On December 27, 2020, about 1520 eastern standard time, a Cessna 172C, N8311X, was substantially damaged when it was involved in an accident near Pleasant Valley, New York. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to the student pilot, after a normal preflight inspection she departed with 27 gallons of fuel and planned to remain in the traffic pattern to practice takeoffs and landings. On the downwind leg of the traffic pattern the tachometer indication dropped out of the normal operating range so she announced over the radio that she was experiencing an engine malfunction. She deployed partial flaps and turned the carburetor heat ON. Shortly thereafter, on final approach, the engine sputtered and lost all power. The student pilot performed the emergency checklist, cycled the magnetos, declared an emergency and performed a forced landing in a wooded area. The airplane came to rest inverted in swampy terrain amongst trees and sustained substantial damage to the wings and fuselage. The wreckage recovery was delayed about 8 months. During this time the propeller, instruments from the instrument panel, and the left yoke were taken from the airplane and not recovered. The last entry in the engine logbook stated all of the lower spark plugs were replaced due to “rough mag[neto] drop on run up” about 4 months before the accident. The airplane accumulated about 9 hours between the time the maintenance was performed and the accident. A postaccident examination was conducted during which the engine’s crankshaft was rotated by hand, and internal and valvetrain continuity was established. Examination of the cylinders with a lighted borescope revealed no anomalies. The cylinders and spark plugs contained dirt and debris from the swamp. The impulse coupling magnetos did not produce spark when turned by hand. The magnetos were removed and placed on a test bench; neither magneto produced a spark. Further examination of the magnetos revealed extensive corrosion present on the coil laminations. The left magneto had rust, debris, and corrosion present in the magneto and distributor gear housing; extensive rust was found around the coil laminations, housing, and the magnet. The right magneto had rust on the coil lamination and arcing throughout the distributor gear. The exterior housing of the magnetos was undamaged. The Champion Aerospace Magneto Maintenance and Overhaul Manual states the magneto time in service allowance is the Time Before Overhaul for the engine or 12 years. According to maintenance records, the engine was overhauled in 1984, 36 years prior to the accident. The right magneto was manufactured in 2006, the left magneto in 1997, 14 and 23 years respectively, before the accident.