On June 18, 2021, about 1832 eastern daylight time, a Cessna 172N, N2797E, was substantially damaged when it was involved in an accident near Jupiter, Florida. The flight instructor sustained serious injuries and the student pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 instructional flight.
Due to his injuries, the instructor was unable to provide a statement. Attempts to contact the student pilot were unsuccessful. According to a Federal Aviation Administration (FAA) inspector, about 10 minutes after takeoff, at 2,700 ft mean sea level, the airplane experienced a total loss of engine power. The instructor was unable to restart the engine and attempted to land on a grass field; however, the airplane overflew the field and collided with a fence and trees before coming to rest nose-down in a creek. Review of automatic dependent surveillance – broadcast (ADS-B) data revealed that the airplane overflew several fields, ranging in length from approximately 1,500 ft to 2,500 ft, before the collision.
Examination of the wreckage by an FAA inspector and representative from the airframe manufacturer revealed oil streaks along the fuselage. Further examination revealed that the single-drive, dual output magneto had separated from the rear accessory section of the engine. The nuts, clamps, and lock washers that secured the magneto to the studs were not recovered and the studs did not exhibit any stripping or damage of the threads. Additionally, cuts in the magneto housing were consistent with the magneto vibrating over time, possibly due to tightening at an angle between the two studs.
Review of maintenance records revealed that the magneto was serviced on March 4, 2021, and the airplane’s most recent annual inspection was completed on May 17, 2021. The airplane had been operated about 215 hours and 74 hours since those dates, respectively. Additionally, a 100-hr inspection was performed on April 9, 2021.
The mechanic that serviced the magneto on March 4 stated that he did so as part of a pre-buy inspection. The mechanic had advised the seller that Airworthiness Directive (AD) 96-12-07 was superseded by AD 2005-12-06, which was not applicable to the model and serial number magneto; however, the mechanic was requested to perform the original AD anyway, to satisfy the buyer. The original AD was a 500-hr inspection of the magneto impulse couplings. The mechanic removed and reinstalled the magneto as part of the AD. The reinstallation included clamps and nuts that were used, but serviceable, and new lock washers. The mechanic added that there were no defects noted at the time of the inspection.
The mechanic who performed the subsequent annual inspection on May 17, 2021, stated that, when the magneto was previously removed and replaced, that mechanic (using a torque wrench) would tighten its two steel nuts and each nut has a star lock washer. The mechanic added that during the annual inspection he followed the CFR Part 43 checklist, which does not specifically include magnetos; however, he checked with his hand (by trying to wiggle all the accessories) that the magneto was secure. The Cessna checklist includes magnetos, but it is up to the operator to request that checklist be used, as it results in more labor during inspections and thus more cost for the inspection.