What happened
On December 21, 1999, a PA-25-235 operated by Aeroagrícola Chapadão was performing low-altitude crop spraying over a sugarcane plantation at Sítio Santa Adélia, in São Carlos, São Paulo. The aircraft was on its ninth flight of the afternoon, carrying 400 liters of herbicide in its hopper.
After completing the first spray pass, which consumed 100 liters of the product, the pilot attempted to accelerate for a return maneuver. During this phase, the engine experienced a significant power loss, dropping to approximately 30% of its rated output. In an attempt to maintain flight, the pilot jettisoned the remaining 300 liters of herbicide. However, the sudden shift in the center of gravity, combined with the pilot's failure to apply immediate nose-down pitch compensation, caused the aircraft to pitch up sharply. This maneuver led to an aerodynamic stall, resulting in a nose-down impact with the ground. The aircraft sustained severe damage, and the pilot sustained serious injuries.
The investigation
CENIPA investigators examined the aircraft's maintenance history and the operational environment. The investigation noted that the engine had been exhibiting excessive oil consumption during the eight previous flights that afternoon, a condition the pilot had reported to the operator. The investigation also analyzed the aircraft's trim settings, finding the elevator compensator deflected in a nose-up position at the time of impact.
While the exact cause of the engine power loss remained a subject of hypothesis—with investigators considering both a potential fuel exhaustion due to improper planning and the effects of excessive oil consumption—the physical evidence pointed toward a loss of control following the load jettison. The investigation also highlighted a lack of corrective action by the company regarding the reported engine issues.
Findings
- Inadequate Pilot Compensation: The pilot failed to apply the necessary nose-down elevator input to counteract the pitch-up tendency caused by the rapid shift in the center of gravity following the herbicide jettison.
- Operational Pressure: The pilot continued to fly the aircraft despite known engine irregularities due to perceived professional pressure and the risk of financial penalties or job loss.
- Deficient Supervision: The operator failed to adequately supervise flight operations and did not implement corrective maintenance for the engine's excessive oil consumption.
- Maintenance and Planning: The investigation identified potential deficiencies in maintenance oversight and the possibility of inadequate fuel planning for the mission.