What happened
On May 25, 2022, a student pilot was conducting a solo navigation training flight in a Cessna 152 departing from Melipilla Aerodrome (SCMP). While cruising at 3,500 feet near the "Las Arañas" crossing, the pilot noticed smoke entering the cockpit. Upon maneuvering toward the "El Alba" sector, the engine began to vibrate violently, followed by a perceived explosion and a total loss of engine power.
In response to the engine failure, the pilot executed an emergency landing on a field in the Fundo las Tinajas area. During the landing sequence, the aircraft slid across the terrain and struck a group of trees. The impact and subsequent movement caused the aircraft to catch fire, resulting in the total destruction of the Cessna 152. The pilot sustained minor injuries.
The investigation
DGAC Chile investigators examined the wreckage and the Lycoming O-235-L2C engine. The inspection of the engine revealed that cylinder number two had become detached from the engine block. This failure was accompanied by the shearing of two cylinder studs and a fracture in the crankcase. The investigation also identified oily residue on the fuselage, indicating a significant loss of lubrication during the flight.
Technical analysis of the engine block showed evidence of pre-existing fatigue cracks. These cracks had propagated into a brittle fracture that circled the base of the cylinder support, leading to the structural failure. While the engine had recently undergone an overhaul and was operating with relatively low hours since its installation, the exact timing of the formation of these fatigue cracks could not be determined.
Findings
- The primary cause of the engine shutdown was the fracture of the engine crankcase at the base of the cylinder number two support.
- Pre-existing fatigue cracks in the cylinder mounting area acted as a contributing factor to the structural failure.
- The loss of cylinder support and the resulting crankcase fracture led to the vibrations and power loss reported by the pilot.
- The engine experienced a loss of lubrication due to the fracture, evidenced by overheating in the crankshaft components.
- Maintenance records showed the aircraft and engine were compliant with approved maintenance programs and were within their inspection intervals.