History of Flight
On July 31, 2017, about 1745 Pacific daylight time, a Cessna T210F airplane, N6109R, sustained substantial damage during a forced landing near Crystal Airport (46CN) in Llano, California. The private pilot and passenger were not injured. The airplane was registered to and operated by the pilot as a personal flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the cross-country flight that departed Modesto, California at 1530, destined for Hemet, California.
The pilot reported uneventful flight to northern California. On the return leg, he noticed he could not achieve full manifold pressure, and the engine was "running roughly." He stopped at an interim airport, where an aircraft mechanic examined the airplane but found no problems. The pilot and passenger departed to continue home. While in cruise, the pilot observed oil pressure drop to 0 psi. He retarded the throttle, declared an emergency with air traffic control, and diverted toward 46CN. The engine lost all power, and the pilot recognized the airplane would not reach the diversion airport, forcing a desert landing. At a low altitude, the pilot deemed the terrain suitable for a gear-down landing and selected the landing gear handle to the extended position. The airplane touched down while the landing gear was still in transit, coming to rest upright with deformed and collapsed landing gear.
Personnel Information
The pilot held a private pilot certificate with an airplane single-engine land rating. He reported a total flight experience of about 1,323 hours, including about 938 hours in the accident airplane make and model. His most recent flight review was completed in December 2015, and his most recent FAA third-class medical certificate was issued in August 2015.
Aircraft Information
The airplane was manufactured in 1965 and equipped with a Continental TSIO-520 series engine. The pilot purchased the airplane in spring 2011. According to the pilot, the airframe had a total time of about 3,534 hours, and the engine had about 1,974 hours. The most recent annual inspection was completed in July 2017. The airplane was equipped with a JPI EDM-700 engine monitor, which was sent to the NTSB Recorders Laboratory for data download.
Meteorological Information
The 1755 automated weather observation at Gray Butte Field Airport, Palmdale, California (about 8 miles northeast of the accident site) included wind from 020° at 10 knots, visibility 10 miles, scattered clouds at 16,000 feet, temperature 39°C, dew point 0°C, and an altimeter setting of 29.93 inches of mercury.
Wreckage and Impact Information
The touchdown location was flat, sparsely vegetated desert terrain. All three landing gear collapsed during touchdown. The lower cowl, fuselage underside, and fuselage aft of the cabin sustained crush, buckling, or scraping damage. The wings and empennage were undamaged, and the cockpit/cabin remained intact. Law enforcement and two FAA inspectors responded later that day. Inspectors reported sufficient fuel in the tanks for continued operation, but the engine oil sump was devoid of oil. Visual examination of the engine compartment and exterior revealed no significant oil leaks or venting, or pre-impact failures that could account for the oil loss. The pilot reported that the engine had just completed a top-overhaul about 11 hours prior, and oil quantity was checked and full before departure.
The airplane was recovered for detailed examination. The airframe and engine were examined by representatives of Continental Motors and the NTSB on August 9-10, 2017. The wings, vertical stabilizer, and elevator had been removed. The engine, propeller, and cowlings remained intact. External examination revealed oil/grease on some surfaces, consistent with normal in-service levels but not with a recent thorough cleaning. No oil was dripping from the fuselage, and recovery personnel stated there was no oil staining on the ground or on the recovery trailer. There was possible oil near the cooling air inlets, but the source was not obvious. No catastrophic engine failure or holes in the crankcase were observed. The source of oil stains was not positively determined but was below the No. 1 cylinder rocker assembly, which leaked oil when the rocker cover was removed, and near the turbocharger and oil filter. No separation failures or disconnections of lines were noted.
The electronic tachometer indicated 3,534 hours. The engine dataplate indicated model TSIO-520-C (overstamped with "C" and "M"), serial 140012-5-C. Continental Motors records show the engine was shipped new to Cessna in May 1965 as a TSIO-520C. The "C" overstamp denotes a field conversion; the "M" denotes the new model. The TSIO-520C is rated at 285 hp at 2700 rpm; the TSIO-520M is rated at 310 hp for takeoff, 285 hp continuous, and 230 hp cruise. The accident airplane's dataplate was not modified to show these changes. The airplane had "RAM T210" decals; RAM Aircraft is a known converter. A maintenance record entry from October 22, 2004 cited "Ram STC #SA2689SW" for an engine overhaul. RAM confirmed selling STC SA2689SW to N6109R in November 2004, which allows installation of the later 310 hp TSIO-520-M or R engine. A maintenance entry dated November 7, 2004 stated "installed new TSIO-520 engine serial no. 1400125C." An FAA Form 337 dated December 27, 2005 stated "Installed Teledyne Continental engine- TSIO – 520 – M, SN = 140012-5-C with RAM modification under STC# SA2689SW." The investigation was unable to determine why the 337 was dated a year after installation.
With all spark plugs installed, the engine rotated smoothly when the propeller was manually rotated, with less resistance than normal. Both magnetos remained intact, and impulse couplings snapped normally. Top spark plugs were inspected; all appeared to have normal wear with slightly dark coloration and fuel odor. The No. 1 cylinder top spark plug porcelain insulator was fracture-separated. Thumb compressions were achieved on all cylinders except No. 1. A borescope inspection showed the piston did not move in the cylinder; the exhaust valve was fixed open, and the intake valve fixed closed. Crankshaft continuity was confirmed. The No. 1 cylinder rocker box cover was removed; both rocker arms were intact. The exhaust valve rocker arm was depressing the valve, and spring tension was not relieved when the engine was rotated. The intake valve pushrod did not extend to the rocker arm, with about a ¾-inch gap. The cause was not determined by observation.
