What happened
On September 9, 2011, a Piper PA-25-260 performing agricultural spraying operations departed from Casa Branca, SP, to apply herbicide at Fazenda Barra Bonita in Itobi, SP. The pilot was executing the first pass of the day, replacing another pilot who was originally scheduled for the mission.
While performing a repositioning turn, known as a "balloon" maneuver, the aircraft encountered a sudden and significant tailwind. The pilot struggled to maintain control of the aircraft and experienced a rapid loss of altitude. In an attempt to reduce the rate of descent, the pilot jettisoned the entire herbicide payload approximately 70 meters from the impact site. Due to the aircraft's low altitude and the rising terrain ahead, the plane struck the ground in a pasture area, resulting in a post-crash fire that completely destroyed the aircraft. The pilot survived the accident without injuries.
The investigation
CENIPA investigators established that while the pilot was experienced in this type of flight and the aircraft was airworthy and within weight and balance limits, there were significant atmospheric changes occurring. During the initial marking pass, the pilot received radio information that surface winds at the departure airfield, located 7 nautical miles away, had increased significantly to approximately 30 knots. The investigation focused on the interaction between the sudden tailwind, the aircraft's descent rate, and the terrain gradient.
Findings
- Inadequate flight planning, as changes in atmospheric conditions, specifically regarding wind intensity, were not properly verified.
- Encounter with adverse meteorological conditions, specifically significant tailwind gusts.
- The combination of the terrain slope and the high rate of descent caused by the wind made the aircraft difficult to control at low altitude.
- The pilot's medical certificate (CCF) was expired at the time of the occurrence.