Cessna T210F N6109R accident near Llano, California

Probable cause

A failure of the turbocharger that resulted in complete depletion of the engine oil and catastrophic internal failure of the engine. Contributing to the accident was improper and/or incomplete maintenance and inspection of the turbocharger.

NTSB analysis

The pilot had flown the airplane uneventfully on the outbound leg of a cross-country flight. On the return leg, the pilot noticed that he was unable to achieve full manifold pressure and that the engine was "running roughly." He stopped at an interim airport, where an aircraft mechanic examined the airplane but was unable to find any problems with the airplane or engine. The pilot subsequently departed to continue the trip home. While in cruise flight, he noticed that the oil pressure had dropped to 0 psi. The pilot retarded the throttle, declared an emergency with air traffic control, and diverted toward a nearby airport. The engine then lost total power. The airplane was unable to reach the diversion airport and sustained substantial damage to the fuselage during the forced landing.

Preliminary examination of the wreckage revealed that the engine was devoid of oil; no obvious leaks or other failures were apparent. Further examination of the engine revealed that the No. 1 connecting rod bearing and cap assembly had failed catastrophically due to oil starvation and that the liberated or partially liberated components caused significant internal damage to the engine. In addition, many internal engine components exhibited thermal distress signatures due to oil starvation. Detailed examination of the turbocharger revealed significant damage to the compressor and turbine blades, grossly excessive axial and radial freeplay of the compressor and turbine rotors, and fracture separation of the two rotors from one another. In addition, the turbocharger bearing housing, turbine outlet case, and turbine blades displayed coked oily/dirty residue. This evidence indicated that the engine oil was depleted by leaking and/or burning via the turbocharger.

The turbocharger manufacturer guidance specified certain inspections and that the turbocharger overhaul interval should coincide with, but not exceed, the time between overhaul (TBO) (hours in service) published by the engine manufacturer. The engine manufacturer's published TBO was 1,400 hours. However, the engine manufacturer guidance explicitly excluded engines with parts not supplied by the engine manufacturer, which was the case for this engine. The airplane maintenance records showed that the turbocharger was overhauled 13 years before the accident and had accumulated about 1,974 hours since that overhaul. The records did not document any relevant maintenance actions or inspections of the turbocharger since its overhaul. Given this information, it is likely that the turbocharger failure was the result of improper and/or incomplete maintenance and inspection. The turbocharger failure completely depleted the engine oil during the accident flight, and the oil depletion resulted in a catastrophic internal failure of the engine and a complete loss of engine power. There was insufficient evidence to determine when the oil depletion began or how long that process took.

Text from the NTSB. Open the NTSB docket for WPR17LA172 for the full record.