On November 1, 2018, about 1630 Alaska daylight time, a Piper PA-12 airplane, N3227M, sustained substantial damage during a forced landing, following a total loss of engine power about 8 miles northwest of Willow Airport (PAUO) near Willow, Alaska. The airplane was registered to and operated by the pilot as a 14 Code of Federal Regulations (CFR) Part 91 visual flight rules flight when the accident occurred. The commercial pilot sustained serious injuries. Visual meteorological conditions prevailed and no flight plan had been filed for the local area flight. The flight had departed a private airstrip located about 1 mile east of the accident location at about 1629. According to the pilot, during the initial climb, the engine popped three times "like a backfire", and then lost all power. He switched from operating on the left fuel tank to the right fuel tank and applied the carburetor heat, but the engine failed to respond. Subsequently, during the forced landing into trees, the airplane sustained substantial damage to the wings and fuselage. A friend of the pilot stated that this was the first flight following engine maintenance, where he, an airframe and powerplant mechanic, and the pilot had been troubleshooting for excessive magneto drops and a cold cylinder. He added that, they had just reinstalled the fine wire spark plugs after cleaning them. The National Transportation Safety Board (NTSB) investigator-in-charge, along with another NTSB investigator conducted a post-accident examination of the airplane following recovery. The spark plugs and rocker arm covers were removed from the engine and all spark plugs exhibited normal operational signatures with no defects or anomalies noted. The crankshaft was rotated by hand and thumb compression and suction were obtained on all four cylinders, and continuity was established throughout the engine and valvetrain. The wiring from the ignition switch to the magnetos was frayed and separated. It could not be determined if the separation happened before the accident or as a result of the accident. Both magnetos were removed from the engine and tested at Alaskan Aircraft Engines in Anchorage, Alaska. Both magnetos produced spark at all terminals as designed. Neither distributor was fractured, however the impulse coupler inside the left magneto was fractured but that did not preclude the magneto from sparking. The ignition harness was removed from the airplane and sent to Continental Motors for testing. The ignition switch was connected to a magneto synchronizer box (Model E50). The key was rotated through the OFF, L, R, and BOTH positions of the ignition switch with normal function observed.