Incident Overview
An aircraft experienced a sudden loss of engine power during cruise flight. The pilot first noted a rapid decrease in oil pressure, followed shortly by engine roughness. A loud knock was heard, after which the engine lost power and oil began to spray onto the windshield. The pilot attempted a forced landing on a road, but the aircraft collided with ground obstructions during the landing.
Post-Accident Examination
Disassembly of the engine revealed only trace amounts of oil remaining in the case. The number 3 and 4 connecting rods exhibited heat distress consistent with oil starvation. During inspection of the propeller governor mounting area, investigators found an MS9144-01 screen gasket installed between the governor and its mounting pad. An oil path was observed running between the gasket and the pad, from the high-pressure oil port to the outside edge of the pad.
Maintenance History
Maintenance records indicated that 1.4 flight hours prior to the accident, the propeller governor had been removed for repair and then reinstalled on the engine. The mechanic who performed the work and the inspector who reviewed the installation both stated that they used the current Cessna 177 maintenance and parts manuals for procedural guidance. Both individuals said they were unaware of any special gasket stack requirement for this particular engine model and noted that they would not routinely refer to engine-specific manuals for a governor installation, as the governor is considered an airframe component.
Manual Discrepancies
Review of Lycoming publications from 1987 revealed that this specific engine requires a unique combination of a gasket and a plate to prevent oil leakage between the governor and its mounting pad. However, the Cessna service manual only addresses the installation of the MS screen gasket, referring to it in the singular as 'gasket'. The special Lycoming gasket and plate are not mentioned in either the Cessna service or parts manuals. Cessna Aircraft later confirmed that they were aware of the Lycoming requirement for a special gasket stack in the Cessna 177RG application and stated that they were in the process of revising the relevant service and parts manuals accordingly.