What happened
On May 15, 2021, a Cessna 172 was conducting a dual-instruction flight from Guaymaral, Colombia, on a route toward Ibagué and Barrancabermeja. While flying over the town of Tenjo at approximately 10,000 feet, the aircraft experienced a sudden and substantial loss of power accompanied by intense noise and vibrations.
The instructor pilot attempted several engine restarts, but all attempts were unsuccessful. Realizing the aircraft could not return to Guaymaral, the instructor decided to perform an emergency landing in an unprepared field. The aircraft landed under control in a potato field; however, during the landing roll, the nose gear struck a furrow in the terrain. This impact caused the aircraft to pivot violently on its transverse axis, resulting in a 180-degree inversion (capsize). Both the instructor and the student pilot evacuated the aircraft on their own; they sustained no injuries.
The investigation
The GRIAA investigation focused on the mechanical failure of the engine and the maintenance oversight of the operator. Investigators examined the engine components, specifically the crankshaft and connecting rods, and performed metallographic and fractographic analyses. The investigation also reviewed the operator's maintenance manuals, inspection procedures, and the traceability of engine components.
Findings
- The primary cause of the engine failure was the fracture of connecting rod No. 3, which led to an immediate loss of power.
- The failure originated from a defect in the crankshaft journal surface, where a partial absence of the nitrided layer caused fissures and inadequate lubrication. This material loss likely occurred during a grinding process following nitriding, which reduced the component's fatigue resistance.
- The operator lacked adequate procedures for inspecting and documenting the technical history of engine components, making it impossible to determine the actual life cycles of internal parts.
- There was a lack of effective quality control regarding the traceability of the engine, particularly regarding its history under previous operators.
- The operator's maintenance manual provided insufficient guidance for quality control personnel regarding the inspection and receipt of critical components.