What happened
On December 15, 2010, a Beechcraft 95-B55, registration PT-CMT, was performing a cargo transport flight from Fortaleza to Crateús, Ceará. Upon landing at the Crateús Aerodrome (SNWS), the pilot began a left turn to enter the parking apron. During this maneuver, the left main landing gear unexpectedly retracted, causing the aircraft to veer off the runway.
The impact caused the left wingtip, flap, engine, and propeller to strike the ground. The aircraft completed a 45-degree turn before coming to a complete stop near the second runway intersection. The pilot, who was the sole occupant, escaped the aircraft uninjured, and no third-party damage was reported.
The investigation
CENIPA investigators examined the landing gear retraction system, which utilizes a single electric actuator to operate the nose and main gear. The investigation focused on the mechanical integrity of the downlock mechanism and the maintenance history of the aircraft.
Investigators found that the aircraft was within weight and balance limits and that the pilot was properly qualified. While the aircraft had recently undergone a 100-hour inspection, the investigation revealed that a specific component, the uplock roller, was seized. The inspection of the wreckage showed that the left main gear retract rod, support assembly, brace assembly, and the down-lock torsion spring had all failed due to the collapse of the gear system.
Findings
- Inadequate maintenance was a primary factor, as evidenced by corrosion and a lack of proper lubrication on the main gear uplock roller.
- The seized roller prevented the landing gear from properly locking in the down position during the extension process.
- Although the pilot's cockpit indicators showed the gear was down and locked, the mechanical failure of the roller compromised the synchronization required for the gear to remain stable during taxiing.
- The operator's location in a humid, coastal environment necessitated more frequent inspections for corrosion and lubrication, as recommended by the manufacturer's maintenance manual.