What happened
On April 13, 2024, at approximately 14:30 local time, a private pilot departed from Viña del Mar Aerodrome (SCVM) for a recreational flight. While en route, the pilot of the Cessna 172N experienced significant engine vibrations accompanied by a loss of engine power. In response to the developing mechanical issue, the pilot declared an emergency and diverted to Rodelillo Aerodrome (SCRD) to perform an emergency landing. Both the pilot and the passenger exited the aircraft uninjured, though the aircraft sustained damage.
The investigation
DGAC Chile investigators examined the aircraft's engine following its transport to Viña del Mar. The inspection revealed that the engine was missing its propeller and showed traces of oil on various components. A detailed examination of the engine assembly identified that cylinder number 4 had become separated from the crankcase assembly at the top. The investigation noted that three studs were broken and one stud was missing its corresponding nut. Additionally, the rocker arm guide covers on the engine block were found to be misaligned.
Further analysis of the spark plugs showed that while the plugs for cylinders 1, 2, and 3 appeared normal, the plugs for cylinder 4 contained accumulations of incomplete combustion residue, indicating a malfunction within that specific cylinder. Specialized laboratory testing was conducted on the fractured studs from cylinder 4 to determine the nature of the failure.
Findings
- The engine suffered a mechanical failure characterized by the separation of cylinder number 4 from the crankcase assembly.
- The failure involved broken and missing cylinder studs and misaligned rocker arm guide covers.
- Evidence of incomplete combustion was present in the spark plugs of the affected cylinder.
- There was no evidence of fire or external impact during the landing sequence.