CEN22LA140

The pilot reported that he noticed the engine oil pressure dropped to 14 psi after he began the descent to his destination airport. He turned toward a nearby airport, but shortly thereafter the oil pressure dropped to 0 psi and the engine seized. The pilot executed a forced landing to a field and the airplane sustained substantial damage to its wings when it struck fences and livestock feeding troughs during the landing. Postaccident examination of the airplane revealed several missing and loose bolts securing the engine valve covers. The No. 4 cylinder valve cover was completely off and its gasket was not located after the accident. The No. 6 cylinder valve cover was very loose and was only held on by 4 of the 8 bolts normally used to secure the cover. The No. 4 cylinder valve arm shaft bolt was missing. Metal shavings were observed throughout the valve assembly area as well as deposited on the cowling and airplane along with the lost engine oil. Review of maintenance records did not reveal any recorded maintenance to the rocker covers since the most recent engine overhaul 6 years before the accident. Maintenance entries since the overhaul indicated routine maintenance, including annual/100-hour inspections and oil changes, with no leaks detected during post-maintenance engine runs. Attempts to discover when the rocker covers were last accessed for maintenance were unsuccessful. Based on the available evidence the loss of engine power was due to oil exhaustion that resulted from improper installation of the engine valve covers. Determination of when the improper maintenance was performed could not be determined based on the maintenance entries that were available.

On March 12, 2022, about 1245 central standard time, a Beech A36, N9410Q, was substantially damaged when it was involved in an accident near Heavener, Oklahoma. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the flight was from the Bentonville Municipal Airport/Louise M Thaden Field (VBT), Bentonville, Arkansas, to the Mena Intermountain Municipal Airport (MEZ), Mena, Arkansas. After beginning his descent into to the destination airport, he noticed a dramatic drop in oil pressure to 14 psi. He began to search for alternate airports since his destination was not reachable and the terrain was mountainous. He turned the airplane toward the west to attempt to reach the Robert S. Kerr Airport (KRKR), Poteau, Oklahoma, but within 1-2 minutes the oil pressure dropped to zero and the engine seized. The pilot executed a forced landing to a field. During the landing, the airplane struck fences and livestock feeding troughs, which resulted in substantial damage to the wings. Postaccident examination revealed that the engine No. 4 cylinder rocker cover was completely off, and the No. 6 cylinder rocker cover was only being held on by 4 bolts, all of which were very loose. The No. 4 cylinder rocker cover gasket was not located after the accident. The No. 4 cylinder rocker arm shaft bolt was missing. Multiple rocker cover bolt holes were elongated and embossed with the bolt thread pattern. Metal shavings were observed throughout the valve assembly area as well as deposited on the cowling and airplane along with the lost engine oil. Review of maintenance records revealed that the most recent maintenance on the engine was an oil change performed on December 22, 2021. The entry for the oil change noted that a post-maintenance engine run did not reveal any leaks and included no mention of work performed on the rocker covers. On November 17, 2021, an annual/100-hour inspection was performed on the engine. The entry for the inspection noted that a post-maintenance engine run was normal. A specific notation regarding leaks was not included in the endorsement. No mention of work performed on the rocker covers was noted. Further examination of the engine maintenance records showed that the engine had undergone an overhaul and was reinstalled on the airplane on November 2, 2016. Subsequent to the overhaul, several maintenance entries were made; however, none of the entries since the overhaul noted any work performed on the rocker covers of the engine. Interviews of personnel at the maintenance facility that performed the most recent overhaul revealed that approved hardware and gaskets were used to secure the rocker covers at the time of the overhaul. An interview of the mechanic that performed the most recent oil change revealed that he had not accessed the rocker covers and had no reason to while performing the oil change. Further attempts to discoverwhen the rocker covers were last removed were unsuccessful.