What happened
On January 13, 2018, a Thrush S2R-T34 aircraft, registration PR-GAT, was performing an agricultural spraying mission near Formosa do Rio Preto, Bahia. After completing the application of pesticides approximately 25km from the airfield, the pilot returned to the Fazenda Barcelona V Aerodrome for landing.
Although weather conditions were initially favorable, recent rainfall had left the unpaved, dirt runway wet. During the landing approach, the pilot maintained a speed of 95 mph, which exceeded the maximum recommended speed of 92 mph specified in the aircraft's flight manual. Upon touchdown, the aircraft experienced a loss of directional control, initially drifting to the right before veering sharply to the left. The aircraft struck a small elevation on the left side of the runway, which caused the main landing gear to separate, before finally coming to a stop in a nearby cornfield. The pilot was uninjured, but the aircraft sustained substantial damage.
The investigation
CENIPA investigators examined the runway conditions and the aircraft's flight parameters. Satellite imagery confirmed the presence of cumulonimbus clouds and moisture in the area, consistent with the pilot's report of recent rain. The investigation focused on the phenomenon of viscous hydroplaning, which can occur on unpaved surfaces when uncompacted earth and water create a slippery layer that prevents tires from maintaining contact with the ground.
Investigators also analyzed the pilot's use of aircraft controls. It was noted that the pilot prioritized the use of brakes immediately after touchdown rather than utilizing aerodynamic braking methods like reverse thrust. Additionally, the investigation looked into whether the nosewheel had unlocked prematurely, a condition noted in the manual as a potential cause for loss of control during turns.
Findings
- The aircraft approached the runway at a speed exceeding the manufacturer's maximum limit.
- The runway surface was wet and composed of dirt, creating conditions highly susceptible to viscous hydroplaning.
- The pilot's application of controls contributed to the incident, specifically the prioritization of braking over reverse thrust and the failure to properly assess the hydroplaning risk.
- The pilot's judgment regarding the landing technique under slippery conditions was noted as an indeterminate contributing factor.