On December 9, 2021, about 1544 Pacific standard time, a Cessna P210N, N152BT, was substantially damaged when it was involved in an accident near Hillsboro, Oregon. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the airplane had just been returned to service following its annual inspection when the accident occurred. He departed and turned northbound towards his destination airport, which was about 7 nautical miles (nm) away. The pilot stated that the airplane “struggled” to climb and at an altitude of about 1,100 ft agl the airplane began to lose altitude. He decided that the airplane wouldn’t reach the runway at the destination airport, so he turned back towards the departure airport for a precautionary landing. During this time, he verified that his magnetos, fuel, mixture, propeller, and throttle settings were in their correct positions. Shortly after, he saw spikes in the exhaust gas temperature (EGT) of three cylinders; he adjusted the mixture to try to cool the cylinders but the EGTs remained in the red arc. The pilot then initiated a precautionary landing in an orchard and the airplane came to rest upright between trees. The right and left horizontal stabilizers sustained substantial damage. A postaccident engine run was performed. When the right magneto was selected the engine ran up to 30 inches of manifold pressure and 2500-2600 rpm. When the left magneto was selected, the engine sound changed consistent with the engine shutting down. When both magnetos were selected, the engine ran up to 22 inches of manifold pressure and about 2200 rpm. When the magnetos were turned to the OFF position, the engine changed sound, consistent with the engine shutting down. The ignition harness was examined and the wires from the magneto to the ignition block revealed that the left magneto was set to the right switch terminal and the right magneto was set to the left switch terminal. Subsequently, both magnetos were removed and examined. The left magneto was unremarkable. The right magneto was found to have corrosion and green residue built up within the magneto. A chemical analysis of the residue revealed that the substance was primarily composed of copper and silicon (dirt), along with polyamide, which likely originated from the nylon gears. A review of the engine logbook revealed that the right magneto was last removed and serviced about 609 hours before the accident. Furthermore, the recommended Champion Aerospace 4300-6300 Series Magneto Maintenance and Overhaul Manual (500-hour overhaul) was last performed on the right magneto about 850.7 hours and the last overhaul was completed about 1389 hours (19 years) before the accident. According to the magneto manufacturer, corrosion is not an acceptable condition and corroded components should be cleaned or replaced as necessary. A postaccident examination of the airframe and engine revealed no additional mechanical anomalies or failures that would have precluded normal operation.