What happened
On November 6, 2013, an AT-402A aircraft, registration PR-BMS, was performing an agricultural spraying operation over a cotton plantation at Fazenda Santa Luzia in Sapezal, Mato Grosso. During the takeoff roll on a compacted dirt runway, a warning light for the fuel filter illuminated on the instrument panel.
In response to the alarm, the pilot initiated an aborted takeoff procedure. During the deceleration, the aircraft drifted toward the left edge of the runway. As the pilot attempted to correct the deviation, the aircraft's landing gear encountered a significant slope at the edge of the runway, leading to a loss of control. The aircraft exited the left side of the runway, resulting in the propeller blades striking the ground and the failure of the right main landing gear strut. The aircraft sustained substantial damage to the engine, propeller, right wing, and landing gear, but the pilot escaped without injury.
The investigation
CENIPA investigators examined the aircraft's systems and the operational conditions at the time of the accident. The investigation focused on the cause of the fuel filter warning and the pilot's decision-making process. Technical analysis revealed that the fuel filter itself was not clogged; instead, a pressure switch (PN E1S-R-VAC) was malfunctioning, sending a continuous false signal to the cockpit.
Investigators also reviewed the aircraft's weight and balance, finding that the aircraft was operating 780kg above its maximum takeoff weight. The investigation further analyzed the runway geometry, noting a significant downward slope from the center to the left side of the runway, which exacerbated the excursion.
Findings
- The pilot's attention was fixated on the warning light, causing a loss of external visual references.
- The decision to not jettison the hopper load (1,500kgf) to reduce weight during the emergency made the aircraft more difficult to control.
- The aircraft was operating significantly above its maximum allowable takeoff weight.
- The pilot applied excessive rudder input to correct the deviation, which induced a significant yaw to the left.
- The runway surface had a significant lateral slope toward the left, contributing to the excursion.
- The pilot lacked specific training or simulator experience for handling unexpected cockpit warnings in agricultural operations.