What happened
On June 20, 2008, a Cessna 402B, registration PT-OPI, was performing a non-scheduled air transport flight from Teresina, PI, to Fortaleza, CE. The aircraft landed on runway 13 at Fortaleza at approximately 23:32 UTC. During the landing roll, approximately 300 meters after touchdown, the left main landing gear unexpectedly retracted.
This failure caused the aircraft to veer to the left, exiting the runway. During the excursion, the right main landing gear also retracted, and the nose gear sustained damage. The propeller blades of both engines struck the ground while the engines were still operating. The pilot immediately shut down both engines using the fuel selectors to mitigate further damage to the propellers and engines. The aircraft eventually came to a stop approximately 9/0 degrees from the runway centerline, near the general aviation terminal. The pilot and the single passenger were uninjured.
The investigation
CENIPA investigators determined that the left main landing gear retraction was caused by the shear failure of a bolt in the rear part of the left-hand bellcrank assembly. While the aircraft's maintenance records were up to date, investigators could not establish the traceability of the specific bolt involved. Unlike standard NAS-specification bolts, which typically feature embossed markings indicating hardness and tensile strength, the investigated bolt lacked any identifiable technical specifications or part number markings.
Furthermore, the investigation revealed that several threads on the left main landing gear strut terminals were fractured and showed significant signs of corrosion, indicating a poor state of aircraft conservation. Because the operator also functioned as the maintenance provider for the aircraft, the investigation highlighted issues regarding maintenance execution and oversight.
Findings
- Inadequate maintenance of the aircraft.
- Lack of component traceability regarding the bellcrank assembly bolt.
- Presence of corrosion and deteriorated components within the landing gear assembly.
- Inadequate managerial supervision of maintenance processes.