What happened
On July 19, 2012, an Air Tractor 802A, registration EC-JLB, was participating in a coordinated aerial firefighting mission near the Caldeirão mountains in the Algarve region of Portugal. The aircraft was part of a four-plane formation tasked with suppressing a forest fire. After refueling with fuel at Beja Air Base, the group proceeded to the Roxo Dam to perform "scooping" operations—a technique where amphibious aircraft skim the water surface to rapidly intake water into their tanks.
As the fourth and final aircraft in the formation, EC-able positioned itself to the far left of the group's flight path to avoid the waves generated by the preceding aircraft. During the takeoff run from the reservoir, the aircraft encountered significant wake turbulence created by the three preceding planes. The wind, blowing from the northwest at approximately 20 km/h, pushed the wake from the earlier aircraft directly into the path of the trailing plane.
The pilot experienced a temporary loss of control, and the aircraft drifted significantly to the left. Before the aircraft could achieve lift-off, the floats struck the shoreline. The impact tore away the left float, and the aircraft skipped over a small strip of land before nose-diving into another arm of the reservoir. The aircraft subsequently sank.
The investigation
The GPIAAF investigation focused on the flight dynamics during the group scooping maneuver and the impact of environmental factors. Investigators examined the aircraft's maintenance records, which showed the plane was airworthy and had undergone recent inspections. The investigation also reviewed the operator's flight manual and the specific formation used during the mission.
Findings
- The primary cause of the accident was the pilot's temporary loss of control of the aircraft, which caused a lateral deviation toward the shoreline.
- The use of a left-side line formation while facing a crosswind from the right caused the wake turbulence from preceding aircraft to be deflected directly onto the trailing aircraft.
- There was inadequate planning for the group refueling maneuver, specifically failing to account for how crosswinds would affect the propagation of wake turbulence.
- The pilot was unable to maintain the necessary distance from the shore due to the turbulence-induced difficulty in controlling the aircraft's flight path.
Safety action
- The GPIAAF issued a safety recommendation to the operator, AVIALSA T-35, to update its Operations Manual with more detailed procedures regarding the effects of crosswinds during group scooping operations. The recommendation emphasizes the need to consider different formation types to minimize or avoid the negative effects of wake turbulence deflection.