Cessna 172 N2797E accident near Jupiter, Florida

Probable cause

The flight instructor’s failure to obtain the proper touchdown point during a forced landing. Contributing to the accident was the improper service and subsequent inadequate inspection of the single-drive, dual magneto, which resulted in a total loss of engine power.

NTSB analysis

During a local instructional flight, about 2,700 ft above ground level, the engine lost total 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 flight track 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 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. Cuts in the magneto housing were consistent with the magneto vibrating over time, possibly due to tightening at an angle between the two studs. The magneto was removed and reinstalled as part of an inspection completed about 3 months (215 hours) before the accident. The mechanic who completed the inspection and reinstalled the magneto stated that 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.

An annual inspection of the airplane was completed about 1 month (74 flight hours) before the accident. The mechanic that completed the annual inspection stated he followed the Code of Federal Regulations 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.

Text from the NTSB. Open the NTSB docket for ERA21LA261 for the full record.