CEN24LA052

Maintenance personnel’s improper servicing of the magnetos, which resulted in their accelerated wear, failure, and the total loss of engine power.

About an hour after takeoff, during a personal flight, the engine suddenly lost total power. The pilot then made a turn toward the nearest airport to attempt to land; however, the airplane was unable to maintain sufficient altitude and the pilot elected to make a forced landing in a wooded area. The airplane impacted terrain and came to rest inverted, resulting in substantial damage to the fuselage, empennage, and both wings. The postaccident examination of the engine revealed that neither magneto delivered spark to the spark plugs. Laboratory examination of both magnetos identified arcing damage within their distributor assemblies. The arcing melted and carbonized the distributor block and distributor gear electrodes, resulting in an excessive electrode gap and a loss of electrical continuity, which prevented the magnetos from energizing the spark plugs and likely resulted in a total loss of engine power. The arcing damage was consistent with the presence of an insulating oil film on the distributor gear electrodes. The distributor block felt strips were saturated with oil, and oil droplets were observed on and around the felt material, consistent with oil migration from the felt strips to the electrodes. The felt strips were likely oiled improperly during the most recent magneto maintenance. Although the meteorological conditions at the time of the accident were conducive to carburetor icing, neither magneto produced spark during the postaccident examination. The pilot reported that the pretakeoff engine check was nominal. The magnetos had been in service for about 150 hours before the accident. Improper oiling of the felt strips during that maintenance likely led to the oil contamination and subsequent arcing observed in both magnetos.

On November 30, 2023, at 1513 central standard time, a Cessna 182C, N8880T, was substantially damaged when it was involved in an accident near Manitowoc, Wisconsin. The pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that after flying for about an hour, when the airplane was about 6 miles from the Manitowoc County airport (MTW) at an altitude of about 3,000 ft above ground level (agl), the engine lost total power. The pilot then made a turn toward MTW. The airplane was unable to maintain sufficient altitude, and the pilot elected to make a forced landing in a wooded area. The airplane impacted terrain and came to rest inverted. The airplane sustained substantial damage to the fuselage, empennage, and both wings. Postaccident examination of the engine revealed that neither magneto produced spark at any spark plug when the engine was rotated by hand using the propeller, or when the magnetos were rotated on a test bench after removal from the engine. Upon opening the left magneto housing, the left magneto exhibited signs of oily residue, carbonization, and arcing damage between the distributor gear electrode and the distributor block electrodes. The distributor block electrodes had melted and resolidified where they came into proximity with the gear electrode. Oil droplets were observed adhered to the felt strip that surrounded the distributor bushing. The rotor exhibited overload damage. Upon opening the right magneto housing, internal components also exhibited similar signs of oily residue, carbonization, and arcing damage between the distributor gear electrode and the distributor block electrodes. Regions of the distributor gear electrode were covered by a layer of carbonized material, and the distributor block electrodes had melted and resolidified where they came into proximity with the gear electrode. Oil droplets were observed adhered to the felt strip that surrounded the distributor bushing. The rotor exhibited overload damage consistent with impact forces. Continental Aerospace Technologies (formerly Continental Motors, Inc.) provided overhaul and assembly instructions for S-20-series magnetos in a Service Support Manual (Continental Motors, 2024). The manual specified that the felt strip surrounding the distributor bushing was installed dry in the groove adjacent to the distributor block bushing and cautioned against lubricating the felt strip with distributor block lubricant. A review of the engine maintenance records revealed that the overhauled engine was installed on October 23, 2021, at tachometer time 3,992.9 hours. The engine logbook entries did not mention installation of the magnetos; however, associated paperwork indicated that the installed magnetos were overhauled in November 2020. The airplane’s last annual inspection was performed on November 30, 2022, at a tachometer time of 4,081.5 hours. A review of the Carburetor Icing Probability Chart located in the Federal Aviation Administration’s Special Airworthiness Information Bulletin CE-09-35, Carburetor Icing Prevention, dated June 30, 2009, indicated that the atmospheric conditions in which the airplane was operating were conducive to the formation of serious icing at cruise power settings.