wing appeared to be empty. Low air pressure applied to the right wing fuel line fitting resulted in fuel expelled through the vent tube. Low air pressure applied to the left wing resulted in no fuel or air being expelled through the vent tube. Both wing fuel tank caps remained secure; no fuel samples were obtained from the right wing. Examination of the fuselage lower belly skin aft of the engine compartment found an accumulation of dirt in the vicinity of the fuel drain tube which exited the engine compartment in this area. A sample of the accumulated dirt was secured for further examination. The sample of dirt was examined at the NTSB Materials Laboratory using a Fourier Transform Infrared spectrometer to collect and process infrared wavelength absorbance spectra of the unknown material. A spectral library comparison search was performed on the residue spectrum which found spectral matchedto several clays. The search and the combination of spectral peaks indicate that the residue consisted mainly of soil. The presence of any hydrocarbons such as fuel or oil may have been masked by the strong spectrum of the soil present in the sample.