Pilot Debrief

PIPER PA-28-181 near Hollywood, FL — 2025-03-12

Final reportERA25LA141
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Date
2025-03-12
Location
Hollywood, FL, USA
Airport
HWO
Aircraft
PIPER PA-28-181
Registration
N3055B
Category
Airplane
Highest injury
Minor
Fatalities
0

Probable cause

A total loss of engine power was due to a fracture of the crankshaft at the No. 3 main journal, which originated from a preexisting, thermally induced crack that had gone undetected by maintenance personnel during an inspection performed as part of the engine’s most recent overhaul.

NTSB narrative

During the initial climb on an instructional flight, the airplane’s engine lost total power. The flight instructor then performed a forced, off-airport landing, during which the airplane impacted a tree, resulting in substantial damage to the right wing. Postaccident examination of the engine revealed that the crankshaft had fractured at the No. 3 main journal. Metallurgical analysis determined the fracture originated from a preexisting, thermally-induced crack at the aft side of the oil supply hole for the No. 3 connecting rod journal. A fatigue crack then initiated at the edge of the preexisting crack and propagated toward the No. 3 connecting rod journal, culminating in fracture of the crankshaft. The detailed metallurgical examination found that the features observed on the crankshaft showed evidence of three different fracture mechanisms associated with the crankshaft fracture. The region closest to the origin had intergranular features consistent with brittle overstress fracture. The next region showed evidence of mixed intergranular and transgranular features with dimple features consistent with ductile overstress fracture. The largest region showed features consistent with fatigue. It is likely that the final fracture region had features consistent with ductile overstress fracture, but the remaining overstress region was substantially obscured and obliterated by post-fracture contact damage. The intergranular region and part of the overstress region near the origin were oxidized, consistent with a different environmental exposure relative to the remainder of the overstress region and the fatigue region. Additionally, the bore of the No. 3 connecting rod oil supply hole was heat tinted in the area where the fracture surface was oxidized. This suggested that the No. 3 main journal likely experienced a high heat event, such as a bearing failure and/or inadequate lubrication. The high heat event then likely led to formation of the intergranular crack. Lead deposits consistent with the Babbitt layer on the interior surface of the main journal bearings were observed only in the intergranular region, including some deposits that ended precisely at the boundary. This suggested that Babbitt material migrated into the intergranular crack during the high heat event. While scoring and bearing damage was observed on the accident parts, the condition of the journals as found did not show evidence of a high heat event in the current installation. This indicated that the intergranular region likely formed during a previous period of service. Flakes and serrated chips of metallic debris were observed scattered throughout the intergranular and ductile overstress regions; however, similar debris was not observed in the fatigue region. The debris was consistent with material generated during journal grinding. Given the difference in oxidation across part of the overstress region and the presence of the debris across most of the overstress region, it is likely that the crack grew slightly during the grinding process, producing a comparatively short ductile overstress region. Once the cracked crankshaft was placed back in service, a fatigue crack initiated at the boundary of the ductile overstress crack. At the outer surface, the fatigue fracture intersected the ductile overstress crack behind the crack tip, further indicating that the fatigue crack was secondary to the overstress crack. The fatigue crack propagated aft along the oil supply hole for the No. 3 connecting rod journal and into the aft cheek until the remaining section could no longer support the load, resulting in fracture through the cheek at the aft end of the No 3. main journal. Review of the engine’s maintenance logbook showed that the engine was overhauled nearly 2 years before the accident and since that time, it had accumulated almost 2,400 flight hours. The maintenance records also indicated that the crankshaft was inspected by magnetic particle inspection during the last engine overhaul. The evidence observed on the crankshaft fracture surfaces indicated that the No. 3 main journal was likely cracked at the time of the inspection. The crack at the aft side of the oil supply hole for the No. 3 connecting rod journal likely had a total length of 0.147 inch at the No. 3 main journal surface at the time of inspection, which should have been detectable.

NTSB coding

Evidence available

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  • 7 docket documents
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Docket documents7

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