Cessna T210N N5300A accident near Grayslake, Illinois

Probable cause

The failure of the No. 4 connecting rod due to inadequate oil lubrication for reasons that could not be determined because the postaccident engine examination did not reveal any anomalies that would have caused a lack of lubrication.

NTSB analysis

While en route on an instrument flight rules cross-country flight, the pilot noticed that the engine oil pressure had decreased; the oil pressure gauge was indicating in the yellow range, but the other engine instruments were showing normal indications. During the descent to landing, when the airplane was about 2,500 ft mean sea level, the pilot heard a "loud bang" from the engine, and smoke filled the cockpit. After declaring an emergency and requesting vectors from air traffic control to the nearest airport, the pilot executed an emergency landing just short of the runway in a wet, grassy area; the airplane slid, came to rest upright on the runway, and sustained substantial damage.

A postaccident examination of the engine revealed two large holes in the crankcase and mechanical damage on the inside of both crankcase halves. The No. 4 connecting rod, which exhibited thermal damage signatures, had separated from the crankshaft and thus punctured the holes in the crankcase. The No. 4 connecting rod bearings were significantly damaged consistent with lack of lubrication, and all of the connecting rod bearings displayed smear-type signatures consistent with lubrication distress. Gouging was found inside the oil pump consistent with the passage of hard particles during engine operation; it is likely that the metal pieces from the damaged engine passed through the oil pump and created the gouges.

The turbocharger's oil scavenge check valve spring was found broken, which resulted in the check valve not closing automatically; it would not restrict oil traveling from the turbo to the scavenge pump. The pilot reported a normal oil level before the flight and no signs of oil leaking. Further, according to the engine manufacturer, an open check valve would not have any effect on oil consumption during engine operation; thus, it was not a factor in this accident. The reason for the lack of lubrication could not be determined.

Text from the NTSB. Open the NTSB docket for CEN18LA031 for the full record.