What happened
On October 19, 2022, a Thrush S2R-H80, registration PP-PRD, was performing an agricultural spraying mission near Ipuã, São Paulo. Shortly after departing from a landing strip at Fazenda Valinhos, the aircraft began a right-hand turn toward the application area when the pilot noticed a significant reduction in available engine performance.
In response to the power loss, the pilot executed an emergency landing in a nearby crop field. Before impacting the ground, the pilot successfully jettisoned the agricultural payload. During the landing impact, the landing gear assembly broke, and the propeller group struck the ground. The pilot survived the accident without injury, though the aircraft sustained substantial damage.
The investigation
CENIPA investigators analyzed the engine monitoring data from the aircraft's MVP-50T glass panel system, covering the 50 flights preceding the accident. The investigation focused on the behavior of the engine's Starting and Limiting Unit (SALM) and the BETA valve.
Physical examination of the wreckage revealed that the propeller governor had been torn from its housing. The engine was found to be seized due to internal deformations caused by the impact. Analysis of the propeller blades showed that some were in a feathered position, while others showed signs of high rotation at the moment of impact. The investigation also noted abnormal fluctuations in the BETA valve parameters during both the accident flight and the flight immediately preceding it.
Findings
- The investigation identified an unexpected activation of the SALM system, which reduced the fuel flow to the engine. While the gas generator speed (NG) remained within normal parameters, the propeller speed (NP) was restricted to a maximum of 1,900 RPM.
- The propeller blades moved into a feathered position, which caused the loss of power despite the engine maintaining adequate rotation.
- There was evidence of an electrical malfunction that likely triggered the SALM system erroneously. This same electrical issue may have compromised the BETA switch indicator lights, preventing the pilot from receiving a visual warning of the propeller's abnormal state.
- The pilot was fully qualified, with valid medical certification and extensive experience in the aircraft type.
- The aircraft was within weight and balance limits, and all maintenance records and airworthiness certificates were up to date.