N6834RCessna T210G · 1966

On October 27, 2018, about 1045 Pacific daylight time, a Cessna T210G, N6834R, was substantially damaged when it was involved in an accident near Fillmore, California. The private pilot and pilot-rated passenger received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot stated that the airplane idled on the ground for about 15 minutes before departure while he performed a run-up and waited for traffic to vacate the runway. After making a normal departure, he continued east and climbed to about 4,000 ft mean sea level (msl). While in cruise flight with the airspeed about 105 kts, the engine suddenly lost total power. Despite his attempts to troubleshoot the failure, he could not restart the engine and performed a forced landing in a dry riverbed. After touchdown, the airplane rolled several hundred feet in the dry sand. The nose landing gear impacted a rock and collapsed, and the airplane nosed over and came to rest inverted.

An external examination of the engine revealed that the crankcase was intact with no evidence of pre-mishap catastrophic mechanical malfunction or fire. The crankshaft was rotated by turning the propeller blades that remained affixed to the crankshaft flange. 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. Upon rotation of the engine, the magnetos and their respective ignition harnesses produced spark in the proper firing order; the magneto impulse couplings were heard to release.

The upper sparkplugs were removed and examined. All sparkplugs were dark in color, but the engine manufacturer’s representative stated that they were consistent with normal wear. A lighted borescope was used to perform an internal examination of each cylinders’ combustion chamber, all of which displayed light combustion deposits.

Disassembly of the fuel manifold revealed a liquid that was brown in color and had an odor and appearance similar with a mixture of engine oil and aviation fuel. The engine-driven fuel pump dry-bay outlet pipe was removed, and a trace amount of oily film was present. Removal of the fuel injectors revealed that they were saturated with a brown liquid consistent in smell and appearance to engine oil.

The turbocharger compressor outlet pipe/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 electronic borescope was used to inspect the inlet tube. A yellow terry cloth towel (rag) was discovered blocking the turbo inlet tube and the towel had become entangled with the turbo charger compressor wheel. (see Figure 1.)

Figure 1: Turbocharger System (showing towel blocking inlet)

The compressor wheel was damaged, and several blades were distorted. After the towel was removed, the compressor wheel was free to rotate. When the turbocharger was unable to rotate normally, the ring seals which are used to seal the turbocharger shaft (between the compressor and turbine wheel) will allow oil to escape the shaft bearing area and enter the compressor section. If the airplane is inverted, the oil could migrate through the discharge duct to the upper deck pressure plumbing to the fuel injectors. From injectors the oil could build in the cylinders and, when inverted, drain into the fuel manifold. Additionally, with the induction tube blocked, no ram air would enter the cylinders. (see Figure 2.)

Figure 2: Turbocharger System (showing towel blocking inlet)

The oil filter displayed a date of June 8, 2018. The pilot stated that the airplane had accrued about 34 hours 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) in an effort to protect the turbocharger from foreign object damage.