What happened
On December 29, 2014, an AT-502B agricultural aircraft, registration PR-AEJ, was performing a local spraying mission near Fazenda Ubiratá in Primavera do Leste, Mato Grosso. While executing a repositioning turn to apply pesticides, the aircraft experienced a loss of control, striking trees before impacting the ground at a 30-degree nose-down angle. The aircraft sustained substantial damage to the engine, wings, hopper, stabilizers, landing gear, and fuselage. The pilot sustained minor injuries.
The investigation
CENIPA investigators analyzed data retrieved from a Differential Global Positioning System (DGPS) onboard the aircraft. The investigation established that the aircraft was within weight and balance limits, carrying 1,000kg of chemical product and 400 liters of fuel. However, the DGPS data revealed that the pilot was frequently operating outside the aircraft's safe aerodynamic envelope. Specifically, the aircraft reached speeds of up to 147kt, exceeding the maximum structural speed (VNE) of 135kt. Conversely, during the high points of repositioning turns, the aircraft's speed dropped near or below the stall speed.
Investigators also noted that while the pilot was experienced in agricultural spraying, this was his first season operating the AT-502B model. The investigation examined whether the loss of control was caused by a low-speed stall during a turn or a high-speed stall (accelerated stall) resulting from an aggressive pitch input to avoid terrain.
Findings
- Exceeding speed limits: The pilot intermittently operated the aircraft beyond its prescribed flight envelope, alternating between speeds exceeding VNE and speeds approaching the stall threshold.
- Pilot judgment: The pilot failed to observe the operational parameters required for safe flight, judging that the aircraft could handle speeds exceeding the manufacturer's limits.
- Loss of control: The loss of control was likely triggered by either a stall at the top of a turning maneuver or an accelerated stall caused by an abrupt pitch command intended to recover altitude.
- Operational attitude: The lack of adherence to the flight manual's speed and maneuver constraints compromised flight safety during low-altitude operations.