The three-blade constant speed propeller remained attached. All blades exhibited smooth rearward bending at about 2/3 span, consistent with ground contact with little or no power. No torsional twisting was observed. All blades rotated freely.
The engine was removed and shipped to Continental Motors in Mobile, Alabama for detailed examination.
Continental Motors Examination
The engine was stripped of external components. No significant non-impact anomalies were noted. All fuel system components were free of pre-impact damage or malfunctions. The external housing for the oil quantity indication rod had 3 segments of flexible tubing, whereas the manufacturer's part is a single-piece aluminum tube. The as-found assembly was about 15.5 inches long, compared to the design length of about 13.1 inches. This excess length would result in an erroneously low oil quantity reading. Continental representatives reported no known adverse effects of slightly overfilling the oil sump.
The oil filter was cut open and contained numerous metallic particles and fragments. The oil pump assembly was removed; it included scavenge and main pumps, both gear-type, intact, and rotating freely. No gears were damaged. The chamber walls of the main pump had significant rotational scoring, consistent with passage of small metallic particles harder than the aluminum walls.
No accessory gears were damaged. The oil sump was removed, and the case halves were separated. The lower cap for the No. 1 connecting rod was found separated in the oil sump, blackened and severely damaged. One cap bolt/nut assembly was found; the bolt was fractured in two, with severe elongation and necking. The No. 1 connecting rod remained attached to its piston pin and piston, moving freely. The crankcase bores for the two hydraulic lifters for the No. 1 cylinder were partially fractured, with liberated sections in the oil sump. The crankcase interior near the No. 1 connecting rod had gouges and scrapes, consistent with flailing of the failed connecting rod end. The crankshaft journal for the No. 1 connecting rod was blackened, scored, gouged, and peened; its bearing was not located. The oil sump contained significant metal flakes of black, brownish-copper, and silver-gray, consistent with remnants of the bearing. The other five connecting rods showed varying minor thermal distress; their bearings had varying wear and distress. The two aft cylinder skirts (No. 1 & No. 2) had impact and scoring damage, consistent with damage from liberated components. All pistons were intact.
All observed engine internal damage was consistent with oil starvation or exhaustion, but no obvious reasons for that condition were observed. There was insufficient evidence to determine the rate or duration of oil depletion. The cockpit instrumentation included an oil temperature gauge, but its pre-accident functionality and accuracy were not determined. Review of recorded engine oil temperature data from a separate system did not reveal abnormal behaviors that would have alerted the pilot.
Engine TBO Information
According to Continental Motors, for TSIO-520 C and M model engines, the time between overhaul (TBO) is 1,400 hours or 12 years, whichever occurs first. The manual states that Continental Motors does not provide a TBO for engines assembled with parts not supplied by Continental. The accident engine had all six cylinders replaced in April 2009 with Superior Air Parts cylinders, not supplied by Continental. Thus, the 1,400-hour/12-year TBO no longer applied.
Turbocharger Information
The turbocharger was mounted near the lower aft right side of the engine, above the area where the most oil was observed inside the cowling. Several compressor inlet blades were damaged. The compressor rotor rotated freely with about 1/8" axial and radial freeplay. After removal, turbine blades had similar damage, and the turbine rotor had about 1/4" axial and radial freeplay. The turbine rotor rotated independently of the compressor rotor, indicating a separation of their common shaft. The center housing near the shaft bearing and turbine blades displayed residue, some appearing to be coked oil or dirt affixed by oil. Oil lines were properly attached and intact with no evidence of leakage. The turbocharger was partially disassembled; the shaft was confirmed fractured at the turbine wheel end. Silvery metal fragments were observed near the shaft bearing area, and the turbine wheel shroud was cracked.
The turbocharger dataplate indicated it was designed by Garrett AiResearch and "Factory Rebuilt." Garrett was subsequently acquired by Honeywell, which sold some lines to Kelly Aerospace, which was purchased by Hartzell Engine Technologies (HET) in 2010. HET did not take on liability for all previously manufactured units; those remained with Kelly Aerospace, which has since declared bankruptcy. Maintenance records indicated an overhauled turbocharger was installed in October 2004 by Corona Cylinder and Engine Overhaul Inc. No further turbocharger maintenance or inspection actions were documented, except wastegate servicing. The turbocharger accumulated about 1,974 hours over about 13 years, with no dedicated inspections. HET guidance recommends visual inspections concurrent with periodic engine inspections and specifies a TBO coinciding with the engine TBO but not exceeding 12 years. However, operation under Part 91 does not mandate compliance with these intervals.
Additional Information
The JPI EDM-700 engine monitor data was successfully downloaded. Recorded parameters included EGT, CHT, oil temperature, outside air temperature, battery voltage, and time. The accident flight was the last of 17 power cycles between July 13 and July 31, 2017, with a duration of about 2.1 hours. For most of the accident flight, oil temperature stabilized at about 200°F. About 55 minutes before data end, oil temperature gradually decreased to about 120°F over 15 minutes. The trace became spiky about 10 minutes later, with temperature between 120° and 135°F. About 5 minutes before data end, EGT and CHT decreased rapidly, consistent with significant power reduction. About 1 minute before data end, oil temperature began to rise, peaking at about 140°F at data end.