What happened
On December 8, 2019, an Ayres S2R-G10, registration LV-BFT, was conducting agricultural spraying operations near Los Frentones, Chaco. After approximately 30 minutes of flight, while performing the third pass over a crop, the aircraft's engine suffered a sudden loss of power followed by a complete shutdown.
At the time of the failure, the aircraft was flying at an altitude of approximately three meters. To avoid trees in the flight path, the pilot executed a right-hand turn and performed an emergency landing in the field. During the landing sequence, the aircraft traveled 89 meters before the left main landing gear collapsed. The pilot was able to exit the aircraft without injury.
The investigation
The investigation focused on the mechanical failure of the Honeywell TPE331-10-511M engine. While fuel and oil samples were found to be suitable, the engine's lubrication system's chip detector contained significant amounts of metallic debris. Spectrometric analysis of the main oil filter revealed traces of stainless steel, copper, silver, aluminum, and carbon, along with glass beads.
Physical inspections of the engine revealed several critical issues: the propeller shaft was off-center, the oil injectors were obstructed by metallic particles, and sealant was partially blocking the oil drain channel in the nose cone. Crucially, investigators found that a gear associated with the torque sensor within the reduction gearbox had detached. This gear showed abnormal wear patterns, and an adjacent gear exhibited irregular oscillations during rotation.
Findings
- The engine loss of power and subsequent shutdown were caused by the detachment of the torque sensor gear.
- This mechanical failure interrupted the kinematic chain, preventing the transmission of movement to the fuel and oil pumps or control unit.
- The aircraft had a history of a similar incident in 2013, which also involved the failure of the torque sensor gear; however, records regarding the previous repair could not be retrieved due to expired document retention periods.