What happened
On July 3, 2020, a Cessna 414, registration HK-4839, was operating an air ambulance mission from Guaymaral to Santa Marta, Colombia. The flight had previously stopped in Bucaramanga to collect a minor patient and an accompanying adult.
During the approach to Simón Bolívar Airport, the crew noticed that the green indicator light for the left landing gear failed to illuminate after the gear lever was extended. Following the Pilot's Operating Handbook (POH) procedures, the crew cycled the gear, which successfully displayed all three green lights. To ensure safety, the crew requested a low-altitude flyover, and Air Traffic Control confirmed that the gear appeared down and locked.
Despite the visual confirmation, as the aircraft decelerated on the runway, an abnormal noise was heard, and the plane began to veer left. Approximately 562 meters into the landing roll, the left landing gear collapsed completely. The left wing and engine propeller made contact with the asphalt, causing the aircraft to veer sharply toward the left side of the runway. The aircraft came to a stop in the safety area. All six occupants—including the two pilots, medical staff, patient, and companion—evacuated the aircraft without injury, though the aircraft sustained substantial damage.
The investigation
The GRIAA investigation focused on the mechanical failure of the landing gear system. Investigators examined the landing gear assembly and performed Brinell hardness tests on the components. The investigation also reviewed maintenance records, specifically focusing on the removal and installation processes of the landing gear and the adequacy of the operator's maintenance manual regarding component life limits and inspection procedures.
Findings
- The primary cause of the accident was the failure of the left landing gear bellcrank assembly (P/N 5041001-1) due to overload and material aging, which led to the unintended retraction of the gear during the landing roll.
- Material aging of the bellcrank, caused by exposure to various atmospheric and geographic environments, contributed to physical and intergranular wear.
- Potential maintenance errors during the removal and installation of the landing gear, specifically regarding the failure to meticulously verify clearances and backlash.
- A lack of specific procedures in the maintenance manual to limit the service life of such critical components.
- Deficiencies in the manufacturer's inspection processes, which lacked deep non-destructive testing (NDT) requirements for these parts.
- Inadequate inspection procedures within the operator's General Maintenance Manual, which failed to treat landing gear installation as a special task requiring controlled technical oversight.