Cessna 177RG accident near Salinas, Puerto Rico, July 24, 2020

The NTSB's narrative final · quoted from the NTSB record

The pilot/owner and the instructor were conducting an instructional flight. The pilot reported finding no water contamination of the fuel during his preflight inspection of the airplane. They departed, performed airwork, and flew to an airport where several landings were performed. The flight then proceeded toward another airport, and during cruise flight at 1,100 ft mean sea level, the engine lost power. The pilot attempted to restore power but was unsuccessful. During the subsequent off-airport forced landing in soft terrain, the airplane nosed over during the landing roll. After the airplane was recovered, small amounts of water were found in samples taken from each fuel tank, the reservoir tank assembly, and the airframe fuel strainer. The fuel tanks were then drained and found to contain about 29 gallons of fuel; the drained fuel did not contain water or contaminants. Postaccident examination of the engine revealed severe contamination of the servo fuel injector inlet screen by ferrous material, as well as evidence of corrosion and water. Additionally, evidence of foreign debris contamination, water, and/or corrosion were found in the fuel strainer, the internal steel valves of the engine-driven fuel pump, and components of the fuel flow divider. No issues were otherwise noted with the engine powertrain, ignition, induction, or exhaust systems. During postaccident testing, leakage was noted from the right fuel cap. The most recent annual inspection was completed about 8 months before the accident. Following the first flight after the annual inspection, the pilot reported discrepancies to maintenance personnel regarding water in the fuel tanks, a rough running engine (which was later attributed to water ingestion), and a slow draining right fuel tank sump drain valve. The discrepancies were addressed by removing fuel tank sealant from the right-wing fuel tank drain valve boss ports and resealing the right inlet plate to the upper wing skin. According to the pilot, resealing the plate corrected the water intrusion issue. Given this information it is likely that the fuel system had been exposed to water for a period that was long enough for significant amounts of corrosion to develop. Ultimately, this resulted in the accumulation of corrosion and debris throughout the fuel system that most likely resulted in a blockage of the fuel injector inlet screen and/or fuel flow divider, fuel starvation, and the total loss of engine power during the accident flight. While the blockage of the servo fuel injector inlet screen occurred over time, it likely did not exist at the time of the airplane’s last annual inspection. The undetected blockage of the right wing fuel tank sump drain valve boss likely existed at the time of the last annual inspection, and may have contributed to the long-term water exposure and on-going water contamination issues after the annual inspection was completed.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.