On April 18, 2015, about 1452 central daylight time, a Mooney M20C, N9680M, impacted terrain shortly after takeoff from runway 18 at the Winchester Municipal Airport (BFG), Winchester, Tennessee. The private pilot and two passengers received minor injuries, two passengers received serious injuries. The airplane sustained substantial damage to both wings and fuselage. Visual meteorological conditions prevailed and no flight plan was filed for the local flight. The airplane was privately owned and operated under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. The flight was originating at the time of the accident.The pilot reported that after takeoff, the airplane's engine "lost power" and "put it down in a field across from the end of the runway" to avoid power lines. The pilot also stated that there were five people onboard the airplane. The airplane had four seats, and a baggage area located behind the rear seats. A witness, who worked at the airport, stated that she watched the airplane lift off about halfway down the 5,002-ft-long runway and it did not seem it did not seem to have the proper lift. The airplane seemed to gain altitude then sink as it made a slight left turn at the end of the runway. They airplane then suddenly dropped out of sight. Examination of the wreckage at the scene by a Federal Aviation Administration (FAA) inspector revealed that the airplane impacted a grass field about a 1/4mile south of the runway and came to rest on the edge of a roadway. Both propeller blades exhibited leading edge gouging and chordwise scratches. One blade exhibited aft "s" bending; the other was bent forward about mid span. Recovery personnel drained about 30 gallons of fuel from the airplane at the scene. A postaccident examination of the engine was conducted by an FAA inspector at a secure facility. Engine crankshaft continuity was confirmed on all cylinders, valves, and accessory gears. Continuity of the valvetrain was verified through a thumb compression test. The spark plugs were removed and inspected; each displayed a light gray color. The carburetor bowl was examined and was found to be free of debris. The bowl contained fuel and about 1/2 teaspoon of water. The 1435 recorded weather observation at BGF included wind 170 at 5 knots, visibility 10 miles with few clouds at 8000 feet, temperature 79 degrees F, dew point 57 degrees F; barometric altimeter 29.93 inches of mercury. Review of records revealed that the airplane's basic empty weight was 1,620.8 lbs., with a maximum gross takeoff weight of 2,575 lbs., resulting in a useful load of 954.2 lbs. According to drivers' license records, the five occupants weighed a total of 1,065 lbs., which added to the weight of the fuel (180 lbs.) resulted in a gross weight that was 290.8 lbs. above the airplane's maximum gross weight, not accounting for any baggage. Review of a takeoff performance chart for the airplane revealed that for the given altitude and temperature, the airplane required about 1,700 feet to takeoff and clear a 50-ft obstacle; however, that data assumed the airplane weighed 2,575 lbs.