On August 25, 2019, about 1500 central daylight time, a Cessna 425 airplane, N300GD, was substantially damaged when it was involved in an accident near Bethany, Oklahoma. The private pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he planned to fly the airplane locally to test a repaired autopilot. After a normal preflight and engine runup, the pilot initiated the takeoff. After confirming a positive rate of climb, the pilot raised the landing gear and confirmed it was locked in the retracted position. Suddenly, the airplane yawed to the right and left. The pilot determined that directional control was not possible, so he decided to abort the takeoff, reduced the power to idle, and landed gear-up on the remaining runway. The airplane slid off the end of the runway onto a concrete pad, resulting in substantial damage to the left wing. Examination of the airplane’s flight control system at the accident site did not reveal any anomalies. All controls from the cockpit to the flight control surfaces were connected and appeared normal. Further examination of the throttle quadrant and linkages from the quadrant to the engine, including power levers, propeller levers, and fuel condition levers, were conducted at a secure facility. All quadrant levers moved freely and smooth without binding. The friction lock on the right side of the quadrant was found backed off completely with no friction applied. The friction lock was adjusted to apply friction and functioned properly. Both right and left engine power lever connections were connected properly to their respective engines. With the power levers disconnected from the fuel control units (FCUs), the input levers (left and right) on each FCU moved smoothly. All power controls levers and cables were connected and functioned normally.