What happened
On May 5, 2010, an Embraer EMB-711ST, registration PT-NZO, departed from Morada Nova de Minas, MG, bound for Poços de Caldas, MG. During the takeoff roll, the pilot experienced heavy vibrations and an uncommanded braking sensation on the right side of the aircraft. Due to being near rotation speed, the pilot elected to continue the takeoff rather than abort.
Following takeoff, the pilot discovered that the right main landing gear would not lock in either the up or down position. After several unsuccessful attempts to secure the gear through various maneuvers, the pilot diverted to Poços de Caldas, which offered better emergency support. Upon arrival, the tower confirmed visually that the right gear was misaligned and protruding from the nacelle. The runway was prepared with foam, and the pilot executed a gear-up landing. The aircraft sustained light damage to the fuselage, landing gear, and flaps, along with severe damage to the propeller blades. Both occupants were unharmed.
The investigation
CENIPA investigators identified a broken pivot bolt in the right main landing gear torque link. Laboratory analysis by the Institute of Aeronautics and Space (IAE) revealed the presence of cracks and pitting corrosion near the fracture surface, along with a discontinuity in the cadmium plating. While the exact fracture mechanism could not be definitively determined because the fracture surface was deformed, the findings pointed toward corrosion-related fatigue.
The investigation also examined the aircraft's maintenance history and operational environment. The pivot bolt was an "on-condition" item requiring periodic visual inspections every 100 hours. Although maintenance logs were up to date, the corrosion and cracks were not detected during previous inspections. Furthermore, the aircraft frequently operated from unpaved airfields, such as Morada Nova de Minas, which featured uneven surfaces and potholes.
Findings
- The failure of the torque link pivot bolt prevented the right main gear from properly seating in the nacelle, making it impossible to lock the gear.
- Corrosion-induced fatigue or a momentary overload from operating on bumpy, unpaved runways likely contributed to the bolt failure.
- The degradation of the cadmium plating facilitated pitting corrosion, which led to the development of micro-cracks.
- Maintenance inspections failed to detect the existing corrosion and cracks on the component.
- Inconsistencies in maintenance record-keeping were noted, specifically regarding the lack of documentation for a previous bolt replacement.