What happened
On July 11, 2019, a Beechcraft King Air C90 GTI, registration N989AE, was performing a private flight from Guaymaral to Palonegro International Airport in Lebrija, Colombia. During the approach to runway 35, the pilot encountered contradictory cockpit indications: an audible alarm signaled that the landing gear was in transition, yet three green lights indicated the gear was down and locked. After cycling the gear lever several times without resolving the discrepancy, the pilot requested a visual inspection from the tower, which confirmed the gear appeared to be down.
The aircraft landed normally, but after traveling approximately 6 and 600 meters along the runway, the right main landing gear began to slowly retract. This caused the right wing to make contact with the runway surface, resulting in significant abrasion to the ventral section of the wing. The loss of directional control led the aircraft to exit the runway on the right side, coming to rest in the safety area. All three occupants (the pilot and two passengers) were able to evacuate the aircraft uninjured.
The investigation
The GRIAA investigation focused on the mechanical and electrical integrity of the landing gear system. Investigators examined the aircraft's maintenance history, noting it had only 47.3 flight hours since new and was fully airworthy. The investigation included inspections of the hydraulic system and the landing gear extension/retraction cycle. Technical analysis of the components revealed that the issue was not caused by a hard landing, as no structural damage consistent with such an event was found.
Findings
- The primary cause of the accident was the malfunction of the right landing gear downlock switch. Due to manufacturing and inspection errors, the internal micro-switches within the switch hit their housing, sending erroneous electrical signals to the hydraulic system. This caused the gear to unsecure and retract during the landing roll.
- The pilot experienced a loss of situational awareness because he was attempting to provide flight instruction to another pilot on board who was not part of the scheduled flight. This distraction prevented a more detailed evaluation of the contradictory gear indications and the execution of an emergency manual gear extension.
- The operator lacked a formal risk management system to mitigate operational hazards.
- The aircraft's checklists did not include specific procedures for handling contradictory landing gear indications.