On April 2, 2005, about 1040 Pacific standard time, a Beech D50C, N50G, struck a hangar and impacted terrain after experiencing a loss of power during takeoff at Montague Airport-Yreka Rohrer Field, Montague, California. The owner/pilot was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, sustained minor injuries; the airplane sustained substantial damage. The local personal flight departed at 1040. Visual meteorological conditions prevailed, and no flight plan had been filed. The approximate global positioning system (GPS) coordinates of the primary wreckage were 41 degrees 43.49 minutes north latitude and 122 degrees 32.44 minutes west longitude. The pilot stated that the airplane and engine had no mechanical failures or malfunctions during the flight. The pilot/owner submitted a Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2). The pilot reported that he had flown the accident airplane from Aurora, California, on March 25, 2005, after an extensive avionics upgrade, which included the installation of a fuel management system. During the flight to Montague, he could smell fuel and noticed that there were streaks on the engine cowling. After landing at Montague he taxied to his hangar, and noticed a puddle of fuel on the ground. He removed the right engine cowling and found a fuel line that was loose and had been leaking. He tightened the fitting, and found no other leaks. He then secured the airplane back in the hangar. On the day of the accident, the pilot conducted a normal preflight. The preflight included looking in the main fuel tanks; the pilot expected the fuel level in each main tank to be about 20 gallons (less than 1/2 tank) based on his amount of flying time. He said that a pilot was not able to visually verify how much fuel was actually present in each tank of this model airplane when the tanks were less than 1/2 full. The pilot stated that he had not considered that the leak during the last flight was enough to have depleted the 20 gallons he thought to be in the right main fuel tank. The engine start, taxing for takeoff, and engine run-ups were normal. The pilot said that the takeoff was normal. After rotation, the airplane veered to the right. He thought that the new autopilot might have engaged. He had the left rudder pedal fully down. He was 40 feet in the air and still going to the right, off the runway, toward his hangar. He applied full left rudder and left aileron. He thought that the airplane was about to stall, so he lowered the nose. The right wing tip impacted a hangar door, and the airplane spun around on its vertical axes. The National Transportation Safety Board investigator in-charge (IIC) had the airplane's fuel system inspected. The fuel system was intact, and had not been breeched during the accident sequence. No fuel was found in the right main tank or in fuel lines for the right engine. The right auxiliary fuel tank was full to its capacity of 46 gallons. The IIC released the wreckage to the owner's representative on April 6, 2005.