On January 14, 2006, about 0936 mountain standard time, an unregistered Quicksilver MX II Sprint airplane collided with a tree near Bouse, Arizona, following a loss of engine power. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot was seriously injured; the airplane was substantially damaged. The local personal flight departed Bouse airstrip at an unknown time. Visual meteorological conditions prevailed, and no flight plan had been filed. The approximate global positioning system (GPS) coordinates of the primary wreckage were 33 degrees 56 minutes north latitude and 114 degrees 0 minutes west longitude. An eyewitness stated that the airplane took off and entered a downwind leg at about 200 foot above ground level (agl). Halfway down the downwind leg, the engine quit. The aircraft descended and impacted a tree nose first. A mechanic experienced with ultralight type two-stroke engines (not a licensed Airframe and Powerplant Mechanic) examined the engine from the accident airplane. The mechanic reported that the engine could be rotated by hand, and he measured compression in the left cylinder as 115 psi and 145 psi in the right cylinder. He said that 145 psi would be considered a normal cylinder compression reading. The left cylinder had aluminum stuck to the inside of the cylinder wall on both the intake side and exhaust side. The sparkplug electrodes were light gray or almost white in color, and carbon deposits or buildup was observed on both. The piston domes did not have a good wash pattern and had carbon buildup on the faces. The air filter was barely serviceable. There was oil residue around the exhaust port. The mechanic said that the aluminum deposits inside the left cylinder indicates that the piston seized, probably from overheating, which stopped the engine.