What happened
On November 19, 2012, an Air Tractor AT-301, registration HK-3289, was performing agricultural spraying operations over the Maria del Rosario farm in Turbo, Antioquia. The aircraft, operated by Servicios de Fumigacion Aerea Garay S.A.S, had been conducting flights since early morning from the Los Almendros aerodrome.
While executing a turn to begin a new spray pass, the pilot experienced a sudden and intense vibration in the engine that made the aircraft nearly impossible to control. The pilot immediately reduced power and attempted an emergency landing in an unprepared, cultivated field. During the descent, the aircraft struck a banana plantation and collided with a product transport line before impacting the ground. The impact caused significant structural damage to the airframe, including the separation of the engine and the horizontal stabilizers.
The pilot, the sole occupant, was found unconscious by farm workers. He sustained serious injuries, including polytrauma to the left foot and right hand, and a fracture to the right knee. No post-crash fire occurred.
The investigation
The GRIAA investigation focused on the mechanical integrity of the powerplant and propeller. The investigation examined the maintenance history of the Pratt & Whitney R1340 AN-1 engine and the Hamilton Standard 2/2 D 40 propeller. Records showed that the aircraft had been involved in previous incidents, and the propeller had undergone various services and replacements due to oil leaks.
Post-accident inspections of the engine revealed a loose carburetor, dented intake tubes, and a broken ignition ring. While the internal mechanical components of the engine were found to be operating normally until the impact, the investigation identified a critical failure in the propeller assembly.
Findings
- The primary cause of the engine vibration and subsequent loss of control was a fracture of a propeller blade.
- The failure was attributed to transgranular fatigue, which led to a crack propagation and the eventual sudden ductile fracture of a segment of the blade.
- The propeller failure was not caused by an external impact.
- The pilot's use of a flight helmet, chest harness, and abdominal belt was instrumental in the aircraft's high survivability and the mitigation of the pilot's injuries.
Safety action
- The investigation recommended that the operator implement stricter quality control procedures for propeller inspections and maintenance.
- It was suggested that the company establish a specialized monitoring program for this propeller model, utilizing non-destructive testing (NDT) to detect internal defects invisible to the naked eye.
- Recommendations were made for pilots to enhance pre-flight and post-flight inspections, specifically focusing on the operational condition of propeller blades.