Hillsboro, OR, USA
N152GB
CESSNA 152
While conducting takeoffs and landings during an instructional flight, the student pilot initiated a go-around. Shortly thereafter, the engine began to run rough and lost partial power. The instructor attempted to troubleshoot the engine, but was unable to restore engine power, and initiated a forced landing to a grass area beyond the end of the runway, during which the airplane nosed over. Examination of the engine revealed that the left magneto was producing spark randomly across its four posts. Internal examination of that magneto revealed that the distributor gear was intact; however, the copper electrode finger was found displaced from the plastic gear assembly. A service bulletin issued by the magneto manufacturer about three years before the accident stated that some units contained distributor gears that exhibited loose electrode fingers, the symptoms of which included "unusual RPM drop during magneto check, difficulty starting, and/or rough running engines." A separate service bulletin issued 38 years before the accident specified that the magnetos should be inspected internally every 500 hours. The operator reported that, at the time of the accident, the magneto had accumulated 402.7 hours since its most recent internal inspection. The operator further reported they conducted internal inspections of the magnetos every 750 hours. It is likely that the loose copper electrode finger resulted in the partial loss of engine power during the go-around.
On May 26, 2018, about 0935 Pacific daylight time, a Cessna 152 airplane, N152GB, sustained substantial damage when it was involved in an accident near Hillsboro, Oregon. The flight instructor and student pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The instructor reported that during their sixth stop-and-go landing, the student initiated a go-around. A short time later, the engine began to make a "plugging sound" and the instructor took control of the airplane. He adjusted the throttle, as the engine was "still making weird sounds," and informed the tower controller that the airplane was losing engine power. As the airplane neared the departure end of the runway, at an altitude of about 200 ft above ground level, the instructor initiated a forced landing. The airplane touched down in the grass area beyond the departure end of the runway and nosed over. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed substantial damage to both wings. The airplane was recovered to a secure location for further examination. The carburetor was replaced, and an external fuel source attached to facilitate an engine run. During the engine run, the engine lost power when the left magneto was selected. No additional evidence of any mechanical anomalies was observed, and the magnetos were removed for further examination. Examination of the left magneto revealed that when the drive shaft was rotated, spark was produced on each post in a random order. The magneto was disassembled and examined internally. The distributor gear was intact; however, the copper electrode finger was found displaced from the plastic gear assembly. The remainder of the internal components were unremarkable. The right magneto produced spark in firing order when the drive shaft was rotated by hand. The magneto was disassembled, and all internal parts were unremarkable. Slick Service Bulletin SB2-80C, issued in February 1980 and last revised in April 1991, specified that all 4300-series magnetos should be inspected externally every 100 hours, and internally every 500 hours. Slick Bulletin SB1-15A, originally published in July 2015 and revised in November 2018, outlined the potential for decreased service life of 4-cylinder magneto distributor gear assemblies, including the 4301 magneto. The service bulletin stated in part that, "…some of the returned products contained distributor gears exhibiting loosening of the electrode finger." In addition, the service bulletin stated that "…typical symptoms are unusual RPM drop during magneto check, difficulty starting, and/or rough running engines." Compliance with the service bulletin included replacement of the distributor gears equipped with a copper electrode. The operator reported that the left magneto was installed on the engine in June 2016, at a time since overhaul of 1,602.2 hours. At the time of the accident, the left magneto had a total time of 2,632.7 hours, and 402.7 hours since its most recent inspection. The operator further reported that they conducted internal inspections of the magnetos every 750 hours.
The partial loss of engine power during a go-around due to the loose copper electrode finger inside the left magneto.
Source: NTSB Aviation Accident Database
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