On November 30, 2023, at 1318 eastern standard time, a Raytheon Aircraft Company 400A airplane, N800SD, was substantially damaged when it was involved in an accident at Dekalb-Peachtree Airport (PDK), Atlanta, Georgia. The airline transport pilot and a commercial pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight. According to the pilots, shortly after being cleared for landing on runway 3R at PDK, they configured the airplane for landing and completed the before-landing checklist. They did not observe any abnormalities; the landing gear position indicator showed three green lights and no red handle, which indicated a safe landing gear configuration. The pilots stated that they made a normal landing in the touchdown zone, but during the first part of the landing roll there was a “violent” left yaw and they lost directional control. The airline transport pilot, who was the pilot flying, used full right rudder deflection and aileron to keep the airplane centered on the runway; simultaneously, the landing gear unsafe horn sounded. The commercial pilot then noticed that the landing gear handle was illuminated red, indicating unsafe gear, and the green light for the left main landing gear had extinguished. The airplane was tilted left with the left wing dragging on the runway, then on the grass, before the airplane came to rest about 3,800 ft down the runway. Postaccident examination of the airplane revealed that the left main landing gear was collapsed, and the airplane had sustained substantial damage to the left outboard wing, flaps, and aileron. During recovery of the airplane, airport personnel lowered the left main landing gear and towed the airplane to a hangar. After recovery of the airplane, an operational test of the landing gear system revealed that the left landing gear actuator did not lock the left landing gear. Visual examination of the left landing gear actuator did not reveal any anomalies, and it was not leaking fluid. After the actuator was replaced with another actuator, the landing gear functioned normally. No additional examination of the accident landing gear actuator was performed.