What happened
On March 21, 2019, an Air Tractor AT-802A, registration PR-MMF, was performing a takeoff roll at the Fazenda Nova Floresta Aerodrome in Caiabu, São Paulo, for an agricultural spraying mission. During the acceleration phase, the left main landing gear leg fractured. This structural failure caused the aircraft to veer to the left, eventually coming to a stop approximately 15 meters off the runway. The pilot was uninjured, but the aircraft sustained substantial damage to the left main gear, the spraying equipment, the left wing tip, and the propeller blade tips.
The investigation
CENIPA investigators examined the fractured component and identified a 24 mm deep and 9/5 mm wide pre-crack characterized by "beach marks," which are definitive indicators of fatigue failure. The investigation also revealed several corrosion pits located on a portion of the gear leg that lacked paint protection.
Further scrutiny of the aircraft's maintenance records revealed significant discrepancies. The annual inspection for the landing gear had been overdue since October 2012, and several 100-hour inspections had not been properly completed. Additionally, the maintenance logs for the airframe, engine, and propeller were not up to date. Investigators also noted that the aircraft was operating at a weight of approximately 6,322 kg, which exceeded the 5,700 kg load-bearing capacity of the grass runway surface.
Findings
- Fatigue failure of the left main landing gear leg, facilitated by corrosion pits in an unprotected area of the component.
- Inadequate maintenance oversight by both the maintenance organization and the aircraft operator, which failed to identify the developing corrosion and fatigue during required inspections.
- Incomplete maintenance records, including overdue annual inspections and improperly documented 100-hour inspections.
- Operational stress caused by operating the aircraft at a weight exceeding the structural resistance of the soft grass runway.
- Lack of detailed procedures in the aircraft's Owner's Manual regarding specific inspection tasks, which may have hindered the effective identification of the defect.