What happened
On June 23, 2008, a CESSNA 177 RG “Cardinal”, registration EC-GCX, was performing a scheduled check flight following an annual inspection at Madrid-Cuatro Vientos Airport. The flight was intended to verify the aircraft's airworthiness for certificate renewal.
While flying at 4,000 feet near Villaviciosa de Odon, the pilot detected a loss of thrust and a sudden increase in engine RPM, which exceeded the maximum allowable limit of 2,700 RPM. The pilot attempted to adjust the propeller pitch, but the control was unresponsive. As the pilot attempted to maintain power to glide back to the airport, the engine experienced severe vibrations and oil smoke entered the cockpit.
Unable to reach the runway, the pilot executed an emergency landing in a wheat field approximately 4.5 km west of the airport. The pilot was uninjured, though the aircraft sustained significant damage to the engine and propeller.
The investigation
The CIAIAC investigation focused on the mechanical failure of the Lycoming IO-360 engine and the propeller governor installation. Post-incident inspections of the engine revealed a large amount of metallic shavings in the crankcase and significant damage to the connecting rods of the No. 2, 3, and 4 cylinders, which showed signs of severe overheating. A hole was also discovered in the engine crankcase.
Investigators examined the propeller governor installation and found an oil leak at the coupling between the governor and the engine. The inspection revealed that only a single gasket had been used during the recent overhaul, rather than the two gaskets and a specialized plate required by Lycoming Service Instruction 1438A to prevent such leaks.
Findings
- The primary cause of the engine damage was an oil leak at the propeller governor-engine coupling, which led to a gradual reduction in engine oil levels and insufficient lubrication.
- The loss of lubrication caused the engine's moving parts to overheat, increasing torque and causing the governor to reduce the propeller blade pitch to its minimum setting.
- This sudden change in pitch resulted in an engine overspeed condition, which further aggravated the mechanical damage to the connecting rods and crankshaft.
- A contributing factor was that the maintenance center's electronic manual did not include the necessary Temporary Revision 5, which detailed the correct, multi-gasket installation procedure for the governor.