An Exploratory Study of General Aviation Aircraft Magneto Ignition System Failures

Abstract

This ex-post-facto, archival, single-case, research study explored early failures of magneto ignition systems in the training aircraft fleet operated by FIT Aviation, LLC (FITA). In 2012, an increasing number of early magneto failures prompted FITA to outsource the overhaul work to a specialty overhaul provider. Despite contracting out the overhauls, the early magneto failures continued to increase. Archival data, from the beginning of 2007 through the first quarter of 2017, came from engines logbooks associated with 48 Piper aircraft. Archival data were grouped into four categorical variables by aircraft type. A total of 518 magnetos, separately mounted as left or right magneto on each engine, provided two nominal variables, having a total of 313,000 individual magneto-operating hours logged during 157,850 flight hours. A benchmark of 600 service hours was used as the maximum service life of magnetos between overhauls. Magnetos with more than 600 service hours were excluded from the sample data as were magnetos removed when an engine was removed from the aircraft for overhaul or major repair. Of the remaining sample set (n=319), magneto replacements before 450 service hours were classified as early failures (n = 178). The mean time to failure for early failure was 250 hours. Analysis of variance (ANOVA) results indicated that aircraft type was not a factor. A lack of detailed information concerning magneto conditions at overhaul precluded this study from identifying specific factors behind the early failures. The conclusions were that it would be possible for the flight school to reduce the financial losses and schedule disruption impacts by lowering the magneto overhaul interval, reducing the risk of an in-flight magneto failure.