On December 24, 2022, about 1653 Pacific standard time, a Beech V35B, N65Y, was substantially damaged when it was involved in an accident near Livermore Municipal Airport (LVK), Livermore, California. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed runway 7L at LVK with the intention of remaining within the airport traffic pattern. While on the upwind leg of the traffic pattern, the cabin door opened, and he slowed the airplane down “using the throttle.” He stated that due to the wind noise, he could not hear the tower controller well and that he could not see the instruments but could see the engine control knobs. The pilot then heard the tower controller say “climb, climb, climb,” and at that time, the pilot realized the airplane was descending toward a building. The pilot stated that he “pushed the throttle in” but the airplane continued to descend and impacted a building. The pilot added that he usually takes off with the mixture full rich, the propeller full forward, and the throttle at full. When he slowed the airplane, he “slowed it with the throttle.” Due to the dark conditions, he could not be sure if he mistakenly pulled the mixture control knob to slow the airplane down. A witness, located near the accident site, reported that they heard the accident airplane’s engine sputtering as it passed by his location, followed by the sound of the airplane impacting a building. Examination of the recovered wreckage revealed no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. Fuel expelled from various fuel lines when they were removed. The engine-driven fuel pump was removed, and the drive shaft was found intact. The fuel pump drive shaft rotated freely by hand. The fuel pump was disassembled and found to be unremarkable. Continuity of the throttle, propeller, and mixture controls was established from the cockpit to their respective control arms and moved from stop to stop by hand. Examination of the engine controls in the cockpit revealed the throttle knob was about 1 inch from full forward, the mixture was about 2 inches from full forward, and the propeller lever was about 1/2 inch from full forward.