What happened
On June 4, 2021, an Air Tractor AT301, registration HK-4953, was performing agricultural spraying operations near Ciénaga, Magdalena. After completing an initial flight, the aircraft took off for a second mission from the La Lucha airstrip. During the climb, at an altitude of approximately 656 feet, the engine experienced a significant loss of power accompanied by intense noise and vibration, shortly followed by a total engine shutdown.
The pilot immediately discharged the chemical payload to reduce weight and attempted to restart the engine using the manual fuel pump, but was unsuccessful. As the aircraft lost airspeed and altitude, the pilot identified a nearby banana plantation for an emergency landing. While maneuvering at a very low altitude, the aircraft struck a cable used for transporting banana bunches. This impact caused a loss of control, leading the aircraft to strike the ground and impact several banana plants.
The pilot sustained one minor injury to the knee and was able to exit the aircraft independently. The aircraft sustained substantial damage, including the engine detaching from its mounts and the left wing separating from its primary support.
The investigation
The GRIAA investigation focused on the mechanical failure of the powerplant. Metallurgical analysis, including scanning electron microscopy (SEM) and hardness testing, was conducted on the engine components. The investigation examined the maintenance records of the operator, the flight history of the day, and the structural integrity of the engine cylinders.
Investigators analyzed the fracture patterns on the engine's cylinder No. 7. The study also reviewed the operator's maintenance manuals, specifically looking for procedures regarding component life limits, inspection intervals, and engine stabilization protocols during agricultural operations.
Findings
- The primary cause of the accident was an engine failure resulting from the fracture of cylinder No. 7.
- The fracture was likely caused by material aging, fatigue, or stress concentration within the cylinder.
- The pilot had reduced engine power to minimum operational levels to mitigate high vibrations, which inadvertently led to a loss of compression and the eventual engine shutdown.
- The operator's maintenance program lacked specific procedures to limit the service life of engine cylinders or to track the real-time operational life of these components.
- There were deficiencies in the maintenance manual regarding written inspection procedures for critical engine components.
- There was evidence suggesting that crews may not have consistently adhered to manufacturer-recommended engine stabilization and cooling times during operations.