Accident Details
On June 4, 2020, at about 0955 central daylight time, a Beech A23A airplane, registration N7941L, sustained substantial damage when it impacted bushes and a tree during a forced landing near Cleburne, Texas. The private pilot, who was the sole occupant, was uninjured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Flight and Engine Malfunction
The pilot reported departing on a local flight at approximately 0925. He flew southwest along a local highway for several minutes before noticing that the oil pressure was trending toward the bottom of the green arc, although oil temperature remained normal. The pilot decided to return to the departure airport. During the turn, the engine began shaking. He reduced engine power to prevent severe shaking and then reapplied power to maintain altitude, at which point the engine stopped. The pilot did not recall if the propeller was windmilling but described the engine as silent. He executed a forced landing on a curving gravel road. As the road curved, the airplane departed the roadway, striking bushes and a tree, resulting in substantial damage to the right wing.
Postaccident Examination
Examination of the engine revealed that the No. 1 cylinder’s cylinder head had separated, exposing the piston. Further inspection showed wear on the tappets and camshaft. Small flakes of aluminum were present in the piston rod bearing, which exhibited scoring consistent with the passage of hard particles. The oil pump also showed heavy scoring witness marks indicative of hard particle passage. No other issues that would have precluded engine operation were found aside from the separated cylinder.
The No. 1 cylinder exhibited fatigue cracking through the cylinder wall over approximately 60° on the exhaust side, with secondary fatigue cracking on the intake side. The failure initiated from a through-wall crack on the exhaust side.
Maintenance History
A review of the airplane logbook revealed that on September 22, 2016, the total time since major engine overhaul was recalculated from 2,594.0 hours to 190.3 hours; however, no record of a major overhaul was found.
An entry dated August 15, 2016, indicated that debris was found under the oil pressure relief valve seat, which had caused the oil pressure gauge to read zero. Analysis of the oil found metal. According to the logbook, Continental Motors technical personnel recommended removing the pressure relief valve and checking for debris. The debris was cleared, and the valve was reinstalled with new washers. A subsequent test run showed normal oil pressure. Oil analysis revealed higher-than-normal wear particles. The logbook noted this was not a concern because two new cylinders had been installed within the previous 50 hours (which cylinders were replaced was not specified), and the engine had not been operated consistently. Spectro Oil Lab recommended operating the airplane for another 10 hours and then resubmitting a clean oil sample. No logbook entry confirmed that this was done. An oil and filter change and inspection were completed at the next annual inspection on February 7, 2017, with no mention of debris found.
On November 1, 2019, the oil pressure relief valve was removed, cleaned, and reinstalled, along with the oil temperature sensor. On June 2, 2020, the oil pressure relief valve seat was honed, and a new plunger was installed.