On October 21, 2020, about 1150 Pacific daylight time, an experimental, amateur-built, Glasair III airplane, N1YX, was substantially damaged when it was involved in an accident near Hayward, California. The pilot sustained serious injuries. The airplane was being operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that on the day of the accident, he was going to return the airplane to the owner in Oregon. He added 15 gallons of fuel to the fuel tank and believed that 15 gallons of fuel were already in the tank. He reported that the takeoff was smooth and normal, but the engine soon lost all power. He didn’t change the fuel switch position as “it was always in both.” He then made a forced landing on a golf course, where the airplane struck two trees. Multiple witnesses reported hearing the engine making popping noises after the pilot started the engine. One reported hearing a deep thumping sound before the takeoff, and another reported hearing popping and observing black smoke trailing from the airplane after the takeoff. According to a mechanic, who had known the pilot for several years, he had done some work on the airplane. He replaced the propeller but did not finish the work, due to other priorities. Later, when he looked at the airplane, someone had completed the work. He did not know who completed the work, but he did know that the pilot was not an A & P mechanic. A postaccident examination of the wreckage revealed the fuel filter cartridge was clogged with corrosion and the fuel filter bypass was rendered inoperative from the corrosion (see figure 1). The maintenance logbooks were not available for examination, and therefore the historical data for the fuel filter was not determined during the investigation. Figure 1. Fuel filter cartridge and housing. The pilot did not submit the Pilot/Operator Aircraft Accident/Incident Report Form 6120.1.