Accident Details
On October 27, 2018, at about 1045 Pacific daylight time, a Cessna T210G, registration N6834R, was substantially damaged when it was involved in an accident near Fillmore, California. The private pilot and a pilot-rated passenger sustained minor injuries. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
The pilot reported that before departure, the airplane idled on the ground for about 15 minutes while he performed a run-up and waited for traffic to vacate the runway. After a normal departure, he continued east and climbed to about 4,000 feet mean sea level (msl). While in cruise flight at an airspeed of about 105 knots, the engine suddenly lost total power. Despite troubleshooting attempts, the engine could not be restarted, and the pilot performed a forced landing in a dry riverbed. After touchdown, the airplane rolled several hundred feet in dry sand. The nose landing gear struck a rock and collapsed, causing the airplane to nose over and come to rest inverted.
Engine Examination
An external examination of the engine revealed the crankcase was intact with no evidence of pre-mishap catastrophic mechanical malfunction or fire. The crankshaft was rotated by turning the propeller blades, and thumb compression was established in all cylinders. Valve train continuity was observed with equal lift action at each rocker assembly; oil was found in the rocker box areas on all cylinders. When the engine was rotated, the magnetos and ignition harnesses produced spark in the proper firing order, and the magneto impulse couplings were heard to release.
The upper spark plugs were removed and examined; they were dark in color but consistent with normal wear per the engine manufacturer’s representative. A lighted borescope inspection of each cylinder’s combustion chamber showed light combustion deposits.
Findings
Disassembly of the fuel manifold revealed a brown liquid with an odor and appearance similar to a mixture of engine oil and aviation fuel. The engine-driven fuel pump dry-bay outlet pipe contained a trace amount of oily film. Removal of the fuel injectors showed they were saturated with a brown liquid consistent with engine oil.
The turbocharger compressor outlet pipe and hoses (discharge duct) were disassembled, and oil was present in the conduit. The rubber connector nearest the turbo compressor inlet was removed, and a lighted borescope inspection of the inlet tube revealed a yellow terry cloth towel (rag) blocking the turbo inlet tube. The towel was entangled with the turbocharger compressor wheel.
The compressor wheel was damaged, and several blades were distorted. After the towel was removed, the compressor wheel rotated freely. The report noted that if the turbocharger cannot rotate normally, the ring seals that seal the turbocharger shaft between the compressor and turbine wheel allow oil to escape from the shaft bearing area into the compressor section. If the airplane becomes inverted, the oil can migrate through the discharge duct to the upper deck pressure plumbing to the fuel injectors, then into the cylinders and drain into the fuel manifold. Additionally, a blocked induction tube prevents ram air from entering the cylinders.
The oil filter displayed a date of June 8, 2018, and the pilot reported about 34 hours of operation since the oil change. He stated that to access the oil filter, he removed the airbox and placed a towel in the scat tubing (not disconnected) to protect the turbocharger from foreign object damage.