ERA23LA162

About 15 minutes after takeoff during an instructional flight, the engine backfired several times and 5 to 10 seconds later the engine lost total power. The flight instructor assumed control of the airplane, maintained a 75-knot glide speed, and attempted to restart the engine, but without success. The flight instructor landed in a recently plowed field and, while at a slow groundspeed, the nose wheel settled into the mud and the airplane nosed over, resulting in substantial damage to the fuselage and both wings. The postaccident examination of the engine revealed that the single-drive dual magneto was not delivering power to the spark plugs. The examination of the magneto revealed that, while the left and right contact assemblies of the magneto were properly secured, neither of them opened during rotation of the rotating magnet assembly. Thus, with rotation of the magnet and the contact assembly points closed, the electrical path was shorting to ground, and not the normal path to the ignition leads, which likely resulted in the total loss of engine power. The left and right breaker cam followers, which would open each contact assembly after contacting a lobe of the breaker cam, was worn to less than the minimum specified for a new part and was insufficient to open the contact assembly points. Both cam followers exhibited accelerated wear and heat signatures consistent with lack of lubrication. Each felt pad, which provided lubrication to the oil-impregnated breaker cam, was dark and dry consistent with lack of lubrication. The magneto had operated satisfactory for nearly 40 years and 1,362 hours and then underwent a 500-hour inspection about 112 hours and 3 years before the accident, during which each cam follower was in satisfactory condition and displayed no abnormal wear. During that inspection the mechanic likely improperly cleaned the breaker cam and used incorrect oil to lubricate the felt of each cam follower. Thus, the improper servicing of the magneto likely resulted in the accelerated wear and heat signatures observed, both of which were consistent with lack of lubrication of each cam follower.

On March 23, 2023, about 1830 eastern daylight time, a Cessna 177B, N13612, was substantially damaged when it was involved in an accident near Travelers Rest, South Carolina. The flight instructor and private pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The pilot reported that about 15 minutes into the flight the engine “backfired a couple times” and 5 to 10 seconds later the engine lost total power, though the propeller continued to rotate. The flight instructor assumed control of the airplane, established a 75-knot glide speed, and attempted to restart the engine, but without success. The flight instructor reported that he chose a nearby field, notified air traffic control of his intention, and landed in the field. During the landing roll in the recently plowed field while at a slow groundspeed, the nose wheel settled into the mud and the airplane nosed over, resulting in substantial damage to the fuselage and both wings. The tachometer reading at the time of the accident was 1654.0. As a result of the nose over the owner reported warping of the fuselage and both wings, and a bent frame at the main landing gear. Postaccident examination of the engine revealed that the single-drive dual magneto did not produce spark at any of the spark plugs during rotation of the engine using the starter, when the magneto was rotated using a tool following removal from the engine, or when it was operated on a test bench at the manufacturer’s facility. Neither of the contact assemblies, which were properly secured, would open during hand rotation of the rotating magnet. Thus, with rotation of the magnet and the contact assembly points closed, the electrical path was shorting to ground, and not the normal path to the ignition leads. Disassembly inspection of the magneto revealed the left and right cam followers were worn about 0.022 inch and 0.020 inch less, respectively, than the minimum specification for a new part, which was insufficient to open the contact assembly points. The contact assembly gap when open was specified to be between 0.012 inch and 0.024 inch, with a median value of 0.018 inch. The examination revealed that both cam followers exhibited accelerated wear and heat signatures and both felts were blackened and dry. Review of the engine maintenance records revealed that a factory overhauled magneto was installed on December 31, 1979, at tachometer time 180. The magneto remained in service after installation until July 24, 2019, when at tachometer time 1,542.3, a 500-hour service was performed. According to the logbook entry, all parts were reused. The magneto remained in service from that date until the accident. The airplane’s last annual inspection was performed on December 12, 2022, at tachometer time 1635.0. The mechanic who performed the 500-hour inspection of the magneto reported that at the time of the inspection both cam followers were in satisfactory condition.He initially indicated that during the inspection he cleaned the oil impregnated breaker cam using electrical contact cleaner; but later indicated that he just wiped it using a clean cloth. As part of the magneto inspection, he lubricated each cam follower felt with a mixture of “STP” and heavy weight engine oil. He did notice a drift of the magneto to engine timing before the service, but he did not notice any drift of the magneto to engine timing during 2 subsequent annual inspections after the service was performed. The mechanic who performed the airplane’s last annual inspection reported he did not recall whether there was any drift of the magneto to engine timing. As part of the engine inspection, he did not remove the cover of the magneto or access any internal components of it. A review of the manual that the mechanic used to perform the 500-hour service of the magneto revealed that the oil impregnated breaker cam was specified to be cleaned using a clean, dry, lint-free cloth, and each cam follower felt was specified to be lubricated using 2 or 3 drops of 10-86527 lubricant (a high-temperature lubricant for breaker cams). Continental Aerospace Technologies (formerly Continental Motors, Inc.) Service Bulletin (SB) 643C, revised on July 21, 2017, specified that magnetos are electro-mechanical devices using rotating parts subjected to the same service treatment, environmental conditions, and wear as the engine. The SB also specified that magnetos older than June 1, 2015 (accident magneto) must be overhauled or replaced at the expiration of five years since the date of original manufacture or last overhaul, or four years since the magneto was placed in service, whichever occurs first, without regard to operating hours. Service bulletins are not mandatory for Part 91 operators.