Accident Overview
On March 25, 2024, at approximately 1100 central daylight time, a Cessna T210M airplane, registration N498TB, was substantially damaged in an accident near San Saba, Texas. The pilot, the sole occupant, was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal cross-country flight.
Pilot's Account
According to the pilot, during the cross-country flight, the engine manifold pressure began to decrease slowly. He elected to divert and initiated a descent for a precautionary landing. During the descent, the oil pressure gauge dropped to zero, and the propeller began to overspeed. The pilot had the airport in sight when smoke started coming from the engine cowling as he aligned the airplane with the runway. He lowered the landing gear but kept the flaps retracted as the airplane approached aerodynamic stall speed. The airplane landed approximately 100 yards short of the runway in wet grass. The landing gear dug into the terrain, and the airplane came to rest inverted, resulting in substantial damage to the fuselage and wings.
After egressing, the pilot noticed a small fire near the engine compartment and used a handheld fire extinguisher to suppress it.
Engine Data Analysis
The airplane was equipped with a digital engine monitor. Review of the recovered data revealed that about 37 minutes into the flight, engine oil pressure began a steady decrease while the airplane remained at about 11,000 ft. Manifold pressure, fuel pressure, and fuel flow were unremarkable until about 1 hour 7 minutes into the flight, when oil pressure briefly dropped to 22 psi. The airplane stayed at 11,000 ft until about 1 hour 16 minutes, when oil pressure fell to as low as 3 psi. As altitude rapidly decreased, engine rpm briefly increased from 2,500 to about 4,100 rpm. For the remainder of the flight, oil pressure fluctuated between 4 and 18 psi, manifold pressure between 10 and 18 inHg, and engine rpm steadily decreased. The final recorded data, at about 1 hour 19 minutes, showed 8 psi oil pressure, 28.6 inHg manifold pressure, 386 rpm, 4.9 gallons per hour fuel flow, 1.4 psi fuel pressure, and altitude 1,254 ft msl (about 20 ft agl).
Postaccident Examination
The airplane had been modified by a supplemental type certificate for a turbo-normalized Continental IO-550-P engine. Examination of the engine revealed several holes on the top of the crankcase, and the engine was seized and could not be rotated. During disassembly, metal pieces of various sizes were found throughout the oil system. The oil pump showed no blockages but had rotational scoring. Multiple connecting rods were damaged and separated, and their bearings were not identifiable. The disassembly showed several areas of thermal distress consistent with lack of oil lubrication. The turbocharger had no anomalies.
Only a small amount of oil was observed within the engine during disassembly, with no substantial oil found on the engine, firewall, cowling, or fuselage. No other oil leak source was identified besides the holes in the upper crankcase.
The pilot reported that the day before the accident, he changed the engine oil and added 9 quarts of oil.