History of Flight
On September 28, 2021, at approximately 1608 eastern daylight time, a Cessna T210N (registration N1925U) was substantially damaged during a forced landing near East Sparta, Ohio. The pilot, the sole occupant, was not injured. The flight was operated under Title 14 Code of Federal Regulations Part 91 as a personal flight.
According to automatic dependent surveillance-broadcast (ADS-B) data, the airplane departed from runway 2 at Wadsworth Municipal Airport (3G3), Wadsworth, Ohio, about 1534. It flew about 2.8 miles north of the airport, then entered a climbing turn to the south, leveling at 3,500 ft mean sea level. At 1555:12, it turned left to the southeast.
The pilot reported that during cruise flight, the engine began running rough with a sudden decrease in exhaust gas temperature (EGT) for cylinders Nos. 2 and 4. He contacted Cleveland approach, declared an emergency, and turned left toward Akron-Canton Regional Airport (CAK). Engine monitor data showed that at 1604:54, the engine ran erratically with a sudden decrease in manifold pressure and EGT for cylinders Nos. 2 and 4. The engine continued with partial power for about 100 seconds before losing total power.
ADS-B data indicated that after the power loss, the airplane descended from 3,500 ft msl and decelerated from 130 to 79 knots calibrated airspeed. The last ADS-B return at 1608:05 showed the airplane about 240 ft west of the accident site at about 163 ft above ground level. The pilot chose to force-land in a hilly pasture. The ground track and descent profile were consistent with a landing on an east-southeast heading. The pilot reported that the nose gear separated during the landing roll and the airplane came to rest nose down.
Aircraft and Engine Information
The airplane was equipped with a Continental TSIO-520-R engine (serial No. 1032649), manufactured on July 18, 2016, and installed new on the airplane on August 18, 2016, at an airframe total time of 5,262.0 hours. At the last annual inspection, airframe total time was 6,272 hours, and engine time since new was 1,010 hours. At the accident, engine time since new was 1,134 hours.
An oil analysis from the last oil change on August 16, 2021, showed increased levels of chromium, iron, and nickel. The nickel level at 51 parts per million was about 34% higher than the 38 ppm from a previous analysis. The material composition of the exhaust valve stem and valve guide included significant nickel. The oil analysis report noted increased metal wear but did not consider it an immediate concern if levels did not trend upward. The engine had accumulated 20 hours since the last oil change, and maintenance documentation showed no evidence of unresolved engine issues.
Wreckage and Impact Examination
Postaccident examination revealed substantial damage to the engine mount and lower fuselage structure. A partial engine teardown found that the No. 2 cylinder exhaust valve was fractured. The National Transportation Safety Board Materials Laboratory examined the cylinder assembly. The exhaust valve head was embedded in the cylinder head adjacent to the intake valve seat. The intake valve head was fractured in multiple locations and pushed through the seat. The exhaust valve seat was missing; the cylinder head material around the exhaust outlet showed erosion and impact damage.
The exhaust valve fractured near the stem-to-fillet transition. The fracture surface exhibited a flat morphology with ratchet marks, consistent with crack initiation at that location. The origin was obscured by damage. Away from the origin, curved crack arrest marks and features consistent with fatigue fracture were observed. The valve stem surface had no pitting or erosion.
Clearance from the exhaust valve stem to the valve guide in the upper and middle thirds was 0.0067 and 0.0111 inch, respectively. The manufacturer's service limit is 0.0085 inch. Clearance from the exhaust rocker arm shaft to the rocker arm bearing was 0.0032 and 0.0041 inch at the inboard and outboard ends; the service limit is 0.0040 inch.