Piper PA-32-300 accident near Prescott Valley, Arizona, October 31, 2024

The NTSB's narrative final · quoted from the NTSB record

The pilot was conducting a local flight to try to replicate a fuel mixture leaning problem he experienced on the previous flight. The pilot experienced the leaning issues again and recognized unusual exhaust gas temperature (EGT) and fuel flow readings during the flight, so he elected to return to the airport. During the return to the airport the pilot heard two loud “booms” before the engine lost total power. Shortly after, smoke and flames appeared inside the cabin near the forward right floorboard. The pilot successfully extinguished the fire and performed a forced landing to an open field. The forward right area of the fuselage was substantially damaged. Examination of the engine revealed the No. 3 cylinder had separated from the engine case; the No. 3 connecting rod had fractured and mechanical damage was found to the engine case, camshaft, and crankshaft. Five of the eight No. 3 cylinder base nuts were not located. The examination revealed signs of fretting between both engine case halves, as well as on each of the six cylinder’s hold-down plates, consistent with a loss of torque of the engine case nuts and bolts and the cylinder base nuts. No other pre-impact anomalies were noted with the engine. Damage to the engine was consistent with the No. 3 cylinder base nuts losing their torque and the nuts coming off the studs, which enabled the cylinder barrel to come off the cylinder piston, resulting in mechanical damage to the studs, No. 3 connecting rod, engine case, camshaft, and crankshaft. The damage resulted in a fire originating in the engine compartment. Although the investigation did not determine why there was a loss of torque of the engine case nuts and bolts or the cylinder base nuts, the engine had operated about 72 hours since undergoing an annual inspection. FAA guidance for an annual inspection includes an inspection for visual evidence of excessive oil, fuel, or hydraulic leaks, and sources of such leaks, and directs inspection of engine studs and nuts for improper torquing. Accordingly, any improperly torqued engine studs or nuts should have been identified by the annual inspection.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.

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