What happened
On November 13, 2009, an AT-401B agricultural aircraft, registration PT-WFG, was performing a fertilizer spraying mission at Fazenda Vista Alegre in Três Lagoas, Mato Grosso do Sul. During the third takeoff attempt of the day, the aircraft failed to reach its required rotation speed of 70 knots.
Recognizing the loss of performance, the pilot attempted to abort the takeoff by applying the brakes. However, the aircraft could not be stopped within the remaining runway limits. The aircraft overran the end of the grass runway, collided with a wooden fence, and ended up in an inverted position. The pilot was uninjured, but the aircraft sustained severe damage to the engine, propeller, vertical stabilizer, and cockpit.
The investigation
CENIPA investigators determined that the primary cause of the accident was an extreme weight imbalance. While the aircraft's maximum takeoff weight (MTOW) is 3,565 kg, the investigation revealed that the aircraft was operating at approximately 4,158 kg—roughly 593 kg over the manufacturer's limit.
This excess weight was due to the hopper being completely filled with urea fertilizer, which has a high density. The investigation found that the ground crew and the pilot failed to accurately calculate or communicate the weight of the cargo being loaded. The investigation also noted that the pilot's decision to abort the takeoff was likely delayed, which, combined with the reduced braking and acceleration performance caused by the overload, made the runway excursion unavoidable.
Findings
- Inadequate flight planning: The pilot and ground personnel failed to verify the total weight of the aircraft before takeoff.
- Operational error: The aircraft was loaded with a cargo weight that exceeded the manufacturer's maximum takeoff weight by nearly 600 kg.
- Pilot judgment: The pilot's decision to continue the takeoff roll until a late stage contributed to the inability to stop before the runway end.
- Support personnel error: The ground crew was unable to provide accurate information regarding the weight of the fertilizer being loaded into the hopper.