On January 31, 2021, about 1144 Pacific standard time, a Cessna T182T airplane, N291FR, was substantially damaged when it was involved in an accident near Crescent City, California. The flight instructor and pilot rated student received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. During the flight, the flight instructor noticed a flashing red turbine inlet temperature (TIT) warning light. He enrichened the fuel mixture resulting in the TIT indication returning to normal. Shortly after, the engine began to run rough. The flight instructor switched to the left magneto and the engine lost power. He then switched to the right magneto and the engine continued to run rough. He switched back to both magnetos and the engine continued to run rough. The flight instructor then adjusted the mixture and turned on the auxiliary fuel pump. Despite his actions he was unable to get the engine to operate sufficiently to maintain altitude. The flight instructor located an open field and initiated a forced landing. The airplane landed in marshland and during the landing roll the airplane nosed over. Postaccident examination of the engine revealed that the magnetos would not produce a spark and had corrosion on their internal components. It was also noted that the pressurized magnetos did not have a moisture trap or filter installed. The magnetos were disassembled, and corrosion and rust were noted on the interior surfaces and interior components. The points were removed from the magnetos, and corrosion was noted on the contact surfaces. Sandpaper was used to remove the corrosion from both sets of points. Deformities such as deterioration and buildup of the contact surfaces were visible. The points were reinstalled on the magnetos and the magnetos were installed on the test bench. No spark was produced from either magneto. The magneto’s capacitors were bench tested and both failed under normal testing. An ohmmeter was used on the each of the (4) point assemblies and revealed inconsistent resistance on the surface areas (high points) of each point. A used set of points and capacitors were installed on the magnetos. The magnetos were installed on a bench and a normal amount of spark was observed. The used set of points had about 500 hours of operation during the test. The maintenance records revealed that, on February 1, 2019, at an airplane total time of 1,248.8 hours of operation, both magnetos were replaced with newly overhauled units. On November 10, 2020, the last annual was performed with an aircraft total time of 1,704.5 hours of operation. The accident occurred 82 hours of operation after the last annual inspection. At the time of the accident, the magnetos had 537 hours of operation since they were installed.