What happened
On August 8, 2014, a Piper PA-25-260, registration HK-1680, was performing agricultural spraying operations over rice crops at Finca Boluga in Venadillo, Tolima. The aircraft, operated by Sanidad Vegetal Cruz Verde S.A.S., had successfully completed three flight segments of its scheduled eight-flight mission under favorable weather conditions.
During the fourth flight, while the pilot was compensating for a turn during the application of fertilizer, the control stick detached from its structural anchor. This sudden failure left the pilot without the ability to control the aircraft'-s ailerons or elevators. The aircraft entered a sharp left turn and continued to roll along its longitudinal axis until it inverted. The aircraft subsequently impacted the ground, causing the right wing to fracture and fold under the fuselage. The landing gear detached upon impact, and the aircraft slid through the field before coming to a halt. The pilot sustained severe injuries but survived the impact.
The investigation
The GRIAA investigation focused on the structural integrity of the flight control system. Components including the control stick assembly and the torque tube assembly were analyzed using metallographic examinations at the NTSB laboratories in the United States. Investigators examined the maintenance logs, which showed that the aircraft had been undergoing regular 50, 100, 500, and 1000-hour inspections, and that the most recent service had been completed in July 2014.
Findings
- The investigation established that the primary cause of the accident was a brittle fracture in the sheet metal connecting the control stick to the torque tube, resulting from material fatigue.
- A contributing factor was the high number of bending load cycles applied to the torque tube sheet due to lateral movements of the control stick.
- Evidence suggested that the pilot's highly efficient operational style, characterized by rapid flight segments, may have involved aggressive control inputs that accelerated the fatigue process.
- Metallographic analysis also revealed manufacturing deficiencies, including assembly errors and material imperfections within the component structure.