What happened
On May 19, 2022, at approximately 20:58 local time, a Piper PA-28-180 Cherokee, registration OB-1795, was conducting a night flight training mission under IFR conditions near Pisco International Airport (SPSO). The flight, operated by a flight school, involved an instructor and a student pilot performing instrument approach procedures.
During a climb following a touch-and-go maneuver at approximately 2,500 feet, the engine began to lose power progressively. The instructor took control of the aircraft and attempted several emergency procedures, including activating carburetor heat and switching fuel tanks, but the power loss continued. After declaring a 'Mayday' to the Pisco Tower, the instructor determined that the aircraft could not return to the runway due to insufficient altitude and airspeed.
The instructor opted for an emergency landing in an open area near a gas plant, avoiding power lines and obstacles. During the final approach, the crew prepared for an impact by shutting down systems and opening the cabin door. The aircraft struck a sand dune, which caused the landing gear to collapse and resulted in significant structural damage to the fuselage and propeller. The crew evacuated the aircraft without serious injuries.
The investigation
The CIAA investigation focused on the mechanical failure of the engine. Investigators examined the internal components of the engine and found a complete helical fracture of the crankshaft. The inspection revealed that the crankshaft featured surface and microstructural defects consistent with low-cycle fatigue.
Furthermore, the investigation identified the absence of the connecting rod bearing for cylinder #4, which had caused direct friction against the crankshaft. Evidence of severe thermal wear was also found on the main bearing, indicating operation under extreme lubrication limits. Additionally, investigators discovered that the installed crankshaft (P/N 94970) was not approved for the Lycoming O360-A3A engine model and lacked a visible serial number, presenting a failure in component traceability.
Findings
- The primary cause of the accident was a fatigue fracture of the crankshaft rod journal, resulting from surface and microstructural defects combined with a progressive loss of lubrication in the bearings, leading to catastrophic engine failure.
- The destruction of the connecting rod bearing for cylinder #4 caused direct friction and the generation of metallic debris within the engine.
- The installation of an unapproved crankshaft lacking proper identification and traceability contributed to the difficulty in monitoring the component's integrity.
- Thermal damage in cylinders #3 and #4 suggested anomalous combustion or lean mixture conditions, increasing mechanical stress on the crankshaft.
- The aircraft was operating within weight and center of gravity limits, and the crew managed the emergency procedures effectively.